Patent Publication Number: US-9837012-B2

Title: Display device and electronic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Application No. 2015-083657, filed on Apr. 15, 2015, the contents of which are incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a display device and an electronic apparatus. 
     2. Description of the Related Art 
     In recent years, the demand for display devices for mobile apparatuses such as mobile phones and electronic paper has been increased. In the display devices, one pixel includes a plurality of sub-pixels that output light of different colors, and various colors are displayed through one pixel by combining the colors of the sub-pixels. In the display devices, display characteristics such as a resolution and luminance have been improved year after year as well. However, since an aperture ratio decreases as a resolution increases, it is necessary to increase luminance of a backlight in order to implement high luminance, which leads to an increase in power consumption of the backlight. In order to solve this problem, a technique that adds a white sub-pixel serving as a fourth sub-pixel to red, green, and blue sub-pixels serving as first to third sub-pixels known in the art has been proposed. According to this technique, a current value of the backlight is reduced as the white sub-pixel enhances the luminance, and thus the power consumption is reduced. 
     Here, the display device controls light-emitting of a plurality of sub-pixels such that a predetermined color is displayed through one pixel. Thus, the display device commonly performs display driving using a plurality of sub-pixels arranged in one pixel as a set. In other words, the display device commonly performs display driving in units of pixels. Meanwhile, a technique called sub-pixel rendering of performing display driving by controlling outputs of the sub-pixels independently is known. In the sub-pixel rendering, since display driving is independently performed for each sub-pixel, the resolution can be increased in a pseudo manner. The sub-pixel rendering is used, for example, when a font of characters or the like is displayed. 
     Here, when the sub-pixel rendering is performed, for example, the deterioration of the image in which a portion becomes dark is likely to be viewed according to an arrangement direction of the sub-pixels in the pixel. 
     In order to solve the above problems, it is an object of the present invention to provide a display device and an electronic apparatus, which are capable of suppressing the deterioration of the image when the sub-pixel rendering is performed. 
     SUMMARY 
     According to an aspect, a display device includes an image display panel that includes a plurality of pixels that are arranged on a display region of a square shape having a first side and a second side intersecting with the first side in a matrix form and receives image information of a portrait mode in which a direction along the first side is a predetermined one direction of a display image or a landscape mode in which a direction along the second side is the one direction of the display image, each of the plurality of pixels including a first sub-pixel, a second sub-pixel, a third sub-pixel, and a fourth sub-pixel arranged in a 2×2 matrix form, and a signal processing unit that generates output signals from input values of input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel. The signal processing unit includes a rendering position deciding unit that decides whether or not a sub-pixel rendering process is performed, among the plurality of arranged pixels including a first pixel, a second pixel neighboring the first pixel at a side in a predetermined processing direction, and a third pixel neighboring the second pixel at the side in the processing direction, the sub-pixel rendering process changing input signal values of sub-pixels of the second pixel, a pattern information acquiring unit that acquires an arrangement of the sub-pixels in the processing direction of a display mode indicating either of the portrait mode and the landscape mode as pattern information indicating any one of a first arrangement pattern and a second arrangement pattern that differ in the arrangement of the sub-pixels, and a rendering unit that generates rendering input signals of the sub-pixels of the second pixel by performing either of a first sub-pixel rendering process and a second sub-pixel rendering process of the sub-pixel rendering process on input signals of the sub-pixels of the second pixel based on the decision of the rendering position deciding unit and the pattern information, the second sub-pixel rendering process differing from the first sub-pixel rendering process in a change in signal values of the input signals of the sub-pixels. The processing direction is a direction along the first side of the image display panel when the display mode is the portrait mode and a direction along the second side of the image display panel when the display mode is the landscape mode. 
     According to an another aspect, a display device includes an image display panel that includes a plurality of pixels that are arranged on a display region of a square shape having a first side and a second side intersecting with the first side in a matrix form and receives image information of a portrait mode in which a direction along the first side is a predetermined one direction of a display image or a landscape mode in which a direction along the second side is the one direction of the display image, each of the plurality of pixels including a first sub-pixel, a second sub-pixel, a third sub-pixel, and a fourth sub-pixel arranged in a 2×2 matrix form; and a signal processing unit that generates output signals from input values of input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel, wherein the signal processing unit includes a rendering unit that generates a rendering input signal by performing a predetermined sub-pixel rendering process, the plurality of arranged pixels including a first pixel, a second pixel neighboring the first pixel at a side in a predetermined processing direction, and a third pixel neighboring the second pixel at the side in the processing direction, the predetermined sub-pixel rendering process changing signal values of input signals of sub-pixels of the second pixel, a pattern information acquiring unit that acquires an arrangement of the sub-pixels in the processing direction of a display mode indicating either of the portrait mode and the landscape mode as pattern information indicating any one of a first arrangement pattern and a second arrangement pattern that differ in the arrangement of the sub-pixels, a correction process deciding unit that decides whether or not an output signal of the fourth sub-pixel of the second pixel is generated based on the pattern information through a correction process, a fourth sub-pixel generation signal unit that obtains a generation signal of the fourth sub-pixel of the second pixel based on the rendering input signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel, and an expansion coefficient related to the image display panel, based on the decision of the correction process deciding unit, a fourth sub-pixel output signal generating unit that performs the correction process by performing an averaging process based on the generation signal of the fourth sub-pixel of the second pixel and input signals of other sub-pixels, and generates the output signal of the fourth sub-pixel of the second pixel, an output signal generating unit that obtains the output signal of the first sub-pixel of the second pixel based on the rendering input signal of the first sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, obtains the output signal of the second sub-pixel of the second pixel based on the rendering input signal of the second sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and obtains the output signal of the third sub-pixel of the second pixel based on the rendering input signal of the third sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and the processing direction is a direction along the first side of the image display panel when the display mode is the portrait mode and a direction along the second side of the image display panel when the display mode is the landscape mode. 
     According to an another aspect, A display device includes an image display panel that includes a plurality of pixels that are arranged on a display region of a square shape having a first side and a second side intersecting with the first side in a matrix form and receives image information of a portrait mode in which a direction along the first side is a predetermined one direction of a display image or a landscape mode in which a direction along the second side is the one direction of the display image, each of the plurality of pixels including a first sub-pixel, a second sub-pixel, a third sub-pixel, and a fourth sub-pixel arranged in a 2×2 matrix form; and a signal processing unit that generates output signals from input values of input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel, wherein the signal processing unit includes a rendering unit that generates a rendering input signal by performing a predetermined sub-pixel rendering process, the plurality of arranged pixels including a first pixel, a second pixel neighboring the first pixel at a side in a predetermined processing direction, and a third pixel neighboring the second pixel at the side in the processing direction, the predetermined sub-pixel rendering process changing signal values of input signals of sub-pixels of the second pixel, a sub-pixel generation signal unit that generates generation signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel based on the input signal values and the rendering input signal values of the sub-pixels in each of the pixels, a correction process deciding unit that decides whether or not the output signal of the fourth sub-pixel of the second pixel is generated through a correction process based on a generation signal value of a neighboring sub-pixel and generation signal values of both-side sub-pixels, the neighboring subpixel is served as a sub-pixel of the second pixel neighboring the fourth sub-pixel of the second pixel in an orthogonal direction serving as a direction orthogonal to the processing direction, and the both-side sub-pixels are served as a plurality of sub-pixels neighboring the neighboring sub-pixel or the fourth sub-pixel of the second pixel in the processing direction or an opposite direction serving as a direction opposite to the processing direction, a fourth sub-pixel output signal generating unit that performs the correction process based on the decision of the correction process deciding unit, by performing an averaging process based on the generation signal of the fourth sub-pixel of the second pixel and input signals of other sub-pixels, and generates the output signal of the fourth sub-pixel of the second pixel, an output signal generating unit that obtains the output signal of the first sub-pixel of the second pixel based on the rendering input signal of the first sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, obtains the output signal of the second sub-pixel of the second pixel based on the rendering input signal of the second sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and obtains the output signal of the third sub-pixel of the second pixel based on the rendering input signal of the third sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and the processing direction is a direction along the first side of the image display panel when the image information corresponds to the portrait mode and a direction along the second side of the image display panel when the image information corresponds to the landscape mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an exemplary configuration of a display device according to a first embodiment; 
         FIG. 2  is a conceptual diagram of an image display panel according to the first embodiment; 
         FIG. 3  is a schematic diagram illustrating a sub-pixel arrangement according to the first embodiment; 
         FIG. 4A  is a schematic diagram for describing a portrait mode and a landscape mode; 
         FIG. 4B  is a schematic diagram for describing a portrait mode and a landscape mode; 
         FIG. 5  is a schematic diagram illustrating an example of a sub-pixel arrangement in a portrait mode; 
         FIG. 6  is a schematic diagram illustrating an example of a sub-pixel arrangement in a landscape mode; 
         FIG. 7  is a block diagram illustrating an overview of a configuration of a signal processing unit according to the first embodiment; 
         FIG. 8  is a schematic diagram illustrating an example of a display when a certain rendering process is not performed; 
         FIG. 9  is a schematic diagram illustrating an example of a display when a certain rendering process is performed; 
         FIG. 10  is a schematic diagram for describing an input signal when a rendering process is performed; 
         FIG. 11  is a schematic diagram illustrating an example of a sub-pixel arrangement in a first arrangement pattern; 
         FIG. 12  is a schematic diagram illustrating an example of a sub-pixel arrangement a second arrangement pattern; 
         FIG. 13  is a schematic diagram for describing a rendering input signal generated by an RGB rendering process; 
         FIG. 14  is a schematic diagram for describing a rendering input signal generated by a BGR rendering process; 
         FIG. 15  is a conceptual diagram of an extended HSV color space that is extendable by the display device according to the first embodiment; 
         FIG. 16  is a conceptual diagram illustrating a relation between a hue and a saturation of an extended HSV color space; 
         FIG. 17  is a flowchart for describing a process operation a signal processing unit according to the first embodiment; 
         FIG. 18  is a schematic diagram illustrating output signals of sub-pixels when a rendering process according to a first comparative example is performed; 
         FIG. 19  is a schematic diagram illustrating output signals of sub-pixels when the rendering process according to the first embodiment is performed; 
         FIG. 20A  is a table indicating a relation among a display mode, an arrangement pattern, and a rendering process of the image display panel according to the first embodiment; 
         FIG. 20B  is a table indicating a relation among a display mode, an arrangement pattern, and a rendering process of another example of an image display panel according to the first embodiment; 
         FIG. 21  is a block diagram illustrating a configuration of a signal processing unit according to a second embodiment; 
         FIG. 22A  is a flowchart for describing process operations of a rendering processing unit and a correction process deciding unit according to the second embodiment; 
         FIG. 22B  is a flowchart for describing process operations of a rendering processing unit and a correction process deciding unit according to another example of the second embodiment; 
         FIG. 23A  is a schematic diagram illustrating an example of output signals of sub-pixels when a rendering process and a correction process according to the second embodiment are performed; 
         FIG. 23B  is a schematic diagram illustrating another example of output signals of sub-pixels when the rendering process and the correction process according to the second embodiment are performed; 
         FIG. 24A  is a table indicating a relation between a display mode and a condition of a pixel that undergoes a correction process in the image display panel according to the second embodiment; 
         FIG. 24B  is a table indicating a relation between a display mode and a condition of a pixel that undergoes a correction process in another example of the image display panel according to the second embodiment; 
         FIG. 25  is a block diagram illustrating a configuration of a signal processing unit according to a third embodiment; 
         FIG. 26  is a schematic diagram illustrating an arrangement of sub-pixels and generation signal values thereof; 
         FIG. 27  is a flowchart for describing a process operation of the signal processing unit according to the third embodiment; 
         FIG. 28  is a schematic diagram illustrating output signals of sub-pixels when a rendering process and a correction process according to the third embodiment are performed; 
         FIG. 29  is a schematic diagram illustrating an example of a sub-pixel arrangement in a portrait mode according to a modification; 
         FIG. 30  is a schematic diagram illustrating an example of a sub-pixel arrangement in a landscape mode according to a modification; 
         FIG. 31  is a schematic diagram illustrating output signals of sub-pixels when a rendering process according to a second comparative example is performed; 
         FIG. 32  is a schematic diagram illustrating output signals of sub-pixels when a rendering process according to a modification is performed; 
         FIG. 33  is a schematic diagram illustrating output signals of sub-pixels when a rendering process according to a third comparative example is performed; 
         FIG. 34  is a schematic diagram illustrating output signals of sub-pixels when a rendering process according to a modification is performed; and 
         FIG. 35  is a diagram illustrating an example of an electronic apparatus to which the display device according to the first embodiment is applied. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. The disclosure is given by way of example, and modifications that maintain the gist of the present invention and are easily conceivable by those skilled in the art are included in the present invention. To further clarify the description, the width, thickness, shape, and the like of each component may be schematically illustrated in the drawings as compared to actual aspects, and they are given by way of example and interpretation of the present invention is not limited to them. The same elements as those described in the description with reference to some drawings are denoted by the same reference numerals through the description and the drawings, and detailed descriptions thereof will be omitted in some cases. 
     First Embodiment 
     Overall Configuration of Display Device 
     First, a first embodiment (a first aspect) will be described.  FIG. 1  is a block diagram of an exemplary configuration of a display device according to a first embodiment. A display device  10  according to the first embodiment includes a signal processing unit  20 , an image display panel driving unit  30 , an image display panel  40 , a light source driving unit  50 , and a light source unit  60  as illustrated in  FIG. 1 . The signal processing unit  20  receives an input signal (RGB data) from an image output unit  12  of a control device  11 , and transfers a signal generated by performing a predetermined data conversion process on the input signal to the respective units of the display device  10 . The image display panel driving unit  30  controls driving of the image display panel  40  based on the signal received from the signal processing unit  20 . The light source driving unit  50  controls driving of the light source unit  60  based on the signal received from the signal processing unit  20 . The light source unit  60  illuminates the back surface of the image display panel  40  with light based on the signal received from the light source driving unit  50 . The image display panel  40  displays an image based on the signal received from the image display panel driving unit  30  and the light emitted from the light source unit  60 . The control device  11  includes a display mode deciding unit  13  that detects a direction in the vertical direction of the display device  10  through an acceleration sensor, and decides a display mode of the image display panel  40 . 
     Configuration of Image Display Panel 
     First, a configuration of the image display panel  40  will be described.  FIG. 2  is a conceptual diagram the image display panel according to the first embodiment.  FIG. 3  is a schematic diagram illustrating a sub-pixel arrangement according to the first embodiment. The image display panel  40  includes a display region  43  in which P 0 ×Q 0  pixels  48  (P 0  pixels in an X direction and Q 0  pixels in a Y direction) are arranged in a two-dimensional (2D) matrix form as illustrated in  FIGS. 1, 2, and 3 . Here, the X direction is the row direction of an image displayed on the image display panel  40 . The Y direction is a direction orthogonal to the X direction, that is, the column direction of an image displayed on the image display panel  40 . An embodiment is not limited thereto, and the X direction may be the column direction of the image, and the Y direction may be the row direction of the image. The display region  43  of the image display panel  40  has a rectangular shape including a short side  41  serving as a first side and a long side  42  serving as a second side intersecting with the short side  41  as illustrated in  FIG. 1 . The display region  43  may have a quadrangular shape, for example, a square shape in which the short side  41  and the long side  42  have the same length. 
     Each of the pixels  48  includes a first sub-pixel  49 R, a second sub-pixel  49 G, a third sub-pixel  49 B, and a fourth sub-pixel  49 W as illustrated in  FIGS. 2 and 3 . The first sub-pixel  49 R displays a first color (red in the first embodiment). The second sub-pixel  49 G displays a second color (green in the first embodiment). The third sub-pixel  49 B displays a third color (blue in the first embodiment). The fourth sub-pixel  49 W displays a fourth color (white in the first embodiment). The first, the second, the third, and the fourth colors are not limited to red, green, blue, and white, respectively, and simply need only to be different from one another, such as complementary colors. The fourth sub-pixel  49 W that displays the fourth color preferably has higher luminance than that of the first sub-pixel  49 R that displays the first color, the second sub-pixel  49 G that displays the second color, and the third sub-pixel  49 B that displays the third color when they are irradiated with light with the same light source lighting amount. In the following description, when it is unnecessary to distinguish the first sub-pixel  49 R, the second sub-pixel  49 G, the third sub-pixel  49 B, and the fourth sub-pixel  49 W, they are referred to as a “sub-pixel  49 .” To distinguish and specify a position at which a sub-pixel is arranged, for example, a fourth sub-pixel in a pixel  48   (p,q)  is referred to as a “fourth sub-pixel  49 W (p,q) .” 
     As illustrated in  FIG. 3 , the pixel  48  includes the four sub-pixels  49  which are arranged in a 2×2 matrix form. The four sub-pixels  49  are 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. 
     The image display panel  40  receives image information corresponding to a portrait mode or a landscape mode according to decision of the display mode deciding unit  13  of the control device  11 . Here, the image information is information for displaying an image. In further detail, the control device  11  outputs an input signal corresponding to the display mode of either of the portrait mode and the landscape mode to the signal processing unit  20  according to the decision of the display mode deciding unit  13 . Then, the signal processing unit  20  generates an output signal based on the input signal. The image display panel driving unit  30  generates image information (video signal) for displaying an image based on the output signal, and outputs the image information to the image display panel  40 .  FIGS. 4A and 4B  are schematic diagrams for describing the portrait mode and the landscape mode.  FIGS. 4A and 4B  illustrate examples in which an alphabet A is displayed on the image display panel  40 . 
     Here, as illustrated in  FIG. 4A , in the portrait mode, the short side  41  of the image display panel  40  lies in the X direction serving as the row direction of the image. In the portrait mode, the long side  42  of the image display panel  40  lies in the Y direction serving as the column direction of the image. On the other hand, as illustrated in  FIG. 4B , in the landscape mode, the short side  41  lies in the Y direction serving as the column direction of the image. In the landscape mode, the long side  42  lies in the X direction serving as the row direction of the image. In other words, the image display panel  40  sets a direction along the short side  41  as a predetermined one direction (here, the X direction) of a display image in the portrait mode, and sets a direction along the long side  42  as the predetermined one direction (here, the X direction) of a display image in the landscape mode. 
     The portrait mode and the landscape mode are not limited to the examples illustrated in  FIGS. 4A and 4B . Here, in the direction along the X direction, one direction is referred to as a “first direction F 1 ,”, the other direction is referred to as a “second direction F 2 .” Further, in the direction along the Y direction, one direction is referred to as a “third direction F 3 ,” and the other direction is referred to as a “fourth direction F 4 .” The portrait mode includes a first portrait mode (see  FIG. 4A ) in which the short side  41  is positioned at a side of the image in the third direction F 3  and a second portrait mode in which the short side  41  is positioned at a side of the image in the fourth direction F 4 . The landscape mode includes a first landscape mode (see  FIG. 4B ) in which the short side  41  is positioned at a side of the image in the first direction F 1  and a second landscape mode in which the short side  41  is positioned at a side of the image in the second direction F 2 . The image display panel  40  is preferably capable of displaying at least one portrait mode and at least one landscape mode. The first direction F 1 , the second direction F 2 , the third direction F 3 , and the fourth direction F 4  are not limited to the above directions as long as the first direction F 1 , the second direction F 2 , the third direction F 3 , and the fourth direction F 4  are one directions along the X direction or the Y direction and different. 
     Here, arrangement orders of the pixels  48  and the sub-pixels  49  are fixed to the short side  41  and the long side  42  of the image display panel  40 . Thus, as will be described later, the arrangement orders of the pixels  48  and the sub-pixels  49  in the X direction and the Y direction change according to the display mode. 
       FIG. 5  is a schematic diagram illustrating an example of a sub-pixel arrangement in the portrait mode.  FIG. 6  is a schematic diagram illustrating an example of a sub-pixel arrangement in the landscape mode.  FIG. 5  illustrates the first portrait mode in which the short side  41  is positioned at the side of the image in the third direction F 3 . In the portrait mode illustrated in  FIG. 5 , a pixel  48   (1,1)  and a pixel  48   (2,1)  are arranged in the first direction F 1  in this order. Further, in the portrait mode illustrated in  FIG. 5 , the pixel  48   (1,1)  and a pixel  48   (1,2)  are arranged in the third direction F 3  in this order. 
     In the landscape mode illustrated in  FIG. 6 , the pixel  48   (1,1)  and the pixel  48   (2, 1)  are arranged in the third direction F 3  in this order. Further, in the landscape mode illustrated in  FIG. 6 , the pixel  48   (1,1)  and the pixel  48   (1,2)  are arranged in the second direction F 2  in this order. As described above, the arrangement order of the pixels  48  in the X direction and the Y direction changes according to the display mode. 
     As described above, when the X direction is the row direction of the image, and the Y direction is the column direction of the image, in the portrait mode illustrated in  FIG. 5 , the second sub-pixel  49 G is arranged in the first row of the first column of the pixel  48 . The third sub-pixel  49 B is arranged in the second row of the first column of the pixel  48 . The first sub-pixel  49 R is arranged in the first row of the second column of the pixel  48 . The fourth sub-pixel  49 W is arranged in the second row of the second column of the pixel  48 . In other words, in the portrait mode illustrated in  FIG. 5 , the second sub-pixel  49 G and the first sub-pixel  49 R are arranged in the first direction F 1  in this order. Further, in the portrait mode illustrated in  FIG. 5 , the third sub-pixel  49 B and the fourth sub-pixel  49 W are arranged in the first direction F 1  in this order. Further, in the portrait mode illustrated in  FIG. 5 , the second sub-pixel  49 G and the third sub-pixel  49 B are arranged in the third direction F 3  in this order, and the first sub-pixel  49 R and the fourth sub-pixel  49 W are arranged in the third direction F 3  in this order. 
     In the sub-pixel arrangement of the landscape mode in  FIG. 6 , the first sub-pixel  49 R is arranged in the first row of the first column of the pixel  48 , the second sub-pixel  49 G is arranged in the second row of the first column of the pixel  48 , the fourth sub-pixel  49 W is arranged in the first row of the second column of the pixel  48 , and the third sub-pixel  49 B is arranged in the second row of the second column of the pixel  48 . In other words, in the landscape mode illustrated in  FIG. 6 , the first sub-pixel  49 R and the fourth sub-pixel  49 W are arranged in the first direction F 1  in this order, and the second sub-pixel  49 G and the third sub-pixel  49 B are arranged in the first direction F 1  in this order. Further, in the landscape mode illustrated in  FIG. 6 , the first sub-pixel  49 R and the second sub-pixel  49 G are arranged in the third direction F 3  in this order, and the fourth sub-pixel  49 W and the third sub-pixel  49 B are arranged in the third direction F 3  in this order. As described above, the sub-pixel arrangement in the X direction and the Y direction changes according to the display mode. The arrangement is not limited to the examples illustrated in  FIGS. 5 and 6  as long as the sub-pixels  49  are arranged in the pixel  48  in the 2×2 matrix form. Hereinafter, unless otherwise set forth, the arrangements of the pixels  48  and the sub-pixels  49  are assumed to be the arrangements in the first portrait mode illustrated in  FIG. 5 . 
     Configuration of Image Display Panel Driving Unit 
     The image display panel driving unit  30  includes a signal output circuit  31  and a scanning circuit  32  as illustrated in  FIGS. 1 and 2 . The image display panel driving unit  30  holds video signals (the image information) in the signal output circuit  31  and sequentially outputs the video signals to the image display panel  40 . More specifically, the signal output circuit  31  outputs an image output signal having a certain electric potential corresponding to the output signal from the signal processing unit  20  to the image display panel  40 . The signal output circuit  31  is electrically connected to the image display panel  40  through signal lines DTL. The scanning circuit  32  controls an ON/OFF operation of a switching element (e.g., a thin-film transistor (TFT)) that controls an operation (light transmittance) of the sub-pixel  49  in the image display panel  40 . The scanning circuit  32  is electrically connected to the image display panel  40  through wirings SCL. 
     Configurations of Light Source Driving Unit and Light Source Unit 
     The light source driving unit  50  controls the amount of light output from the light source unit  60 , for example. Specifically, the light source driving unit  50  adjusts, for example, a voltage supplied to the light source unit  60  through pulse width modulation (PWM) based on a light source driving signal SBL output from the signal processing unit  20 , and a light amount (intensity of light) of light with which the image display panel  40  is irradiated. 
     The light source unit  60  is arranged on the back surface of the image display panel  40 , and emits light toward the image display panel  40  and illuminates the image display panel  40  with light. The light source unit  60  irradiates the image display panel  40  with light, and makes the image display panel  40  brighter. 
     Configuration of Signal Processing Unit 
     The signal processing unit  20  processes an input signal received from the control device  11 , and generates an output signal. The signal processing unit  20  converts an input value of the input signal displayed by combining red (the first color), green (the second color), and blue (the third color) into an extended value (output signal) in an extended color space (a HSV (Hue-Saturation-Value, Value is also called Brightness) color space in the first embodiment) extended by red (the first color), green (the second color), blue (the third color), and white (the fourth color), and generates the output value. The signal processing unit  20  outputs the generated output signal to the image display panel driving unit  30 . The extended color space will be described later. While the extended color space according to the first embodiment is the HSV color space, it is not limited thereto, and any other coordinate system such as an XYZ color space and a YUV space may be the expanded color space. The signal processing unit  20  also generates the light source driving signal SBL to be output to the light source driving unit  50 . 
       FIG. 7  is a block diagram illustrating an overview of a configuration of the signal processing unit according to the first embodiment. The signal processing unit  20  includes a rendering position deciding unit  21 , a pattern information acquiring unit  22 , a rendering unit  24 , and an output processing unit  26  as illustrated in  FIG. 7 . The respective units of the signal processing unit  20  may be independent units (circuits or the like) or may be a common unit. 
     The rendering position deciding unit  21  acquires an input signal for causing each pixel to display a predetermined color from the control device  11 . The rendering position deciding unit  21  decides the pixel  48  to which a sub-pixel rendering process is performed based on the input signal of each pixel. The rendering position deciding unit  21  outputs rendering position information serving as information of the pixel  48  that is decided to undergo the sub-pixel rendering process and the input signal of each pixel to the rendering unit  24 . The sub-pixel rendering process is a process of performing display driving in units of sub-pixels and changing an input signal of each sub-pixel  49  belonging to the same pixel  48 . A method of deciding the pixel  48  to which the sub-pixel rendering process is performed will be described later. Hereinafter, the sub-pixel rendering process is referred to appropriately as a rendering process. 
     The pattern information acquiring unit  22  acquires pattern information from the display mode deciding unit  13  of the control device  11 . The pattern information is information indicating whether the arrangement order of the sub-pixels  49  in the display mode of the image display panel  40  is a first arrangement pattern or a second arrangement pattern. The first arrangement pattern corresponds to two of the first portrait mode, the second portrait mode, the first landscape mode, and the second landscape mode, and the second arrangement pattern corresponds to the other two. The first arrangement pattern and the second arrangement pattern will be described later in detail. 
     The rendering unit  24  includes a rendering selecting unit  72  and a rendering processing unit  74 . The rendering selecting unit  72  acquires the pattern information from the pattern information acquiring unit  22 . The rendering selecting unit  72  selects one of an RGB rendering process (a first sub-pixel rendering process) and a BGR rendering process (a second sub-pixel rendering process) which is to be performed based on the pattern information. The rendering selecting unit  72  outputs rendering information serving as information of the selected rendering process to the rendering processing unit  74 . The RGB rendering process and the BGR rendering process will be described later. 
     The rendering processing unit  74  acquires the rendering position information and the input signal from the rendering position deciding unit  21 . The rendering processing unit  74  acquires the rendering information from the rendering selecting unit  72 . The rendering processing unit  74  performs the selected rendering process on the input signal of a predetermined pixel  48  based on the input signal of each pixel  48 , the rendering position information, and the rendering information. The rendering processing unit  74  performs the rendering process on the input signal of the pixel  48  that is decided to undergo the rendering process, so as to generate a rendering input signal of the pixel  48 . 
     The output processing unit  26  includes an α calculating unit  82  and an output signal generating unit  88 . The α calculating unit  82  acquires the rendering input signal of the pixel  48  that has undergone the rendering process and the input signal of another pixel  48  from the rendering processing unit  74 . The α calculating unit  82  calculates an expansion coefficient α related to the image display panel  40  based on the rendering input signal and the input signal. The expansion coefficient α is used for expanding the rendering input signal value and the input signal value. A process of calculating the expansion coefficient α will be described later. 
     The output signal generating unit  88  acquires the expansion coefficient α, the rendering input signal of the pixel  48  that has undergone the rendering process, and the input signal of another pixel  48  from the α calculating unit  82 . The output signal generating unit  88  generates the output signals of the sub-pixels  49  in the pixels  48  based on the expansion coefficient α, the rendering input signal of a predetermined pixel  48 , and the input signal of another pixel  48 . The output signal generating unit  88  outputs the generated output signals to the image display panel driving unit  30 . An output signal generation process will be described later. 
     Overview of Rendering Process 
     Next, an overview of the rendering process will be described. The display device commonly performs display driving with a plurality of sub-pixels arranged in one pixel as a set. In other words, the display device commonly performs display driving in units of pixels. Meanwhile, the rendering process is a process of performing display driving in units of sub-pixels by controlling outputs of the sub-pixels independently. An example of a display when a predetermined rendering process serving as an example of the rendering process is performed will be described below.  FIG. 8  is a schematic diagram illustrating an example of a display when a certain rendering process is not performed.  FIG. 9  is a schematic diagram illustrating an example of a display when a certain rendering process is performed. As illustrated in  FIGS. 8 and 9 , in this description, an image display panel  40 X differs from the image display panel  40  according to the first embodiment in a sub-pixel arrangement. In the image display panel  40 X, each of pixels  48 X includes a first sub-pixel  49 XR, a second sub-pixel  49 XG, and a third sub-pixel  49 XB which are arranged in the X direction in a stripe form. 
       FIG. 8  illustrates an example in which regions of two different colors obtained by dividing a rectangle by a diagonal line are displayed. Black is assumed to be displayed on a region on the left of  FIG. 8 , and white is assumed to be displayed on a region on the right of  FIG. 8 . In  FIG. 8 , since the rendering process is not performed, a display of sub-pixels  49 X belonging to one pixel  48 X is decided based on a color displayed by the corresponding pixel. For example, a pixel  48 X 1  illustrated in  FIG. 8  is positioned on the diagonal line between the two regions. When the rendering process is not performed, the pixel  48 X 1  displays white. All the sub-pixels  49 X of the pixel  48 X 1  emit light at the maximum level so that the pixel  48 X 1  displays white. For example, pixel  48 X 2  illustrated in  FIG. 8  is positioned on the diagonal line between the two regions, and displays black. All the sub-pixels  49 X of the pixel  48 X 2  do not emit light so that the pixel  48 X 2  displays black. 
       FIG. 9  illustrates an example in which the same display as in  FIG. 8  is performed through the image display panel  40 X. In  FIG. 9 , since a certain rendering process is performed, display driving is performed for each sub-pixel  49 X. When the certain rendering process is performed, the first sub-pixel  49 XR of the pixel  48 X 1  does not emit light, unlike the example of  FIG. 8 . Further, when the certain rendering process is performed, the third sub-pixel  49 XR of the pixel  48 X 2  emits light, unlike the example of  FIG. 8 . Through the predetermined rendering process, the diagonal line between the two regions illustrated in  FIG. 9  is displayed to be smoother than the diagonal line illustrated in  FIG. 8 . As described above, when the rendering process such as the certain rendering process is performed, the resolution can be improved in the pseudo manner, and thus, for example, a display of a line can be smoother. 
     Process Operation of Signal Processing Unit 
     Process of Deciding Pixel that Undergoes Rendering Process 
     Next, a process operation of the signal processing unit  20  will be described. First, a process of deciding the pixel  48  that undergoes the rendering process will be described. The rendering position deciding unit  21  receives the input signal of each pixel from the control device  11 . Specifically, for a (p, q)-th pixel  48   (p,q)  (here, 1≦p≦P 0  and 1≦q≦Q 0 ), a signal including an input signal of a first sub-pixel  49 R (p,q)  having a signal value of x 1−(p,q) , an input signal of a second sub-pixel  49 G (p,q)  having a signal value of x 2−(p,q) ), and an input signal of a third sub-pixel  49 B (p,q)  having a signal value of x 3−(p,q)  is input to the rendering position deciding unit  21 . The input signal of the first sub-pixel  49 R (p,q)  is the input signal for causing the first sub-pixel  49 R (p,q)  displaying the first color to display the color, and is not actually input to the first sub-pixel  49 R (p,q) . In other words, the input signal of the first sub-pixel  49 R (p,q)  is a signal for causing the first sub-pixel  49 R (p,q)  to display the first color. The same applies to the input signal of the second sub-pixel  49 G (p,q)  and the input signal of the third sub-pixel  49 B (p,q) . 
     The rendering process according to the first embodiment is a process of gradually changing the input signal values of the sub-pixels for some of a plurality of pixels  48  that are adjacent to one another in a processing direction in which the rendering process is performed. In the first embodiment, the processing direction is the first direction F 1 . However, the processing direction may be any one of the second direction F 2 , the third direction F 3 , and the fourth direction F 4 . The rendering process according to the first embodiment is a process of changing the input signal values of the sub-pixels of the pixel  48  that undergoes the rendering process. 
     The rendering position deciding unit  21  decides the pixel  48  that undergoes the rendering process based on the input signals of the pixels. The rendering processing unit  74  performs the rendering process when a difference between the input signal values of the sub-pixels of a pixel neighboring a certain pixel  48  in the first direction F 1  serving as the processing direction and the input signal values of the sub-pixels of a pixel neighboring the pixel  48  in the second direction F 2  serving as a direction opposite to the processing direction is a predetermined value or more. Here, a (a, b)-th pixel  48   (a,b)  (a first pixel), a pixel  48   (a+1,b)  (a second pixel) neighboring the pixel  48   (a,b)  in the processing direction (here, the first direction F 1 ), and a pixel  48   (a+2,b)  (a third pixel) neighboring the pixel  48   (a+1,b)  in the processing direction (here, the first direction F 1 ) are considered. The rendering processing unit  74  decides to perform the rendering process on the pixel  48   (a+1,b)  when a difference between the input signal values of the sub-pixels  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more. The rendering processing unit  74  decides not to perform the rendering process on the pixel  48   (a+1,b)  when a difference between the input signal values of the sub-pixels  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is smaller than the predetermined threshold value. Here, the predetermined threshold value can be arbitrarily set. 
     More specifically, the rendering position deciding unit  21  decides to perform the rendering process on the pixel  48   (a+1,b)  when the input signal value x 1−(a,b)  of the first sub-pixel of the pixel  48   (a,b) , the input signal value x 2−(a,b)  of the second sub-pixel thereof, the input signal value x 3−(a,b)  of the third sub-pixel thereof are the same value, the input signal value x 1−(a+2,b)  of the first sub-pixel of the pixel  48   (a+2,b) , the input signal value x 2−(a+2,b)  of the second sub-pixel thereof, and the input signal value x 3−(a+2,b)  of the third sub-pixel thereof are the same values, and a difference between the input signal values of the sub-pixels  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more. The input signal values of the sub-pixels of the pixel  48   (a,b)  may not be the same in a condition for deciding whether or not the rendering process is performed. For example, the rendering processing unit  74  may decide to perform the rendering process when a difference between an average value of the input signal values of the sub-pixels of the pixel  48   (a,b)  and an average value of the input signal values of the sub-pixels of the pixel  48   (a+2,b)  is a predetermined value or more. 
       FIG. 10  is a schematic diagram for describing an input signal when the rendering process is performed.  FIG. 10  illustrates input signal values of sub-pixels of a pixel  48   (a,b) , a pixel  48   (a+1,b) , a pixel  48   (a+2,b) , a pixel  48   (a+3,b) , and a pixel  48   (a+4,b)  arranged in the X direction. For example, R and 255 written in the pixel  48   (a,b)  of  FIG. 10  indicate that the input signal value x 1−(a,b)  of the first sub-pixel  49 R (a,b)  is 255. Similarly, G and 255 written in the pixel  48   (a,b)  of  FIG. 10  indicate that the input signal value x 2−(a,b)  of the second sub-pixel  49 G (a,b)  is 255. Similarly, B and 255 written in the pixel  48   (a,b)  of  FIG. 10  indicate that the input signal value x 3−(a,b)  of the third sub-pixel  49 B (a,b)  is 255. In the first embodiment, the input signal value has an integer value of 0 to 255. A direction from the pixel  48   (a,b)  to the pixel  48   (a+1,b)  is the first direction F 1 . A direction from the pixel  48   (a+1,b)  to the pixel  48   (a,b)  is the second direction F 2 . 
     As illustrated in  FIG. 10 , the input signal values of the sub-pixels  49   (a,b)  in the pixel  48   (a,b)  are 255. The input signal values of the sub-pixels  49   (a+1,b)  in the pixel  48   (a+1,b)  are 255. The input signal values of the sub-pixels  49   (a+2,b)  in the pixel  48   (a+2,b)  are 100. The input signal values of the sub-pixels  49   (a+3,b)  in the pixel  48   (a+3,b)  are 255. The input signal values of the sub-pixels  49   (a+4,b)  in the pixel  48   (a+4,b)  are 255. The input signal values of the sub-pixels  49   (a+4,b)  in the pixel  48   (a+4,b)  are 255. In this case, the pixel  48   (a+2,b)  displays gray, and the other pixels display white. 
     Here, for example, a predetermined threshold value is assumed to be 100. A difference between the input signal values of the sub-pixels of the pixel  48   (a,b)  and the input signal values of the sub-pixels of the pixel  48   (a+2,b ) is 155, and larger than the predetermined threshold value. Thus, the rendering position deciding unit  21  decides to perform the rendering process on the pixel  48   (a+1,b) . Similarly, a difference between the input signal values of the sub-pixels of the pixel  48   (a+2,b)  and the input signal values of the sub-pixels of the pixel  48   (a+4,b)  is 155 and larger than the predetermined threshold value. Thus, the rendering position deciding unit  21  decides to perform the rendering process on the pixel  48   (a+3,b) . 
     As described above, in the portrait mode, the short side  41  of the image display panel  40  lies in the X direction (the first direction F 1 ). In the landscape mode, the long side  42  of the image display panel  40  lies in the X direction (the first direction F 1 ). Thus, the processing direction is a direction along the short side  41  of the image display panel  40  in the portrait mode and a direction along the long side  42  of the image display panel  40  in the landscape mode. The processing direction is used for selection of the pixel  48  that undergoes the rendering process. Thus, there are cases in which the pixel  48  selected for the rendering process by the rendering position deciding unit  21  changes according to the display mode. 
     Process of Acquiring Pattern Information 
     Next, a process of acquiring the pattern information through the pattern information acquiring unit  22  will be described. The display mode deciding unit  13  of the control device  11  detects the direction of the display device  10  in the vertical direction, for example, using an acceleration sensor. The display mode deciding unit  13  decides the display mode indicating any one of the first portrait mode, the second portrait mode, the first landscape mode, and the second landscape mode to which the image display panel  40  is set based on the direction of the display device  10 . The control device  11  outputs the input signal corresponding to the display mode to the signal processing unit  20 . The display mode deciding unit  13  determines whether the decided display mode is the first arrangement pattern or the second arrangement pattern, and generates pattern information indicating the first arrangement pattern or the second arrangement pattern. The pattern information acquiring unit  22  acquires the pattern information. The display mode deciding unit  13  may decide the display mode based on, for example, an input of an operator or activation of an application in addition to the direction of the display device  10 . 
     The display mode deciding unit  13  may output only the information of the display mode (the first portrait mode, the second portrait mode, the first landscape mode, or the second landscape mode) to the pattern information acquiring unit  22 , and the pattern information acquiring unit  22  may determine whether the display mode is the first arrangement pattern or the second arrangement pattern. The display mode deciding unit  13  may include the display device  10 . 
     Next, the first arrangement pattern and the second arrangement pattern will be described. The image display panel  40  changes a positional relation between the first direction F 1  serving as the row direction of the display image and the short side  41  and the long side  42  by switching the display mode. As described above, the arrangement order of the sub-pixels  49  in the first direction F 1  changes according to the display mode. Since the processing direction in which the rendering process is performed corresponds to the first direction F 1 , the arrangement order of the sub-pixels  49  in the processing direction can be described as changing according to the display mode. The first arrangement pattern and the second arrangement pattern differ from each other in the arrangement order of the sub-pixels  49  in the processing direction. Specifically, an arrangement of the sub-pixels  49  in the first arrangement pattern is an arrangement in which the second sub-pixel  49 G belonging to the same pixel  48  is adjacent to the side of the first sub-pixel  49 R in the processing direction (here, the first direction F 1 ) or an arrangement in which the third sub-pixel  49 B belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (here, the first direction F 1 ). The arrangement of the sub-pixels  49  in the second arrangement pattern is an arrangement in which the first sub-pixel  49 R belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (here, the first direction F 1 ) or an arrangement in which the second sub-pixels  49 G belonging to the same pixel  48  is adjacent to the side of the third sub-pixel  49 B in the processing direction (here, the first direction F 1 ). 
       FIG. 11  is a schematic diagram illustrating an example of a sub-pixel arrangement in the first arrangement pattern.  FIG. 12  is a schematic diagram illustrating an example of a sub-pixel arrangement in the second arrangement pattern. In the example of the sub-pixel arrangement of the first arrangement pattern illustrated in  FIG. 11 , the third sub-pixel  49 B belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (the first direction F 1 ). In the sub-pixel arrangement of the second arrangement pattern illustrated in  FIG. 12 , the first sub-pixel  49 R belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (the first direction F 1 ). The example of  FIG. 11  corresponds to the first landscape mode of  FIG. 6 , and the example of  FIG. 12  corresponds to the first portrait mode of  FIG. 5 . 
     In the first embodiment, when the display mode of the image display panel  40  is the first landscape mode or the second portrait mode, the display mode deciding unit  13  determines that the sub-pixel arrangement has the first arrangement pattern. Further, when the display mode of the image display panel  40  is the first portrait mode or the second landscape mode, the display mode deciding unit  13  determines that the sub-pixel arrangement has the second arrangement pattern. In the image display panel  40 , when the display mode (the first portrait mode, the second portrait mode, the first landscape mode, or the second landscape mode) is fixed, the arrangement of the sub-pixels  49  is decided at the time of design. The display mode deciding unit  13  stores a relation between the display mode and the first and second arrangement patterns. The relation between the display mode and the first and second arrangement patterns differs according to a design of the sub-pixel arrangement and is not limited to the relation in the first embodiment. 
     Selection and Execution of Rendering Process 
     Next, selection and execution of the rendering process by the rendering unit will be described. The rendering selecting unit  72  selects any one of the RGB rendering process (the first sub-pixel rendering process) and the BGR rendering process (the second sub-pixel rendering process) based on the pattern information. As will be described later in detail, the rendering processing unit  74  performs the selected rendering process on the input signal of the pixel  48  decided to undergo the rendering process, and generates the rendering input signal of the pixel  48 . 
     First, the RGB rendering process and the BGR rendering process will be described. Hereinafter, in the (p, q)-th pixel  48   (p,q)  (here, 1≦p≦P 0  and 1≦q≦Q 0 ), the signal value of the rendering input signal of the first sub-pixel is assumed to be x A1−(p,q) , the signal value of the rendering input signal of the second sub-pixel is assumed to be x A2−(p,q) , and the signal value of the rendering input signal of the third sub-pixel is assumed to be x A3−(p,q) . 
       FIG. 13  is a schematic diagram for describing the rendering input signal generated by the RGB rendering process.  FIG. 13  illustrates the rendering input signal value when the RGB rendering process is performed on the input signals of the pixels illustrated in  FIG. 10 . The RGB rendering is a process of changing the input signals gradually in the order of the input signal of the first sub-pixel  49 R, the input signal of the second sub-pixel  49 G, and the input signal of the third sub-pixel  49 B. As illustrated in  FIG. 13 , the RGB rendering process is performed on the pixel  48   (a+1,b)  and the pixel  48   (a+3,b)  to generate the rendering input signal. The input signal values of the sub-pixels of the pixel  48   (a+1,b)  are 255. By performing the RGB rendering process on the pixel  48   (a+1,b) , a first sub-pixel rendering input signal value x A1−(a+1,b)  is 250, a second sub-pixel rendering input signal value x A2−(a+1,b)  is 200, and a third sub-pixel rendering input signal value x A3−(a+1,b)  is 150. Similarly, by performing the RGB rendering process on the pixel  48   (a+3,b) , a first sub-pixel rendering input signal value x 1−(a+3,b)  is 150, a second sub-pixel rendering input signal value x 2−(a+3,b)  is 200, and a third sub-pixel rendering input signal value x 3−(a+3,b)  is 250. The rendering process is not performed on the other pixels. 
     When the RGB rendering process is performed, the rendering input signal values of the pixel  48   (a+1,b)  gradually decrease from the pixel  48   (a,b)  in which the input signal value is 255 toward the pixel  48   (a+2,b)  in which the input signal value is 100 in the order of the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b) . Further, when the RGB rendering process is performed, the rendering input signal values of the pixel  48   (a+3,b)  gradually increase from the pixel  48   (a+2,b)  in which the input signal value is 100 toward the pixel  48   (a+4,b)  in which the input signal value is 255 in the order of the first sub-pixel rendering input signal value x A1−(a+3,b) , the second sub-pixel rendering input signal value x A2−(a+3,b) , and the third sub-pixel rendering input signal value x A3−(a++3,b) . 
     As described above, the RGB rendering process causes the first sub-pixel rendering input signal value x A1−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the input signal value of the sub-pixel of the pixel  48   (a,b)  and the input signal value of the sub-pixel of the pixel  48   (a+2,b) . Further, the RGB rendering process causes the second sub-pixel rendering input signal value x A2−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the first sub-pixel rendering input signal value x A1−(a+1,b)  and the input signal value of the sub-pixel of the pixel  48   (a+2,b) . Furthermore, the RGB rendering process causes the third sub-pixel rendering input signal value x A3−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the second sub-pixel rendering input signal value x A2−(a+1,b)  and the input signal value of the sub-pixel of the pixel  48   (a+2,b) . More specifically, when the input signal value of the sub-pixel of the pixel  48   (a,b)  is larger than the input signal value of the sub-pixel of the pixel  48   (a+2,b) , the RGB rendering process is a process of causing the first sub-pixel rendering input signal value x A1−(a+1,b)  to be largest and causing the third sub-pixel rendering input signal value x A3−(a+1,b)  to be smallest among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b) . 
       FIG. 14  is a schematic diagram for describing the rendering input signals generated by the BGR rendering process.  FIG. 14  illustrates the rendering input signal values when the BGR rendering process is performed on the input signals of the pixels illustrated in  FIG. 10 . The BGR rendering process differs from the RGB rendering process in a change in the input signal values of the sub-pixels  49 . The BGR rendering process gradually changes the input signals in the opposite order to that of the RGB rendering, that is, the order of the input signal of the third sub-pixel  49 B, the input signal of the second sub-pixel  49 G, the input signal of the first sub-pixel  49 R. By performing the BGR rendering process on the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is 150, the second sub-pixel rendering input signal value x A2−(a+1,b)  is 200, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is 250. Similarly, by performing the BGR rendering process on the pixel  48   (a+3,b) , the first sub-pixel rendering input signal value x 1−(a+3,b)  is 250, the second sub-pixel rendering input signal value x 2−(a+3,b)  is 200, and the third sub-pixel rendering input signal value x 3−(a+3,b)  is 150. 
     As described above, the BGR rendering process causes the first sub-pixel rendering input signal value x A1−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the input signal value of the sub-pixel of the pixel  48   (a,b)  and the input signal value of the sub-pixel of the pixel  48   (a+2,b) . Further, the BGR rendering process causes the second sub-pixel rendering input signal value x A2−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the first sub-pixel rendering input signal value x A1−(a+1,b)  and the input signal value of the sub-pixel of the pixel  48   (a,b) . Furthermore, the BGR rendering process causes the third sub-pixel rendering input signal value x A3−(a+1,b)  in the pixel  48   (a+1,b)  to be a value between the second sub-pixel rendering input signal value x A2−(a+1,b)  and the input signal value of the sub-pixel of the pixel  48   (a,b) . More specifically, when the input signal value of the sub-pixel of the pixel  48   (a,b)  is larger than the input signal value of the sub-pixel of the pixel  48   (a+2,b)  the BGR rendering process is a process of causing the first sub-pixel rendering input signal value x A1−(a+1,b)  to be largest and causing the third sub-pixel rendering input signal value x A3−(a+1,b)  to be smallest among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b).    
     The rendering selecting unit  72  selects the RGB rendering process when the sub-pixel arrangement has the first arrangement pattern. The rendering selecting unit  72  selects the BGR rendering process when the sub-pixel arrangement has the second arrangement pattern. The rendering processing unit  74  performs the selected rendering process on the input signal of the pixel  48  decided to undergo the rendering process based on the input signal of each pixel  48 , the rendering position information, and the rendering information. The rendering processing unit  74  performs the selected rendering process on the input signal of the pixel  48  decided to undergo the rendering process, and generates the rendering input signal of the pixel  48  decided to undergo the rendering process. 
     Output Signal Generation Process 
     Next, an output signal generation process of the output processing unit  26  will be described. The output processing unit  26  processes the input signals and the rendering input signals, generates an output signal (a signal value X 1−(p,q) ) of the first sub-pixel for deciding a display gradation of the first sub-pixel  49 R (p,q) , an output signal (the signal value X 2−(p,q) ) of the second sub-pixel for deciding a display gradation of the second sub-pixel  49 G (p,q) , an output signal (the signal value X 3−(p,q) ) of the third sub-pixel  49 B (p,q)  for deciding a display gradation of the third sub-pixel  49 B (p,q) , and an output signal (the signal value X 4−(p,q) ) of the fourth sub-pixel for deciding a display gradation of the fourth sub-pixel  49 W (p,q) , and outputs the output signals to the image display panel driving unit  30 . The output signal generation process of the output processing unit  26  will be described below in detail. 
       FIG. 15  is a conceptual diagram of an extended HSV color space that is extendable by the display device of the first embodiment.  FIG. 16  is a conceptual diagram a relation between a hue and a saturation of the extended HSV color space. In the display device  10 , each of the pixels  48  includes the fourth sub-pixel  49 W that outputs the fourth color (white), and thus the dynamic range of brightness is increased in the extended color space (the HSV color space in the first embodiment) as illustrated in  FIG. 15 . In other words, in the expanded color space extended by the display device  10 , as illustrated in  FIG. 15 , a solid in which a shape in a cross section having a saturation axis and a brightness axis in which as the saturation increases, a maximum value of the brightness decreases is a substantially trapezoidal in which an oblique side is a curve is placed on a cylindrical color space displayable by the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. A maximum value Vmax(S) of the brightness having a saturation S as a variable in the expanded color space (the HSV color space in the first embodiment) expanded by adding the fourth color (white) is stored in the signal processing unit  20 . In other words, the output processing unit  26  stores the value of the maximum value Vmax(S) of the brightness for each coordinate (values) of the saturation and the hue in the three-dimensional shape of the expanded color space illustrated in  FIG. 15 . Since the input signal is configured with input signals for the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B, the color space of the input signal has a cylindrical shape, that is, the same shape as the cylindrical part of the expanded color space. 
     First, the α calculating unit  82  of the output processing unit  26  obtains the saturation S and the brightness V(S) in a plurality of pixels  48  based on the input signal values and the rendering input signal values of the pixels  48  in one frame, and calculates the expansion coefficient α common to all the pixels  48  in one frame. 
     The α calculating unit  82  obtains the saturation S and the brightness V(S) for each of the pixels  48  in one frame. Generally, in the (p, q)-th pixel, a saturation S (p,q)  and the brightness (value) V(S) (p,q ) of an input color in the cylindrical HSV color space are calculated by the following Equations (1) and (2) based on the input signal (the signal value of x 1−(p,q) ) of the first sub-pixel, the input signal (the signal value of x 2−(p,q) ) of the second sub-pixel, and the input signal (the signal value of x 3−(p,q) ) of the third sub-pixel.
 
 S   (p,q) =(Max (p,q) −Min (p,q) )/Max (p,q)   (1)
 
 V ( S ) (p,q) =Max (p,q )  (2)
 
     Max (p,q)  is the maximum value among the input signal values of the three sub-pixels  49 , that is, x 1−(p,q) , x 2−(p,q) , and x 3−(p,q) , and Min (p,q)  is the minimum value among the input signal values of the three sub-pixels  49 , that is, x 1−(p,q) , x 2−(p,q) , and x 3−(p,q) . 
     When the rendering process is performed on the pixel  48   (p,q) , the saturation S (p,q)  and the brightness V(S) (p,q)  are calculated using the rendering input signal values (x A1−(p,q) , x A2−(p,q) , and x A3−(p,q) ) instead of the input signal values (x 1−(p,q) , x 2−(p,q) , and x 3−(p,q) ). 
     The α calculating unit  82  calculates the expansion coefficient α(S) of each pixel  48  based on the brightness V(S) of each pixel  48  and Vmax(S) of the extended color space using the following Equation (3).
 
α( S )= V max( S )/ V ( S )  (3)
 
     The α calculating unit  82  calculates the expansion coefficient α common to all the pixels  48  in one frame based on the expansion coefficients α(S) of all the pixels  48  in one frame. In the first embodiment, a minimum value of the expansion coefficients α(S) of all the pixels  48  in one frame is used as the expansion coefficient α. The α calculating unit  82  may decide the expansion coefficient α so that a percentage of pixels in which a value of extended brightness obtained from a product of the brightness V(S) and the expansion coefficient α exceeds the maximum value Vmax(S) with respect to all pixels is a limit value β or less. Here, the limit value β is an upper limit value (percentage) of a width that exceeds a maximum value of brightness of the extended HSV color space with respect to the maximum value in a value combination of a hue and a saturation. 
     Here, Vmax(S) is a maximum value of brightness that is extendable in the extended color space illustrated in  FIG. 15 . Vmax(S) can be indicated by the following Equations (4) and (5). 
     When S≦S 0 ,
 
 V max( S )=(χ+1)·(2 n −1)  (4)
 
     When S 0 &lt;S≦1,
 
 V max( S )=(2 n −1)·(1/ S )  (5)
 
     Here, S 0 =1/(χ+1) is held. χ will be described later. In the first embodiment, n is assumed to be 8. That is, the display gradation bit number is 8 bits (the display gradation has 256 gradation values, that is, 0 to 255). 
     The output signal generating unit  88  acquires the value of the expansion coefficient α, the rendering input signals of the pixels that have undergone the rendering process, and the input signals of the other pixels from the α calculating unit  82 . The output signal generating unit  88  calculates an output signal value X 4−(p,q)  of the fourth sub-pixel based on at least the input signal (the signal value x 1−(p,q) ) of the first sub-pixel, the input signal (the signal value x 2−(p,q) ) of the second sub-pixel, and the input signal (the signal value x 3−(p,q) ) of the third sub-pixel. More specifically, the output signal generating unit  88  calculates the output signal value X 4−(p,q)  of the fourth sub-pixel based on the product of Min (p,q)  and the expansion coefficient α. Specifically, the signal processing unit  20  may obtain the signal value X 4−(p,q)  based on the following Equation (6). In Equation (6), the product of Min (p,q)  and the expansion coefficient α is divided by χ, but the present invention is not limited thereto.
 
 X   4−(p,q) =Min (p,q) ·α/χ  (6)
 
     When the rendering process is performed on the pixel  48   (p,q) , the output signal value X 4−(p,q)  of the fourth sub-pixel is calculated using the first sub-pixel rendering input signal value x A1−(p,q) , the second sub-pixel rendering input signal value x A2−(p,q) , and the third sub-pixel input signal value x A3−(p,q)  instead of the first sub-pixel input signal value x 1−(p,q) , the second sub-pixel input signal value x 2−(p,q) , and the third sub-pixel input signal value x 3−(p,q) . 
     χ is a constant depending on the display device  10 . No color filter is arranged for the fourth sub-pixel  49 W that displays white. The fourth sub-pixel  49 W that displays the fourth color is higher in brightness than the first sub-pixel  49 R that displays the first color, the second sub-pixel  49 G that displays the second color, and the third sub-pixel  49 B that displays the third color when they are irradiated with light with the same light source lighting amount. When a signal having a value corresponding to the maximum signal value of the output signal of the first sub-pixel  49 R is input to the first sub-pixel  49 R, a signal having a value corresponding to the maximum signal value of the output signal of the second sub-pixel  49 G is input to the second sub-pixel  49 G, and a signal having a value corresponding to the maximum signal value of the output signal of the third sub-pixel  49 B is input to the third sub-pixel  49 B, luminance of an aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B included in the pixel  48  or a group of pixels  48  is assumed to be BN 1-3 . When a signal having a value corresponding to the maximum signal value of the output signal of the fourth sub-pixel  49 W is input to the fourth sub-pixel  49 W included in the pixel  48  or a group of pixels  48 , the luminance of the fourth sub-pixel  49 W is assumed to be BN 4 . That is, white of the maximum luminance is displayed by the aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B, and the luminance of the white is indicated by BN 1-3 . In this case, when χ is a constant depending on the display device  10 , the constant χ is indicated by χ=BN 4 /BN 1-3 . 
     Specifically, the luminance BN 4  when the input signal having the display gradation value of 255 is assumed to be input to the fourth sub-pixel  49 W is, for example, 1.5 times the luminance BN 1-3  of white when the input signals having the display gradation values such as the signal value x 1−(p,q) =255, the signal value x 2−(p,q) =255, and the signal value x 3−(p,q) =255 are input to the aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. That is, in the first embodiment, χ=1.5. 
     Then, the output signal generating unit  88  calculates the output signal (the signal value X 1−(p,q) ) of the first sub-pixel based on at least the input signal of the first sub-pixel (the signal value x 1−(p,q) ) and the expansion coefficient α, calculates the output signal (the signal value X 2−(p,q) ) of the second sub-pixel based on at least the input signal (the signal value x 2−(p,q) ) of the second sub-pixel and the expansion coefficient α, and calculates the output signal (the signal value X 3−(p,q) ) of the third sub-pixel based on at least the input signal (the signal value x 3−(p,q) ) of the third sub-pixel and the expansion coefficient α. 
     Specifically, the output signal generating unit  88  calculates the output signal of the first sub-pixel based on the input signal of the first sub-pixel, the expansion coefficient α, and the output signal of the fourth sub-pixel. The output signal generating unit  88  calculates the output signal of the second sub-pixel based on the input signal of the second sub-pixel, the expansion coefficient α, and the output signal of the fourth sub-pixel. The output signal generating unit  88  calculates the output signal of the third sub-pixel based on the input signal of the third sub-pixel, the expansion coefficient α, and the output signal of the fourth sub-pixel. 
     In other words, the output signal generating unit  88  calculates the output signal value X 1−(p,q)  of the first sub-pixel, the output signal value X 2−(p,q)  of the second sub-pixel, and the output signal value X 3−(p,q)  of the third sub-pixel which are supplied to the (p, q)-th pixel (or the set of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B) using Equations (7) to (9), respectively, when χ is a constant depending on the display device.
 
 X   1−(p,q)   =α·x   1−(p q)   −χ·X   4−(p,q)   (7)
 
 X   2−(p,q)   =α·x   2−(p,q)   −χ·X   4−(p,q)   (8)
 
 X   3−(p,q)   =α·x·x   3−(p,q)   ·χ·X   4−(p,q )  (9)
 
     When the rendering process is performed on the pixel  48   (p,q) , the output signal value X 1−(p,q)  of the first sub-pixel is calculated using the first sub-pixel rendering input signal value x A1−(p,q)  instead of the first sub-pixel input signal value x 1−(p,q)  Similarly, when the rendering process is performed on the pixel  48   (p,q) , the output signal value X 2−(p,q)  of the second sub-pixel is calculated using the second sub-pixel rendering input signal value x A2−(p,q)  instead of the second sub-pixel input signal value x 2−(p,q) . Similarly, when the rendering process is performed on the pixel  48   (p,q) , the output signal value X 3−(p,q)  of the third sub-pixel is calculated using the third sub-pixel rendering input signal value x A3−(p,q)  instead of the third sub-pixel input signal value x 3−(p,q) . 
     The output signal generating unit  88  outputs the output signals of the sub-pixels calculated as described above to the image display panel driving unit  30 . 
     Next, a process of the above-described process operation of the signal processing unit  20  will be described based on a flowchart.  FIG. 17  is a flowchart for describing the process operation of the signal processing unit according to the first embodiment. As illustrated in  FIG. 17 , first, the rendering position deciding unit  21  of the signal processing unit  20  selects the pixel  48  that undergoes the rendering process based on the input signal of each pixel  48  (step S 11 ). When the difference between the input signal values of the sub-pixels  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more, the rendering position deciding unit  21  decides to perform the rendering process on the pixel  48   (a+1,b) . 
     The pattern information acquiring unit  22  of the signal processing unit  20  acquires the pattern information indicating whether the image display panel  40  has the first arrangement pattern or the second arrangement pattern (step S 12 ). In the first embodiment, the display mode deciding unit  13  of the control device  11  determines whether the image display panel  40  has the first arrangement pattern or the second arrangement pattern. For example, in the first landscape mode or the second portrait mode, the display mode deciding unit  13  determines that the image display panel  40  has the first arrangement pattern. Further, for example, in the second landscape mode or the first portrait mode, the display mode deciding unit  13  determines that the image display panel  40  has the second arrangement pattern. 
     After the pattern information acquiring unit  22  acquires the pattern information, the rendering selecting unit  72  of the signal processing unit  20  acquires the pattern information from the pattern information acquiring unit  22 , and when the image display panel  40  has the first arrangement pattern (Yes in step S 14 ), execution of the RGB rendering process is selected (step S 16 ). Further, when the image display panel  40  does not have the first arrangement pattern (No in step S 14 ), that is, when the image display panel  40  has the second arrangement pattern, the rendering selecting unit  72  of the signal processing unit  20  selects execution of the BGR rendering process (step S 18 ). As long as step S 11  is performed before step S 20  which will be described later, step S 11  may be performed before, after, or at the same time as steps S 12 , S 14 , S 16 , and step S 18 . 
     After the pixel  48  that undergoes the rendering process is selected in step S 11 , and execution of the RGB rendering or execution of the BGR rendering is selected in step S 16  or step S 18 , the rendering processing unit  74  of the signal processing unit  20  performs the selected rendering process (the RGB rendering or the BGR rendering) on the input signals of the selected pixel  48 , and generates the rendering input signals of the selected pixel  48  (step S 20 ). 
     After the rendering input signals are generated, the α calculating unit  82  of the signal processing unit  20  calculates the expansion coefficient α common to all the pixels  48  in one frame based on the rendering input signals and the input signals (step S 22 ). The α calculating unit  82  calculates the expansion coefficient α(S) of the pixels based on Equation (3), and decides the minimum value of the expansion coefficients α(S) of all the pixels  48  in one frame as the expansion coefficient α common to all the pixels  48  in one frame. 
     After the expansion coefficient α is calculated, the output signal generating unit  88  of the signal processing unit  20  generates the output signals of the pixels  48  based on the rendering input signals, the input signals, and the expansion coefficient α(step S 24 ). The output signal generating unit  88  calculates the output signal value X 4−(p,q)  of the fourth sub-pixel using Equation (6). Further, the output signal generating unit  88  calculates the output signal value X 1−(p,q)  of the first sub-pixel, the output signal value X 2−(p,q)  of the second sub-pixel, and the output signal value X 3−(p,q)  of the third sub-pixel using Equations (7) to (9). Further, when the rendering process is performed on the pixel  48   (p,q) , the first sub-pixel rendering input signal value x A1−(p,q) , the second sub-pixel rendering input signal value x A2−(p,q) , and the third sub-pixel rendering input signal value x A3−(p,q)  are used instead of the first sub-pixel input signal value x 1−(p,q) , the second sub-pixel input signal value x 2−(p,q) , and the third sub-pixel input signal value x 3−(p,q) . After step S 24 , the current process of the signal processing unit  20  ends. 
     Display Example 
     Next, a display example of the sub-pixels when the rendering process according to the first embodiment is performed will be described. First, a rendering process according to a first comparative example will be described.  FIG. 18  is a schematic diagram illustrating the output signals of the sub-pixels when a rendering process according to the first comparative example is performed. In a display device  10 Y according to the first comparative example, similarly to that of the first embodiment, the display mode (the landscape mode and the portrait mode) is switched. As illustrated in  FIG. 18 , an image display panel  40 Y according to the first comparative example includes a pixel  48 Y (a,b) , a pixel  48 Y (a+1,b) , a pixel  48 Y (a+2,b) , a pixel  48 Y (a+3,b) , and a pixel  48 Y (a+4,b)  which are arranged in the first direction F 1 . The image display panel  40 Y according to the first comparative example has the same sub-pixel arrangement as that of the first embodiment.  FIG. 18  illustrates a sub-pixel arrangement in the first portrait mode. 
     The display device  10 Y according to the first comparative example does not change the rendering process according to the display mode. The display device  10 Y according to the first comparative example performs the RGB rendering even in any display mode. As illustrated in  FIG. 18 , in the first comparative example, since the RGB rendering is performed, the rendering input signal values of the pixels  48 Y according to the first comparative example are the same as those in  FIG. 13 . 
     The display device  10 Y according to the first comparative example generates the output signals based on the input signals and the rendering input signals using the same method as that of the first embodiment. As illustrated in  FIG. 18 , the output signals of the sub-pixels of the pixel  48 Y (a,b)  according to the first comparative example are 180. In the pixel  48 Y (a+1,b) , an output signal value X Y1−(a+1,b)  of the first sub-pixel is 230, an output signal value X Y2−(a+1,b)  of the second sub-pixel is 180, an output signal value X Y3−(a+1,b)  of the third sub-pixel is 110, and an output signal value X Y4−(a+1,b)  of the fourth sub-pixel is 100. The output signals of the sub-pixels of the pixel  48 Y (a+2,b)  are 70. In the pixel  48 Y (a+3,b) , an output signal value X Y1−(a+3,b)  of the first sub-pixel is 110, an output signal value X Y2−(a+3,b)  of the second sub-pixel is 180, an output signal value X Y3−(a+3,b)  of the third sub-pixel is 230, and an output signal value X Y4−(a+3,b)  of the fourth sub-pixel is 100. The output signals of the sub-pixels of the pixel  48 Y (a+4,b)  are 180. 
     Here, a sub-pixel  49 YR and a sub-pixel  49 YW of the pixel  48 Y (a+3,b)  are arranged in the Y direction and have the output signal values of 110 and 100. The sub-pixels adjacent to the sub-pixel  49 YR and the sub-pixel  49 YW of the pixel  48 Y (a+3,b)  in the X direction are a sub-pixel  49 YG and a sub-pixel  49 YB of the pixel  48 Y (a+3,b)  and the sub-pixel  49 YG and the sub-pixel  49 YB of the pixel  48 Y (a+4,b) . The output signal values of the sub-pixel  49 YG and the sub-pixel  49 YB of the pixel  48 Y (a+,b)  are 180 and 230. The output signal values of the sub-pixel  49 YG and the sub-pixel  49 YB of the pixel  48 Y (a+4,b)  are 180. As described above, the sub-pixel  49 YR and the sub-pixel  49 YW of the pixel  48 Y (a+3,b)  are smaller in the output signal value than the sub-pixels adjacent to both the sub-pixels  49 YR and  49 YW in the X direction. For this reason, in the image display panel  40 Y according to the first comparative example, a line L 1  along the Y direction in which the sub-pixel  49 YG and the sub-pixel  49 YB of the pixel  48 Y (a+4,b)  are arranged is darker than a portion therearound and likely to be recognized as a dark line by an observer. As described above, in the display device  10 Y according to the first comparative example, since the rendering process does not change according to the display mode, when the rendering process is performed, the dark line is recognized by the observer, and the deterioration of the image is likely to be recognized. 
       FIG. 19  is a schematic diagram illustrating the output signals of the sub-pixels when the rendering process according to the first embodiment is performed. The display device  10  according to the first embodiment changes the rendering process based on the display mode. In other words, in the display device  10  according to the first embodiment, in the case of the first arrangement pattern, the RGB rendering process is performed, and in the case of the second arrangement pattern, the BGR rendering process is performed.  FIG. 19  illustrates an example in which in the same first portrait mode as in  FIG. 18 , the rendering process according to the first embodiment is performed, and the output signals are displayed. As described above, in the first portrait mode, the signal processing unit  20  according to the first embodiment performs the BGR rendering. As illustrated in  FIG. 19 , the output signals of the sub-pixels of the pixel  48   (a,b) , the pixel  48   (a+2,b) , and the pixel  48   (a+4,b)  have the same values as in the first comparative example illustrated in  FIG. 18 . On the other hand, in the pixel  48   (a+1,b) , an output signal value X 1−(a+1,b)  of the first sub-pixel is 110, an output signal value X 2−(a+1,b)  of the second sub-pixel is 180, an output signal value X 3−(a+1,b)  of the third sub-pixel is 230, and an output signal value X 4−(a+1,b)  of the fourth sub-pixel is 100. Further, in the pixel  48   (a+3,b) , an output signal value X 1−(a+3,b)  of the first sub-pixel is 230, an output signal value X 2−(a+3,b)  of the second sub-pixel is 180, an output signal value X 3−(a+3,b)  of the third sub-pixel is 110, and an output signal value X 4−(a+3,b)  of the fourth sub-pixel is 100. 
     The sub-pixel  49 R and the sub-pixel  49 W of the pixel  48   (a+,b)  have the output signal values of 230 and 100. The output signal values of the second sub-pixel  49 G and the sub-pixel  49 B of the pixel  48   (a+3,b)  are 180 and 110. The output signal values of the second sub-pixel  49 G and the sub-pixel  49 B of the pixel  48   (a+4,b)  are 180. As described above, the sub-pixel  49 R and the sub-pixel  49 W of the pixel  48   (a+3,b)  are suppressed from being smaller in the output signal value than the sub-pixels adjacent to both the sub-pixels  49 R and  49 W in the X direction. Thus, in the image display panel  40  according to the first embodiment, a line L 2  along the Y direction in which the sub-pixel  49 R and the sub-pixel  49 W of the pixel  48   (a+3,b)  are arranged can be suppressed from being recognized as a dark line. As described above, in the display device  10  according to the first embodiment, even when the display mode is switched, it is possible to suppress the deterioration of the image that has undergone the rendering process. 
     As described above, the display device  10  according to the first embodiment includes the image display panel  40  in which a plurality of pixels  48  each of which includes 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 arranged in a 2×2 matrix form are arranged on the display region  43  of the square shape having the first side (the short side  41 ) and the second side (the long side  42 ) in the matrix form. The image display panel  40  receives the image information corresponding to the portrait mode in which the direction along the first side is a predetermined one direction (here, the X direction) of the display image or the landscape mode in which the direction along the second side is a predetermined one direction (here, the X direction) of the display image. The display device  10  further includes the signal processing unit  20  that generates the output signals from the input values of the input signals for the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B, and outputs the generated output signals to the image display panel  40 . The signal processing unit  20  includes the rendering position deciding unit  21  that decides to perform the rendering process on the pixel  48   (a+1,b)  when, in the pixel  48   (a,b) , the pixel  48   (a+1,b) , and the pixel  48   (a+2,b)  arranged in the processing direction (here, the first direction F 1 ) among the pixels  48 , the difference between the input signal values of the sub-pixels  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more. The signal processing unit  20  further includes the pattern information acquiring unit  22  that acquires the arrangement of the sub-pixels  49  in the processing direction (here, the first direction F 1 ) of the display mode of either of the portrait mode and the landscape mode as the pattern information indicating either of the first arrangement pattern and the second arrangement pattern that differ in the arrangement of the sub-pixels  49 . The signal processing unit  20  further includes the rendering unit  24  that performs the first sub-pixel rendering process (the RGB rendering process) or the second sub-pixel rendering process (the BGR rendering process) on the input signals of the sub-pixels of the pixel  48   (a+1,b)  based on the decision of the rendering position deciding unit  21  and the pattern information, and generates the rendering input signals of the sub-pixels of the pixel  48   (a+1,b) . Here, the processing direction (here, the first direction F 1 ) is the direction along the first side (the short side  41 ) of the display region  43  when the display mode is the portrait mode and the direction along the second side (the long side  42 ) of the display region  43  when the display mode is the landscape mode. 
     In the display device  10 , the sub-pixels  49  are arranged in a diagonal form of a 2×2 matrix, and the RGB rendering or the BGR rendering is selected according to whether the image display panel  40  has the first arrangement pattern or the second arrangement pattern. Since the display device  10  can perform the rendering process according to the display mode, even when the display mode is switched, for example, it is possible to suppress a black line from being recognized and suppress the deterioration of the image. 
     Here, in the case of the first arrangement pattern, the second sub-pixel  49 G belonging to the same pixel  48  is adjacent to the side of the first sub-pixel  49 R in the processing direction (the first direction F 1 ), and the third sub-pixel  49 B belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (the first direction F 1 ). In the case of the second arrangement pattern, the first sub-pixel  49 R belonging to the same pixel  48  is adjacent to the side of the second sub-pixel  49 G in the processing direction (the first direction F 1 ), or the second sub-pixel  49 G belonging to the same pixel  48  is adjacent to the side of the third sub-pixel  49 B in the processing direction (the first direction F 1 ). The rendering unit  72  performs the RGB rendering in the case of the first arrangement pattern, and performs the BGR rendering process in the case of the second arrangement pattern. When the RGB rendering is performed in the case of the first arrangement pattern, and the BGR rendering is performed in the case of the second arrangement pattern, for example, a black line can be suppressed from being recognized. Thus, the display device  10  can appropriately suppress the deterioration of the image. 
     Here, when the input signal values of the sub-pixels of the pixel  48   (a,b)  are larger than the input signal values of the sub-pixels of the pixel  48   (a+2,b) , the RGB rendering process causes the first sub-pixel rendering input signal value x A1−(a+1,b)  to be largest and causes the third sub-pixel rendering input signal value x A3−(a+1,b)  to be smallest among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) . Further, the BGR rendering process causes the first sub-pixel rendering input signal value x A1−(a+1,b)  to be smallest and causes the third sub-pixel rendering input signal value x A3−(a+1,b)  to be largest among the first sub-pixel rendering input signal value x A1−(a+1,b)  the second sub-pixel rendering input signal value X A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) . The display device  10  gradually changes the output signal of the sub-pixel according to the output signal of the neighboring sub-pixel and thus can make the display image smooth. 
     A relation among the display mode, the arrangement pattern, and the rendering process in the image display panel according to the first embodiment is described below.  FIG. 20A  is a table indicating a relation among the display mode, the arrangement pattern, and the rendering process in the image display panel according to the first embodiment. As illustrated in  FIG. 20A , when the image display panel  40  displays the image in the first portrait mode, the sub-pixel arrangement has the second arrangement pattern, and the BGR rendering is selected. Further, when the image display panel  40  displays the image in the first landscape mode, the sub-pixel arrangement has the first arrangement pattern, and the RGB rendering is selected. When the image display panel  40  displays the image in the second portrait mode, the sub-pixel arrangement has the first arrangement pattern, and the RGB rendering is selected. When the image display panel  40  displays the image in the second landscape mode, the sub-pixel arrangement has the second arrangement pattern, and the BGR rendering is selected. 
     The image display panel with which the display device  10  is equipped is not limited to the image display panel  40  having the sub-pixel arrangement illustrated in  FIG. 20A . The image display panel with which the display device  10  is equipped may differ in the sub-pixel arrangement from the image display panel  40  when the display mode is fixed as long as 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  are arranged in the 2×2 matrix.  FIG. 20B  is a table indicating a relation among the display mode, the arrangement pattern, and the rendering process in another example of the image display panel according to the first embodiment.  FIG. 20B  illustrates a relation among the display mode, the arrangement pattern, and the rendering process in an image display panel  40 S that differs in the sub-pixel arrangement from the image display panel  40 . Here, the row direction is assumed to be the processing direction, and a direction orthogonal to the processing direction is assumed to an orthogonal direction. As illustrated in  FIG. 20B , each of pixels  48 S arranged in the image display panel  40 S includes a second sub-pixel  49 G arranged in the first row of the first column, a first sub-pixel  49 R arranged in the second row of the first column, a third sub-pixel  49 B arranged in the first row of the second column, and a fourth sub-pixel  49 W arranged in the second row of the second column in the first portrait mode. When the image display panel  40 S displays the image in the first portrait mode, the sub-pixel arrangement has the first arrangement pattern, and the RGB rendering is selected. When the image display panel  40 S displays the image in the first landscape mode, the sub-pixel arrangement has the second arrangement pattern, and the BGR rendering is selected. When the image display panel  40 S displays the image in the second portrait mode, the sub-pixel arrangement has the second arrangement pattern, and the BGR rendering is selected. When the image display panel  40 S displays the image in the second landscape mode, the sub-pixel arrangement has the first arrangement pattern, and the RGB rendering is selected. 
     The display device  10  may include the above-described image display panel  40 S. Specifically, the display device  10  may include the image display panel having the sub-pixel arrangement different from those of the image display panels  40  and  40 S as long as 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  are arranged in the 2×2 matrix. Regardless of the sub-pixel arrangement of the image display panel  40  with which the display device  10  is equipped, in a first arrangement mode, it is desirable that the second sub-pixel  49 G belonging to the same pixel  48  be adjacent to the side of the first sub-pixel  49 R in the processing direction, or the third sub-pixel  49 B belonging to the same pixel  48  be adjacent to the side of the second sub-pixel  49 G in the processing direction. Further, in a second arrangement mode, it is desirable that the first sub-pixel  49 R belonging to the same pixel  48  be adjacent to the side of the second sub-pixel  49 G in the processing direction, or the second sub-pixels  49 G belonging to the same pixel  48  be adjacent to the side of the third sub-pixel  49 B in the processing direction. Here, an arrangement in which the first sub-pixel  49 R and the second sub-pixel  49 G are arranged in the processing direction in this order is referred to as an “RG arrangement,” and an arrangement in which the second sub-pixel  49 G and the third sub-pixel  49 B are arranged in the processing direction in this order is referred to as a “GB arrangement.” Further, an arrangement in which the second sub-pixel  49 G and the first sub-pixel  49 R are arranged in the processing direction in this order is referred to as a “GR arrangement,” and an arrangement in which the third sub-pixel  49 B and the second sub-pixel  49 G are arranged in the processing direction in this order is referred to as a “BG arrangement.” The display device  10  may select the RGB rendering in the case of either the RG arrangement or the GB arrangement and select the BGR rendering in the case of either the GR arrangement or the BG arrangement. 
     Second Embodiment 
     Next, a second embodiment will be described. A display device  10 A according to the second embodiment (a second aspect) differs from that of the first embodiment in that a correction process is performed on the rendering input signal of the fourth sub-pixel according to the pattern information while performing a predetermined rendering process. In a configuration of the display device  10 A according to the second embodiment, a description of portions common to those of the first embodiment will be omitted. 
     Configuration of Signal Processing Unit 
       FIG. 21  is a block diagram illustrating a configuration of a signal processing unit according to the second embodiment. As illustrated in  FIG. 21 , a signal processing unit  20 A according to the second embodiment includes a pattern information acquiring unit  22 A, a rendering unit  24 A, a correction process deciding unit  76 A, an α calculating unit  82 A, a W generation signal unit  83 A (a fourth sub-pixel generation signal unit), a W output signal generating unit  84 A (a fourth sub-pixel output signal generating unit), and an output signal generating unit  88 A. 
     As described above, the display mode deciding unit  13  of the control device  11  decides the display mode to which the image display panel  40  is set among the first portrait mode, the second portrait mode, the first landscape mode, and the second landscape mode. The pattern information acquiring unit  22 A acquires the pattern information from the display mode deciding unit  13 . In the second embodiment, in addition to the information indicating the first arrangement pattern or the second arrangement pattern, the pattern information includes information indicating whether or not the third sub-pixel  49 B and the fourth sub-pixel  49 W in the same pixel  48  are arranged in the first direction F 1  in the corresponding display mode. In the second embodiment, the information indicating whether or not the third sub-pixel  49 B and the fourth sub-pixel  49 W in the same pixel  48  are arranged in the first direction F 1  is information indicating the first BW arrangement or the second BW arrangement. The first BW arrangement is a sub-pixel arrangement in which the third sub-pixel  49 B and the fourth sub-pixel  49 W in the same pixel  48  are arranged in the first direction F 1  (the processing direction) (adjacent to each other in the first direction F 1 ) in the image display panel  40 . The second BW arrangement is a sub-pixel arrangement in which the third sub-pixel  49 B and the fourth sub-pixel  49 W in the same pixel  48  are not arranged in the first direction F 1  (the processing direction) (not adjacent to each other in the first direction F 1 ) in the image display panel  40 . The second BW arrangement information indicates that the third sub-pixel  49 B and the fourth sub-pixel  49 W in the same pixel  48  are arranged in a direction orthogonal to the first direction F 1  (adjacent to each other in the direction orthogonal to the first direction F 1 ). 
     As described above, the pattern information according to the second embodiment includes the information indicating the first arrangement pattern or the second arrangement pattern and the information indicating the first BW arrangement or the second BW arrangement. The pattern information according to the second embodiment is uniquely decided according to the information of the display mode. In other words, when the image display panel  40  is in the first portrait mode, the image display panel  40  has the second arrangement pattern and the first BW arrangement (see  FIG. 20A ). When the image display panel  40  is in the second portrait mode, the image display panel  40  has the first arrangement pattern and the first BW arrangement (see  FIG. 20A ). When the image display panel  40  is in the first landscape mode, the image display panel  40  has the first arrangement pattern and the second BW arrangement. When the image display panel  40  is in the second landscape mode, the image display panel  40  has the second arrangement pattern and the second BW arrangement (see  FIG. 20A ). In other words, the pattern information according to the second embodiment is the information of the display mode (the first portrait mode, the second portrait mode, the first landscape mode, or the second landscape mode). The pattern information acquiring unit  22 A may acquire the information of the display mod (the first portrait mode, the second portrait mode, the first landscape mode, or the second landscape mode) from the display mode deciding unit  13  instead of the pattern information. 
     The rendering unit  24 A includes a rendering position deciding unit  21  and a rendering processing unit  74 A. The rendering processing unit  74 A performs a predetermined rendering process on the pixel  48  decided to undergo the rendering process by the rendering position deciding unit  21 , and generates the rendering input signal. In the second embodiment, the rendering processing unit  74 A performs the RGB rendering process. The rendering processing unit  74 A may perform the BGR rendering process or may perform any one of the RGB rendering and the BGR rendering. 
     The correction process deciding unit  76 A acquires the pattern information from the pattern information acquiring unit  22 A. The correction process deciding unit  76 A acquires the rendering input signal from the rendering processing unit  74 A. The correction process deciding unit  76 A decides whether or not a fourth sub-pixel output signal of the pixel  48  that has undergone the rendering process is generated through the correction process based on the pattern information and the rendering input signal. The correction process deciding unit  76 A outputs correction decision information which includes information indicating whether or not the correction process is performed to the W generation signal unit  83 A. A method of deciding whether or not the correction process is performed will be described later. 
     The α calculating unit  82 A calculates the expansion coefficient α based on the rendering input signal of the pixel  48  that has undergone the rendering process and the input signals of the other pixels using the same method as in the first embodiment. The α calculating unit  82 A outputs the rendering input signal, and the information of the expansion coefficient α to the W generation signal unit  83 A. 
     When the correction process is decided to be performed, the W generation signal unit  83 A generates a fourth sub-pixel generation signal of the pixel  48  that has undergone the rendering process based on the correction decision information, the rendering input signal, and the expansion coefficient α. A process of generating the fourth sub-pixel generation signal will be described later. 
     The W output signal generating unit  84 A generates the fourth sub-pixel output signal of the pixel  48  that has undergone the rendering process, based on the rendering input signal and the fourth sub-pixel generation signal of the pixel  48  that has undergone the rendering process. The fourth sub-pixel output signal generation process will be described later. 
     The output signal generating unit  88 A generates the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48  that has undergone the rendering process, based on the fourth sub-pixel output signal and the rendering input signal. The output signal generating unit  88 A generates the output signals of the sub-pixels based on the input signals of the other pixels  48 . The output signal generation process will be described later. 
     Process Operation of Signal Processing Unit 
     Next, process operations of the respective units of the signal processing unit  20 A will be described in detail. The process operation of the rendering position deciding unit  21  is the same as that of the first embodiment. The rendering process of the rendering processing unit  74 A is the same as the RGB rendering in the first embodiment. A process of the pattern information acquiring unit  22  is the same as that of the first embodiment. 
     The correction process deciding unit  76 A acquires the pattern information from the pattern information acquiring unit  22 . The correction process deciding unit  76 A acquires the rendering input signal. The correction process deciding unit  76 A decides the pixel that undergoes the correction process based on the pattern information and the rendering input signal. In further detail, the correction process deciding unit  76 A decides the pixel that undergoes the correction process based on the pattern information and a magnitude relation among the rendering input signal values of the sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B) in the same pixel  48 . 
     Specifically, when the image display panel  40  has the second arrangement pattern and the first BW arrangement (is in the first portrait mode according to the present embodiment), if, among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is smallest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is largest, the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (a+1,b) . 
     Further, when the image display panel  40  has the second arrangement pattern and the second BW arrangement (is in the second landscape mode in the present embodiment), if, among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest, the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (a+1,b) . 
     Further, when the BGR rendering is performed, the correction process deciding unit  76 A decides that the correction process is performed for the following case. When the image display panel  40  has the first arrangement pattern and the first BW arrangement (is in the second portrait mode in the present embodiment), if, among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is smallest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is largest, the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (a+1,b) . 
     Further, when the BGR rendering is performed, and the image display panel  40  has the first arrangement pattern and the second BW arrangement (is in the first landscape mode in the present embodiment), if, among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest, the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (a+1,b) . 
     When the correction process is decided to be performed, the W generation signal unit  83 A generates the fourth sub-pixel generation signal of the pixel  48  that has undergone the rendering process. Here, an example in which the rendering process is performed on the pixel  48   (a+1,b) , and the correction process is decided to be performed will be described. The W generation signal unit  83 A calculates a fourth sub-pixel generation signal value X A4−(a+1,b)  of the pixel  48   (a+1,b)  using the following Equation (10).
 
 X   A4−(a+1,b) =Min (a+1,b)·α/χ   (10)
 
     Here, Min (a+1,b)  is a minimum value among a first sub-pixel rendering input signal value x A1−(a+1,b) , a second sub-pixel rendering input signal value x A2−(a+1,b) , and a third sub-pixel input signal value x A3−(a+1,b) . In other words, the fourth sub-pixel generation signal value X A4−(a+1,b)  is calculated using the same method as that for the fourth sub-pixel output signal according to the first embodiment. 
     The W output signal generating unit  84 A generates the output signal of the fourth sub-pixel for the pixel  48   (a+1,b)  for which the fourth sub-pixel generation signal is generated. The W output signal generating unit  84 A performs the correction process by performing an averaging process of averaging the fourth sub-pixel generation signal value X A4−(a+1,b)  and the values based on the input signal values of the other sub-pixel  49 , so as to calculate the fourth sub-pixel output signal value X 4−(a+1,b)  of the pixel  48   (a+1,b) . Specifically, the W output signal generating unit  84 A calculates the fourth sub-pixel output signal value X 4−(a+1,b)  of the pixel  48   (a+1,b)  based on the following Equation (11).
 
 X   4−(a+1,b) =( a·x   A4−(a+1,b)   b ·Max (a+1,b) /( a+b )  (11)
 
     Here, Max (a+1,b)  is a maximum value of the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel input signal value x A3−(a+1,b) . Further, “a” and “b” are arbitrary coefficients, and both “a” and “b” are 1 in the second embodiment. The W output signal generating unit  84 A calculates the fourth sub-pixel output signal value X 4−(a+1,b)  of the pixel  48   (a+1,b)  by averaging the fourth sub-pixel generation signal value X A4−(a+1,b)  of the pixel  48   (a+1,b)  and the maximum value of the rendering input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48   (a+1,b) . In Equation (11), arithmetic averaging is performed, but an embodiment is not limited thereto, and an arbitrary averaging process such as geometric averaging may be performed. The W output signal generating unit  84 A performs the averaging process using Mid (a+1,b)  instead of Max (a+1,b) . Mid (a+1,b)  is an intermediate value (a value that is neither the maximum value nor the minimum value) of the rendering input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48   (a+1,b) . The W output signal generating unit  84 A may perform the averaging process using the average value of the rendering input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48   (a+1,b)  instead of Max (a+1,b) . The W output signal generating unit  84 A may perform the averaging process based on any one of the first sub-pixel input signal value x 1−(a+1,b) , the second sub-pixel input signal value x 2−(a+1,b) , and the third sub-pixel input signal value x 3−(a+1,b)  as long as the fourth sub-pixel output signal value X 4−(a+1,b)  is larger than the fourth sub-pixel generation signal value X A4−(a+1,b) . 
     Further, the W output signal generating unit  84 A may calculate a first sub-pixel generation signal value X A1−(a+1,b)  a second sub-pixel generation signal value X A2−(a+1,b)  and a third sub-pixel generation signal value X A3−(a+1,b)  of the pixel  48   (a+1,b)  using the following Equations (12) to (14) and perform the averaging process using these values. For example, the W output signal generating unit  84 A may perform the averaging process using the fourth sub-pixel generation signal value X A4−(a+1,b)  and the maximum value or the intermediate value of X A1−(a+1,b) , X A2−(a+1,b) , and X A3−(a+1,b)  so as to calculate the fourth sub-pixel output signal value X 4−(a+1,b) .
 
 X   A1−(a+1,b)   =α·x   A1−(a+1,b)   χ·X   4−(a+1,b)   (12)
 
 X   A2−(a+1,b)   =α·x   A2−(a+1,b)   χ·X   4−(a+1,b)   (13)
 
 X   A3−(a+1,b)   =α·x   A3−(a+1,b)   −χ·X   4−(a+1,b)   (14)
 
     The output signal generating unit  88 A generates the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48   (a+1,b)  that has undergone the correction process. The output signal generating unit  88 A generates the output signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel of the other pixels  48 . The output signal generation process is the same as that of the first embodiment. 
     Next, the rendering process of the rendering processing unit  74 A and a process of the correction process decision operation by the correction process deciding unit  76 A will be described using flowcharts.  FIG. 22A  is a flowchart for describing process operations of the rendering processing unit and the correction process deciding unit according to the second embodiment. As illustrated in  FIG. 22A , first, the rendering processing unit  74 A performs the RGB rendering process, and generates the rendering input signal (step S 32 A). 
     After the rendering input signal is generated, the correction process deciding unit  76 A acquires the pattern information from the pattern information acquiring unit  22 , and when the image display panel  40  has the second arrangement pattern (Yes in step S 34 A), and the image display panel  40  has the first BW arrangement (Yes in step S 36 A), the correction process deciding unit  76 A determines whether or not the rendering input signal value of the pixel  48   (p,q)  satisfies a relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  (step S 38 A). The relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  refers to a relation in which, among the first sub-pixel rendering input signal value x A1−(p,q) , the second sub-pixel rendering input signal value x A2−(p,q) , the third sub-pixel rendering input signal value x A3−(p,q)  of the pixel  48   (p,q) , the first sub-pixel rendering input signal value x A1−(p,q)  is smallest, and the third sub-pixel rendering input signal value x A3−(p,q)  is largest. 
     When the image display panel  40  has the second arrangement pattern and the first BW arrangement, and the relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  is satisfied (Yes in step S 38 A), the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (p,q)  satisfying the relation (step S 40 A). The correction process is a process of generating the fourth sub-pixel output signal based on the fourth sub-pixel generation signal using Equations (10) and (11). 
     When the image display panel  40  has the second arrangement pattern and the first BW arrangement, but the pixel  48   (p,q)  does not satisfy the relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  (No in step S 38 A), the correction process deciding unit  76 A decides not to perform the correction process on the pixel  48   (p,q)  (step S 41 A). 
     Further, when the image display panel  40  is determined not to have the first BW arrangement, that is, determined to have the second BW arrangement in step S 36 A (No in step S 36 A), the correction process deciding unit  76 A determines whether or not the rendering input signal value of the pixel  48   (p,q)  satisfies the relation of x A1−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  (step S 42 A). The relation of x A1−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  refers to a relation in which, among the first sub-pixel rendering input signal value x A1−(p,q) , the second sub-pixel rendering input signal value x A2−(p,q) , and the third sub-pixel rendering input signal value x A3−(p,q)  of the pixel  48   (p,q) , the first sub-pixel rendering input signal value X A1−(p,q)  is largest, and the third sub-pixel rendering input signal value x A3−(p,q)  is smallest. 
     When the image display panel  40  has the second arrangement pattern but does not have the first BW arrangement (has the second BW arrangement), and the relation of x A−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  is satisfied (Yes in step S 42 A), the correction process deciding unit  76 A decides to perform the correction process on the pixel  48   (p,q)  satisfying the relation (step S 43 A). 
     When the image display panel  40  has the second arrangement pattern but does not have the first BW arrangement (has the second BW arrangement), and the pixel  48   (p,q)  does not satisfy the relation of x A−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  (No in step S 42 A), the correction process deciding unit  76 A decides not to perform the correction process on the pixel  48   (p,q)  (step S 44 A). 
     Further, when the image display panel  40  does not have the second arrangement pattern (No in step S 34 A), that is, when the image display panel  40  has the first arrangement pattern, the correction process deciding unit  76 A decides not to perform the correction process on all the pixels  48  in one frame (step S 46 A). After the process of any one of steps S 40 A, S 41 A, S 43 A, S 44 A, and S 46 A is performed, the current process ends. 
     Further, when the BGR rendering process is performed, the correction process decision flow differs from that of  FIG. 22A .  FIG. 22B  is a flowchart for describing process operations of the rendering processing unit and the correction process deciding unit according to another example of the second embodiment.  FIG. 22B  illustrates the correction process decision flow when the BGR rendering process is performed. In this case, as illustrated in  FIG. 22B , the rendering processing unit  74 A performs the BGR rendering process, and generates the rendering input signal (step S 32 B). 
     After the rendering input signal is generated, the correction process deciding unit  76 A acquires the pattern information from the pattern information acquiring unit  22 , and determines whether or not the image display panel  40  has the first arrangement pattern (step S 34 B). When the image display panel  40  has the first arrangement pattern (Yes in step S 34 B), the correction process deciding unit  76 A performs step S 36 B. A subsequent process including step S 36 B, that is, steps S 36 B, S 38 B, S 40 B, S 41 B, S 42 B, S 43 B, and S 44 B have the same processing content as steps S 36 A, S 38 A, S 40 A, S 41 A, S 42 A, S 43 A, and S 44 A of  FIG. 22A , and thus a description thereof is omitted. Further, when the image display panel  40  does not have the first arrangement pattern (No in step S 34 B), the correction process deciding unit  76 A decides not to perform the correction process on all the pixels  48  in one frame (step S 46 B). After the process of any one of steps S 40 B, S 41 B, S 43 B, S 44 B, and S 46 B is performed, the current process ends. 
     Display Example 
     Next, a display example of the sub-pixels when the rendering process and the correction process according to the second embodiment are performed will be described. As described above with reference to  FIG. 18 , the display device  10 Y according to the first comparative example does not change the rendering process according to the display mode and does not perform the correction process described in the second embodiment, and thus the line L 1  of  FIG. 18  is likely to be recognized as the dark line when the rendering process is performed. 
       FIG. 23A  is a schematic diagram illustrating an example of the output signals of the sub-pixels when the rendering process and the correction process according to the second embodiment are performed. In the example illustrated in  FIG. 23A , the image display panel  40  is assumed to be in the first portrait mode. As illustrated in  FIG. 23A , in the second embodiment, similarly to the first comparative example, the RGB rendering process is performed even in the first portrait mode. Here, as described above, in the first portrait mode, the image display panel  40  has the second arrangement pattern and the first BW arrangement. Further, as illustrated in  FIG. 23A , among the rendering input signal values of the pixel  48   (a+3,b)  the first sub-pixel rendering input signal value x A1−(a+3,b)  is smallest, and the third sub-pixel rendering input signal value x A3−(a+3,b)  is largest. Thus, the signal processing unit  20 A according to the second embodiment performs the correction process on the pixel  48   (a+3,b) . In other words, the signal processing unit  20 A generates the fourth sub-pixel generation signal for the pixel  48   (a+3,b) , and generates the fourth sub-pixel output signal by performing the averaging process using the fourth sub-pixel generation signal value X A4−(a+3,b)  and Max (a+3,b) . On the other hand, among the rendering input signal values of the pixel  48   (a+1,b)  the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest. Thus, the signal processing unit  20 A according to the second embodiment does not perform the correction process on the pixel  48   (a+1,b) . 
     As illustrated in  FIG. 23A , in the pixel  48   (a+3,b)  that has undergone the correction process, an output signal value X 1−(a+3,b)  of the first sub-pixels is 43, an output signal value X 2−(a+3,b)  of the second sub-pixel is 115, an output signal value X 3−(a+3,b)  of the third sub-pixel is 188, and an output signal value X 4−(a+3,b)  of the fourth sub-pixel is 175. In the pixel  48   (a+3,b) , the output signal value X 4−(a+3,b)  of the fourth sub-pixel is increased through the correction process. The display device  10 A according to the second embodiment can increase luminance of a line L 3 A along the Y direction in which the sub-pixel  49 R and the sub-pixel  49 W of the pixel  48   (a+3,b)  are arranged by increasing the output value of the sub-pixel  49 W of the pixel  48   (a+3,b) . Thus, the display device  10 A can suppress, for example, the black line from being recognized and suppress the deterioration of the image. Further, the display device  10 A does not perform the correction process on the pixel  48   (a+1,b)  in which the black line is unlikely to be recognized. Thus, the display device  10 A can suppress the deterioration of the image such as recognition of the black line and can smoothly display the image by appropriately performing the rendering process. 
       FIG. 23B  is a schematic diagram illustrating another example of the output signals of the sub-pixels when the rendering process and the correction process according to the second embodiment are performed. In the example illustrated in  FIG. 23B , the image display panel  40  is assumed to be in the second landscape mode. As illustrated in  FIG. 23B , the display device  10 Y according to the first comparative example does not change the rendering process according to the display mode and does not perform the correction process described in the second embodiment. Here, as described above, in the second landscape mode, the image display panel  40  has the second arrangement pattern and the second BW arrangement. Further, as illustrated in  FIG. 23B , among the rendering input signal values of the pixel  48   (a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest. Thus, the signal processing unit  20 A according to the second embodiment performs the correction process on the pixel  48   (a+1,b) . In other words, the signal processing unit  20 A generates the fourth sub-pixel generation signal on the pixel  48   (a+1,b) , and generates the fourth sub-pixel output signal by performing the averaging process using the fourth sub-pixel generation signal value X A4−(a+1,b)  and Max (a+1,b) . On the other hand, among the rendering input signal values of the pixel  48   (a+3,b) , the first sub-pixel rendering input signal value x A1−(a+3,b)  is smallest, the third sub-pixel rendering input signal value x A3−(a+3,b)  is largest. Thus, the signal processing unit  20 A according to the second embodiment does not perform the correction process on the pixel  48   (a+3,b) . 
     As illustrated in  FIG. 23B , in the first comparative example, the sub-pixel  49 YB and the sub-pixel  49 YW in the pixel  48 Y (a+1,b)  are arranged in the Y direction (the direction orthogonal to the first direction F 1 ) and have the signal values of 110 and 100. Thus, in the image display panel  40 Y according to the first comparative example, in the second landscape mode, the sub-pixel  49 YB and the sub-pixel  49 YW in the pixel  48 Y (a+1,b)  are smaller in the signal value than the sub-pixels adjacent to both sides in the X direction, and a line L 3 B formed by the sub-pixel  49 YB and the sub-pixel  49 YW is likely to be recognized as the dark line. 
     On the other hand, when the correction process according to the second embodiment is performed, in the pixel  48   (a+1,b)  that has undergone the correction process, the output signal value X 1−(a+1,b)  of the first sub-pixel is 188, the output signal value X 2−(a+1,b)  of the second sub-pixel is 115, the output signal value X 3−(a+1,b)  of the third sub-pixel is 43, and the output signal value X 4−(a+1,b)  of the fourth sub-pixel is 175. In the pixel  48   (a+1,b)  the output signal value X 4−(a+1,b)  of the fourth sub-pixel is increased through the correction process. The display device  10 A according to the second embodiment can increase luminance of a line L 3 C along the Y direction in which the sub-pixel  49 B and the sub-pixel  49 W of the pixel  48   (a+1,b)  are arranged by increasing the output value of the sub-pixel  49 W of the pixel  48   (a+1,b) . Thus, the display device  10 A can suppress, for example, the black line from being recognized and suppress the deterioration of the image. Further, the display device  10 A does not perform the correction process on the pixel  48   (a+3,b)  in which the black line is unlikely to be recognized. Thus, the display device  10 A can suppress the deterioration of the image such as the recognition of the black line and can smoothly display the image by appropriately performing the rendering process. 
     As described above, the display device  10 A according to the second embodiment includes the image display panel  40  in which a plurality of pixels  48  each of which includes 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 arranged in a 2×2 matrix form are arranged on the display region  43  of the square shape having the first side (the short side  41 ) and the second side (the long side  42 ) in the matrix form. The image display panel  40  receives the image information corresponding to the portrait mode in which the direction along the first side is a predetermined one direction (here, the X direction) of the display image or the landscape mode in which the direction along the second side is a predetermined one direction (here, the X direction) of the display image. The signal processing unit  20 A according to the second embodiment includes the rendering unit  24 A that performs the rendering process on the pixel  48   (a+1,b) , the pixel  48   (a,b) , the pixel  48   (a+1,b) , and the pixel  48   (a+2,b)  arranged in the processing direction (here, the first direction F 1 ), when the difference between the input signal values of the sub-pixel  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more. The signal processing unit  20 A further includes the pattern information acquiring unit  22  that acquires the arrangement of the sub-pixels  49  in the processing direction (here, the first direction F 1 ) of the display mode of either of the portrait mode and the landscape mode as the pattern information indicating either of the first arrangement pattern and the second arrangement pattern that differ in the arrangement of the sub-pixels  49 . The signal processing unit  20 A further includes the correction process deciding unit  76 A that decides whether or not the output signal of the fourth sub-pixel in the pixel  48   (a+1,b)  is generated through the correction process based on the pattern information. The signal processing unit  20 A includes the W generation signal unit  83 A that obtains the fourth sub-pixel generation signal in the pixel  48   (a+1,b)  based on the rendering input signals of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48   (a+1,b) , and the expansion coefficient α, based on the decision of the correction process deciding unit  76 A. The signal processing unit  20 A further includes the W output signal generating unit  84 A that performs the correction process by performing the averaging process based on the fourth sub-pixel generation signal in the pixel  48   (a+1,b)  and the input signal of the other sub-pixels  49 , and generates the fourth sub-pixel output signal in the pixel  48   (a+1,b) . The signal processing unit  20 A further includes the output signal generating unit  88 A that generates the output signals of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48   (a+1,b) . 
     In the display device  10 A, the sub-pixels  49  are arranged in a diagonal form of a 2×2 matrix The output signal value of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process is increased by performing the correction process on the pixel  48  that has undergone the rendering process according to whether the image display panel  40  has the first arrangement pattern or the second arrangement pattern. Since the display device  10 A can increase the luminance of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process according to the display mode, even when the display mode is switched, for example, it is possible to suppress the black line from being recognized and suppress the deterioration of the image. 
     Further, when the rendering process to be performed is the RGB rendering process, the display device  10 A performs the correction process on a predetermined pixel  48  in the case of the second arrangement pattern. Further, when the rendering process to be performed is the BGR rendering process, the display device  10 A performs the correction process on a predetermined pixel  48  in the case of the first arrangement pattern. Thus, for example, when the black line is likely to be recognized, the display device  10 A can appropriately increase the luminance of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process. Thus, the display device  10 A can appropriately suppress the deterioration of the image. 
     In addition, when the rendering process to be performed is the RGB rendering process, and the image display panel  40  has the second arrangement pattern, the display device  10 A selects a predetermined pixel  48  that undergoes the correction process based on the magnitude relation of the rendering input signal values among the sub-pixels  49  in the same pixel  48 . For example, when the RGB rendering process is performed, and the image display panel  40  has the second arrangement pattern and the first BW arrangement, the display device  10 A performs the correction process on the pixel  48   (a+3,b)  in which, among the first sub-pixel rendering input signal value x A1−(a+3,b) , the second sub-pixel rendering input signal value x A2−(a+3,b) , the third sub-pixel rendering input signal value x A3−(a+3,b) , the first sub-pixel rendering input signal value x A1−(a+3,b)  is smallest, and the third sub-pixel rendering input signal value x A3−(a+3,b)  is largest. Further, when the RGB rendering process is performed, and the image display panel  40  has the second arrangement pattern and the second BW arrangement, the display device  10 A performs the correction process on the pixel  48   (a+1,b)  in which, among the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest, and the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest. 
     Thus, the display device  10 A can appropriately suppress the deterioration of the image by increasing the luminance of the fourth sub-pixel  49 W, for example, for the pixel in which the black line is likely to be recognized. Further, the display device  10 A performs the correction process on only on the pixel  48  satisfying the conditions and does not perform the correction process on the other pixels  48 . Thus, the display device  10 A performs the correction process on only on the pixel in which the black line is likely to be recognized and thus can smoothly display the image by appropriately performing the rendering process while suppressing the deterioration of the image such as the recognition of the black line. However, when the rendering process to be performed is the RGB rendering process, in the case of the second arrangement pattern, the display device  10 A may perform the correction process on all the pixels  48  that have undergone the rendering process. 
     Further, when the rendering process to be performed is the BGR rendering process, and the image display panel  40  has the first arrangement pattern, the display device  10 A selects a predetermined pixel  48  that undergoes the correction process based on the magnitude relation among the rendering input signal values of the sub-pixels  49  in the same pixel  48 . For example, when the BGR rendering process is performed, and the image display panel  40  has the first arrangement pattern and the first BW arrangement, the display device  10 A performs the correction process on the pixel  48   (a+3,b)  in which, among the first sub-pixel rendering input signal value x A1−(a+3,b) , the second sub-pixel rendering input signal value x A2−(a+3,b) , the third sub-pixel rendering input signal value x A3−(a+3,b) , the first sub-pixel rendering input signal value x A1−(a+3,b)  is smallest, and the third sub-pixel rendering input signal value x A3−(a+3,b)  is largest. Further, when the BGR rendering process is performed, and the image display panel  40  has the first arrangement pattern and the second BW arrangement, the display device  10 A performs the correction process on the pixel  48   (a+1,b)  in which, among the first sub-pixel rendering input signal value x A1−(ail,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , the third sub-pixel rendering input signal value x A3−(a+1,b) , the first sub-pixel rendering input signal value x A1−(a+1,b)  is largest and, the third sub-pixel rendering input signal value x A3−(a+1,b)  is smallest. The display device  10 A performs the correction process on only the pixel  48  satisfying the conditions, and does not perform the correction process on the other pixels  48 . However, when the rendering process to be performed is the BGR rendering process, the display device  10 A may perform the correction process on all the pixels  48  that have undergone the rendering process in the case of the first arrangement pattern. 
     As described above, the rendering processing unit  74 A may perform any one of the RGB rendering and the BGR rendering which is decided in advance. Thus, the rendering process of the rendering processing unit  74 A is a process of causing the rendering input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel (x A1−(a+1,b ), x A2−(a+1,b) , x A3−(a+1,b) ) in the pixel  48   (a+1,b)  to be values between the input signal values of the sub-pixels of the pixel  48   (a,b)  and the input signal values of the sub-pixels of the pixel  48   (a+2,b) . Further, the rendering process of the rendering processing unit  74 A is a process of causing the second sub-pixel rendering input signal value x A2−(a+1,b)  to be a value between the first sub-pixel rendering input signal value x A1−(a+1,b)  and the third sub-pixel rendering input signal value x A3−(a+1,b) . 
     The W output signal generating unit  84 A calculates the fourth sub-pixel output signal value X 4−(a+1,b)  of the pixel  48   (a+1,b)  based on the fourth sub-pixel generation signal value X A4−(a+1,b)  and the first sub-pixel input signal value x 1−(a+1,b)  the second sub-pixel input signal value x 2−(a+1,b) , or the third sub-pixel input signal value x 3−(a+1,b)  in the pixel  48   (a+1,b) . The W output signal generating unit  84 A performs the averaging process based on the input signal values of the same pixels and thus can suppress the deterioration of the image by appropriately increasing the luminance of the fourth sub-pixel  49 W of the pixel that has undergone the rendering process. 
     The W output signal generating unit  84 A may generate the output signal of the fourth sub-pixel  49 W of the pixel  48   (a+1,b)  based on the generation signal of the fourth sub-pixel  49 W of the pixel  48   (a+1,b)  and the output signal or the generation signal of the fourth sub-pixel of the pixel adjacent to the pixel  48   (a+1,b) . In this case, the W output signal generating unit  84 A preferably performs the averaging process of the generation signal of the fourth sub-pixel  49   (a+1,b)  of the pixel  48   (a+1,b)  and the output signal or the generation signal of the fourth sub-pixel of the pixel neighboring the pixel  48   (a+1,b)  using the same method (Equation (11) or the like) as the averaging process based on the input signal values of the same pixels described above. Even when the neighboring pixel undergoes the averaging process, the W output signal generating unit  84 A can suppress the deterioration of the image by appropriately increasing the luminance of the fourth sub-pixel  49 W of the pixel that has undergone the rendering process. In this case, the neighboring pixel of the pixel  48   (a+1,b)  is the pixel  48   (a+2,b)  that is adjacent in the first direction F 1 , but the pixel that is adjacent in the second direction F 2 , the third direction F 3 , or the fourth direction F 4  may be used as the neighboring pixel of the pixel  48   (a+1,b) . 
     The W output signal generating unit  84 A calculates the fourth sub-pixel output signal value X 4−(a+1,b)  of the pixel  48   (a+1,b)  by averaging the fourth sub-pixel generation signal value X A4−(a+1,b)  and the maximum value of the first sub-pixel rendering input signal value x A1−(a+1,b) , the second sub-pixel rendering input signal value x A2−(a+1,b) , and the third sub-pixel rendering input signal value x A3−(a+1,b)  of the pixel  48   (a+1,b) . The W output signal generating unit  84 A performs the averaging process based on the maximum rendering input signal value of the same pixel and thus can suppress the deterioration of the image by appropriately increasing the luminance of the fourth sub-pixel  49 W of the pixel that has undergone the rendering process. 
     Next, a relation between the display mode (the pattern information) and a pixel that undergoes the correction process in the image display panel according to the second embodiment will be described.  FIG. 24A  is a table indicating a relation between the display mode and a condition of a pixel that undergoes the correction process in the image display panel according to the second embodiment. As illustrated in  FIG. 24A , the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  is satisfied when the image display panel  40  is in the first portrait mode and has the second arrangement pattern and the first BW arrangement, and the RGB rendering is performed. Further, when the image display panel  40  is in the first landscape mode and has the first arrangement pattern and the second BW arrangement, and the BGR rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  is satisfied. When the image display panel  40  is in the second portrait mode and has the first arrangement pattern and the first BW arrangement, and the BGR rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  is satisfied. Further, when the image display panel  40  is in the second landscape mode and has the second arrangement pattern and the second BW arrangement, and the RGB rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A1−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  is satisfied. 
     An image display panel with which the display device  10 A is equipped is not limited to the image display panel  40  having the sub-pixel arrangement illustrated in  FIG. 24A . An image display panel with which the display device  10 A is equipped may differ in the sub-pixel arrangement from the image display panel  40  when the display mode is fixed as long as the first sub-pixel  49 R, the second sub-pixel  49 G, the third sub-pixel  49 B, the fourth sub-pixel  49 W are arranged in the pixel  48  in the 2×2 matrix form.  FIG. 24B  is a table indicating a relation between the display mode and a condition of a pixel that undergoes the correction process in another example of the image display panel according to the second embodiment.  FIG. 24B  illustrates a relation between the display mode and the pixel that undergoes the correction process in the image display panel  40 S illustrated in  FIG. 20B . 
     As illustrated in  FIG. 24B , when the image display panel  40 S is in the first portrait mode and has the first arrangement pattern and the second BW arrangement, and the BGR rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A1−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  is satisfied. When the image display panel  40 S is in the first landscape mode and has the second arrangement pattern and the first BW arrangement, and the RGB rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x (A3−(p,q)  is satisfied. When the image display panel  40 S is in the second portrait mode and has the second arrangement pattern and the second BW arrangement, and the RGB rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A−(p,q) &gt;x A2−(p,q) &gt;x A3−(p,q)  is satisfied. Further, when the image display panel  40 S is in the second landscape mode and has the first arrangement pattern and the first BW arrangement, and the BGR rendering is performed, the display device  10 A performs the correction process on the pixel  48   (p,q)  in which the relation of x A1−(p,q) &lt;x A2−(p,q) &lt;x A3−(p,q)  is satisfied. 
     The display device  10 A may include the image display panel  40 S described above, similarly to the first embodiment. Specifically, the display device  10 A may include the image display panel having a different sub-pixel arrangement from those of the image display panels  40  and  40 S as long as 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 are arranged in the pixel  48  in the 2×2 matrix form, similarly to the first embodiment. 
     Third Embodiment 
     Next, a third embodiment will be described. A display device  10 B according to the third embodiment (a third aspect) differs from that of the second embodiment in that the pattern information is not acquired, an output signal difference between the sub-pixel that has undergone the rendering process and the neighboring sub-pixel is detected, and the correction process is performed on the rendering input signal of the fourth sub-pixel based on the output signal difference. In a configuration of the display device  10 B according to the third embodiment, a description of portions common to those of the second embodiment will be omitted. 
     Configuration of Signal Processing Unit 
       FIG. 25  is a block diagram illustrating a configuration of the signal processing unit according to the third embodiment. As illustrated in  FIG. 25 , a signal processing unit  20 B according to the third embodiment includes a rendering unit  24 A, an α calculating unit  82 B, a sub-pixel generation signal unit  83 B, a correction process deciding unit  76 B, a W output signal generating unit  84 B, and an output signal generating unit  88 B. The signal processing unit  20 B does not include the pattern information acquiring unit and does not acquire the pattern information indicating the first arrangement pattern or the second arrangement pattern. 
     The rendering unit  24 A performs a predetermined rendering process (here, the RGB rendering), and generates the rendering input signal, similarly to the second embodiment. 
     The α calculating unit  82 B acquires the rendering input signal of the pixel  48  that has undergone the rendering process and the input signals of the other pixels from the rendering unit  24 A, and calculates the expansion coefficient α using the same method as that of the second embodiment. The α calculating unit  82 B outputs the input signals, the rendering input signals, and the information of the expansion coefficient α to the sub-pixel generation signal unit  83 B. 
     The sub-pixel generation signal unit  83 B generates generation signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel in all the pixels  48  in one frame based on the input signals, the rendering input signals, and the expansion coefficient α. The sub-pixel generation signal unit  83 B generates generation signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel for the pixel  48  that has undergone the rendering process based on the rendering input signals and the expansion coefficient α. Further, the sub-pixel generation signal unit  83 B generates generation signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel for the other pixels  48  based on the input signals and the expansion coefficient α. A process of generating the generation signal through the sub-pixel generation signal unit  83 B will be described later. 
     The correction process deciding unit  76 B acquires the generation signals of the sub-pixels in all the pixels  48  in one frame from the sub-pixel generation signal unit  83 B. The correction process deciding unit  76 B decides to generate the output signal of the fourth sub-pixel  49 W through the correction process for the pixel  48  that has undergone the rendering process based on the generation signals of the sub-pixels. The correction process deciding unit  76 B generates the correction decision information which includes the information indicating whether or not the correction process is performed. However, the correction process deciding unit  76 B may not acquire the generation signals of the sub-pixels in all the pixels  48  in one frame as long as the generation signal of the pixel  48  that has undergone the rendering process and the generation signal of the pixel neighboring the pixel  48  in the X direction are acquired. A method of deciding the correction process through the correction process deciding unit  76 B will be described later. 
     The W output signal generating unit  84 B generates the fourth sub-pixel output signal of the pixel  48  that is decided to perform the correction process based on the correction decision information and the generation signal. 
     The output signal generating unit  88 B generates and outputs the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel for the pixel  48  that has undergone the correction process based on the fourth sub-pixel output signal and the generation signal. The output signal generating unit  88 B outputs the generation signals as the output signal for the other pixels  48 . 
     Process Operation of Signal Processing Unit 
     Next, a process operation of the signal processing unit  20 B will be described. The rendering unit  24 A and the α calculating unit  82 B perform the rendering process and calculate the expansion coefficient α using the same method as that of the second embodiment. 
     When the rendering process is assumed to be performed on the pixel  48   (a+1,b) , the sub-pixel generation signal unit  83 B calculates the fourth sub-pixel generation signal value x A4−(a+1,b)  based on Equation (10) for the pixel  48   (a+1,b) . Further, the sub-pixel generation signal unit  83 B calculates the first sub-pixel generation signal value X A1−(a+1,b) , the second sub-pixel generation signal value X A2−(a+1,b) , and the third sub-pixel generation signal value X A2−(a+1,b)  based on Equations (12) to (14) for the pixel  48   (a+1,b) . The sub-pixel generation signal unit  83 B calculates the fourth sub-pixel generation signal value based on Equation (10) using the input signal value instead of the rendering input signal value for the pixel  48  that has not undergone the rendering process. Further, the sub-pixel generation signal unit  83 B calculates the generation signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel based on Equations (12) to (14) using the input signal value instead of the rendering input signal value for the pixel  48  that has not undergone the rendering process. In other words, the sub-pixel generation signal unit  83 B calculates the generation signal values of the sub-pixels for all the pixels  48  in one frame. 
     Next, a method of deciding the correction process through the correction process deciding unit  76 B will be described.  FIG. 26  is a schematic diagram illustrating an arrangement of the sub-pixels and the generation signal values.  FIG. 26  illustrates the generation signal values that are generated based on the rendering input signal values and the rendering input signals by the display device  10 B. As illustrated in  FIG. 26 , the rendering input signal values of the pixels  48  are the same as those in the second embodiment. Further, as illustrated in  FIG. 26 , the generation signal values of the pixels  48  according to the third embodiment are the same as, for example, the output signal values of the display device  10 Y according to the first comparative example described with reference to  FIG. 18 . 
     Here, a sub-pixel is referred to as a “neighboring sub-pixel” that neighbors the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process in the orthogonal direction (here, the Y direction) orthogonal to the processing direction and belongs to the same pixel  48 . Further, a plurality of sub-pixels  49  (four sub pixels  49 ) are referred to as “both-side sub-pixels” that neighbor the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process or the neighboring sub-pixel in the first direction F 1  or the second direction F 2 . The correction process deciding unit  76 B decides whether or not the output signal of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process is generated through the correction process, based on the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels. In further detail, the correction process deciding unit  76 B decides that the output signal of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process is generated through the correction process when the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the four both-side sub-pixels, and a difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the four both-side sub-pixels is a predetermined value or more. 
     Next, a method of deciding whether or not the correction process is performed on the pixel  48   (a+1,b)  that has undergone the rendering process will be described. Among the sub-pixels of the pixel  48   (a+1,b) , a sub-pixel neighboring the fourth sub-pixel  49 W (a+1,b)  in the orthogonal direction (here, the Y direction) is a first sub-pixel  49 R (a+1,b) . Thus, in this case, the first sub-pixel  49 R (a+1,b)  is the neighboring sub-pixel. Further, sub-pixels neighboring the fourth sub-pixel  49 W (a+1,b)  or the first sub-pixel  49 R (a+1,b)  in the processing direction (here, the first direction F 1 ) or an opposite direction (here, the second direction F 2 ) opposite to the processing direction are a second sub-pixel  49 G (a+1,b)  a third sub-pixel  49 B (a+1,b) , second sub-pixel  49 G (a+2,b) , and a third sub-pixel  49 B (a+2,b) . Thus, in this case, the second sub-pixel  49 G (a+1,b)  the third sub-pixel  49 B (a+1,b)  the second sub-pixel  49 G (a+2,b) , and the third sub-pixel  49 B (a+2,b)  are the both-side sub-pixels. The correction process deciding unit  76 B decides to perform the correction process on the fourth sub-pixel  49 W (a+1,b)  of the pixel  48   (a+1,b)  when the generation signal value of the first sub-pixel  49 R (a+1,b)  is smaller than the generation signal values of the second sub-pixel  49 G (a+1,b) , the third sub-pixel  49 B (a+1,b) , the second sub-pixel  49 G (a+2,b) , and the third sub-pixel  49 B (a+2,b) , and a difference between the generation signal values is a predetermined value or more. Here, the generation signal value of the first sub-pixel  49 R (a+1,b)  serving as the neighboring sub-pixel is larger than the generation signal values of the both-side sub-pixels. Thus, the correction process deciding unit  76 B decides not to perform the correction process on the pixel  48   (a+1,b) . 
     Next, a method of deciding whether or not the correction process is performed on the pixel  48   (a+3,b)  that has undergone the rendering process will be described. Among the sub-pixels of the pixel  48   (a+3,b) , a sub-pixel neighboring the fourth sub-pixel  49 W (a+3,b)  in the orthogonal direction (here, the Y direction) is a first sub-pixel  49 R (a+3,b) . Thus, in this case, the first sub-pixel  49 R (a+3,b)  is the neighboring sub-pixel. Further, sub-pixels neighboring the fourth sub-pixel  49 W (a+3,b)  or the first sub-pixel  49 R (a+3,b)  in the processing direction (here, the first direction F 1 ) or the opposite direction (here, the second direction F 2 ) are a second sub-pixel  49 G (a+3,b) , a third sub-pixel  49 B (a+3,b) , a second sub-pixel  49 G (a+4,b)  and a third sub-pixel  49 B (a+4,b)  Thus, in this case, the second sub-pixel  49 G (a+3,b) , the third sub-pixel  49 B (a+3,b) , the second sub-pixel  49 G (a+4,b)  and the third sub-pixel  49 B (a+4,b)  are the both-side sub-pixels. The correction process deciding unit  76 B decides to perform the correction process on the fourth sub-pixel  49 W (a+3,b)  of the pixel  48   (a+3,b)  when the generation signal value of the first sub-pixel  49 R (a+3,b)  is smaller than the generation signal values of the second sub-pixel  49 G (a+3,b) , the third sub-pixel  49 B (a+3,b) , the second sub-pixel  49 G (a+4,b)  and the third sub-pixel  49 B (a+4,b) , and the difference between the generation signal values is a predetermined value or more. Here, for example, the predetermined value is set to 50. In this case, the generation signal value of the first sub-pixel  49 R (a+3,b)  serving as the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, and the difference between the values is 50 serving as the predetermined value or more. Thus, the correction process deciding unit  76 B decides to perform the correction process on the pixel  48   (a+3,b) . 
     The W output signal generating unit  84 B generates the fourth sub-pixel output signal of the pixel  48  that is decided to perform the correction process using the same method as that of the W output signal generating unit  84 A according to the second embodiment. The W output signal generating unit  84 B calculates the fourth sub-pixel output signal value of the pixel  48  that is decided to perform the correction process by performing the averaging process, that is, the correction process based on Equation (11). 
     For the pixel  48  that has undergone the correction process, the output signal generating unit  88 B generates the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48  that has undergone the correction process using the same method as that of the output signal generating unit  88 A according to the second embodiment. The output signal generating unit  88 B has not performed the correction process on the other pixels  48  and thus outputs the generation signals of the sub-pixels calculated by the sub-pixel generation signal unit  83 B to the image display panel driving unit  30  as the output signal. 
     Next, a process of the process operation of the signal processing unit  20 B will be described based on a flowchart.  FIG. 27  is a flowchart for describing a process operation of the signal processing unit according to the third embodiment. As illustrated in  FIG. 27 , first, the rendering position deciding unit  21  of the signal processing unit  20 B selects the pixel  48  that undergoes the rendering process based on the input signal (step S 52 ). After the pixel  48  that undergoes the rendering process is selected, the rendering processing unit  74 A performs the rendering process on the selected pixel  48 , and generates the rendering input signal (step S 54 ). In the third embodiment, the rendering process is the RGB rendering. 
     After the rendering input signal is generated in step S 54 , the sub-pixel generation signal unit  83 B generates the generation signals of the sub-pixels  49  of the pixel  48  that has undergone the rendering process based on the rendering input signal (step S 56 ). The sub-pixel generation signal unit  83 B calculates the fourth sub-pixel generation signal value X A4−(a+1,b)  based on Equation (11) for the pixel  48   (a+1,b)  that has undergone the rendering process. 
     The sub-pixel generation signal unit  83 B calculates the first sub-pixel generation signal value X A1−(a+1,b) , the second sub-pixel generation signal value X A2−(a+1,b) , and the third sub-pixel generation signal value X A3−(a+1,b)  based on Equations (12) to (14) for the pixel  48   (a+1,b) . 
     After the generation signals of the sub-pixels  49  of the pixel  48  that has undergone the rendering process are generated, the correction process deciding unit  76 B determines whether or not the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, and the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is a predetermined value or more (step S 58 ). 
     When the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, and the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is the predetermined value or more (Yes in step S 58 ), the correction process deciding unit  76 B decides to perform the correction process on the pixel  48  that has undergone the rendering process, and the W output signal generating unit  84 B generates the fourth sub-pixel output signal through the correction process for the pixel  48  decided to perform the correction process (step S 60 ). The W output signal generating unit  84 B performs the correction process based on Equation (11), and generates the fourth sub-pixel output signal of the pixel  48  decided to perform the correction process. 
     After the fourth sub-pixel output signal of the pixel  48  decided to perform the correction process is generated through the correction process, the output signal generating unit  88 B generates the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48  that has undergone the correction process (step S 62 ). The output signal generating unit  88 B generates the output signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the pixel  48  that has undergone the correction process using the same method as that of the output signal generating unit  88 A according to the second embodiment. 
     When the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, and the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is not the predetermined value or more (No in step S 58 ), the correction process deciding unit  76 B decides not to perform the correction process on the pixel  48  that has undergone the rendering process, and the output signal generating unit  88 B outputs the generation signals of the sub-pixels generated in step S 56  as the output signal (step S 64 ). When the generation signal value of the neighboring sub-pixel is larger than the generation signal values of the both-side sub-pixels, the correction process deciding unit  76 B decides not to perform the correction process. Further, even when the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, but the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is not the predetermined value or more, the correction process deciding unit  76 B decides not to perform the correction process. After step S 62  or step S 64  is performed, the current process ends. 
     Display Example 
     Next, a display example of the sub-pixels when the rendering process and the correction process according to the third embodiment are performed will be described. As described above with reference to  FIG. 18 , the display device  10 Y according to the first comparative example does not perform the correction process described in the third embodiment, and thus the line L 1  of  FIG. 18  is likely to be recognized as the dark line when the rendering process is performed. 
       FIG. 28  is a schematic diagram illustrating the output signals of the sub-pixels when the rendering process and the correction process according to the third embodiment are performed.  FIG. 28  illustrates the generation signal values which are generated based on the input signal and the rendering input signal and the output signal values which are generated based on the generation signal values by the display device  10 B. The rendering input signal values and the generation signal values of the pixels illustrated in  FIG. 28  are the same as those of  FIG. 26 . 
     The generation signal values illustrated in  FIG. 28  are provisional signal values calculated based on the rendering input signal value before the correction process is performed and have the same values as the output signal values according to the first comparative example. Thus, when the generation signal is output as the output signal without change, as illustrated in  FIG. 28 , a line L 5  formed by the first sub-pixel  49 R (a+3,b)  and the fourth sub-pixel  49 W (a+3,b ) in the pixel  48   (a+3,b)  is likely to be recognized as the dark line, similarly to the line L 1  of  FIG. 18 . However, the display device  10 B according to the third embodiment performs the correction process on the pixel  48   (a+3,b)  since the generation signal value of the neighboring sub-pixel of the pixel  48   (a+3,b)  is smaller than the generation signal values of the both-side sub-pixels, and the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is the predetermined value or more as described above. 
     As illustrated in  FIG. 28 , in the pixel  48   (a+3,b) , that is, the pixel  48   (a+3,b)  that has undergone the correction process, the output signal value X 1−(a+3,b)  of the first sub-pixel is 43, the output signal value X 2−(a+3,b)  of the second sub-pixel is 115, the output signal value X 3−(a+3,b)  of the third sub-pixel is 188, and the output signal value X 4−(a+3,b)  of the fourth sub-pixel is 175. In the pixel  48   (a+3,b) , the output signal value X 4−(a+3,b)  of the fourth sub-pixel is increased to be larger than the generation signal value through correction process. The display device  10 B according to the third embodiment can increase the luminance of a line L 6  along the Y direction in which the sub-pixel  49 R and the sub-pixel  49 W of the pixel  48   (a+3,b)  are arranged by increasing the output value of the sub-pixel  49 W of the pixel  48   (a+3,b)  that is large in the difference of the output signal value with the both-side sub-pixels. Thus, the display device  10 B can suppress, for example, the black line from being recognized and suppress the deterioration of the image. In addition, the display device  10 B does not perform the correction process on the pixel  48   (a+1,b)  in which the difference of the output signal value with the both-side sub-pixels is small, and the black line is unlikely to be recognized. Thus, the display device  10 B can suppress the deterioration of the image such as recognition of the black line and can smoothly display the image by appropriately performing the rendering process. 
     As described above, the display device  10 B according to the third embodiment includes the image display panel  40  in which a plurality of pixels  48  each of which includes 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 arranged in a 2×2 matrix form are arranged on the display region  43  of the square shape having the first side (the short side  41 ) and the second side (the long side  42 ) in the matrix form. The image display panel  40  receives the image information corresponding to the portrait mode in which the direction along the first side is a predetermined one direction (here, the X direction) of the display image or the landscape mode in which the direction along the second side is a predetermined one direction (here, the X direction) of the display image. The signal processing unit  20 B according to the third embodiment further includes the rendering unit  24 A that performs the rendering process on the pixel  48   (a+1,b)  when the difference between the input signal values of the sub-pixel  49   (a,b)  of the pixel  48   (a,b)  and the input signal values of the sub-pixels  49   (a+2,b)  of the pixel  48   (a+2,b)  is a predetermined threshold value or more. The signal processing unit  20 B further includes the sub-pixel generation signal unit  83 B that generates the generation signals 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 based on the input signal values and the rendering input signal values of the sub-pixels  49  in each pixel  48 . The signal processing unit  20 B further includes the correction process deciding unit  76 B that decides whether or not the output signal of the fourth sub-pixel  49 W (a+1,b)  is generated through the correction process based on the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels. The neighboring sub-pixel is served as the sub-pixel of the pixel  48   (a+1,b)  neighboring the fourth sub-pixel  49 W (a+1,b)  of the pixel  48   (a+1,b)  in the orthogonal direction (here, the Y direction). The both-side sub-pixels are served as a plurality of sub-pixels  49  neighboring the fourth sub-pixel  49 W (a+1,b)  or the neighboring sub-pixel in the processing direction (here, the first direction F 1 ) or the opposite direction (here, the second direction F 2 ). The signal processing unit  20 B performs the correction process based on the decision of the correction process deciding unit  76 B, by performing the correction process by performing the averaging process, based on the generation signal of the fourth sub-pixel  49 W (a+1,b)  and the input signals of the other sub-pixels, and generates the output signal of the fourth sub-pixel  49 W (a+1,b) . 
     The display device  10 B decides whether or not the correction process is performed on the pixel  48  that has undergone the rendering process based on the output signal value of the neighboring sub-pixel in the same column as the sub-pixel  49 W and the output signal values of the both-side sub-pixels adjacent to both sides thereof. Thus, the display device  10 B can suppress, for example, the recognition of the black line and suppress the deterioration of the image when the dark line is likely to be recognized by, for example, the output signal difference between the neighboring sub-pixel and the both-side sub-pixels caused by the rendering process. 
     The correction process deciding unit  76 B decides to generate the output signal of the fourth sub-pixel  49 W of the pixel  48  that has undergone the rendering process through the correction process when the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the four both-side sub-pixels, and the difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the four both-side sub-pixels is a predetermined value or more. For the pixel  48  that has undergone the rendering process, the display device  10 B increases luminance of a column in which the sub-pixel  49 W is positioned by increasing the output value of the sub-pixel  49 W when the difference between the output signal value of the sub-pixel in the same column as the sub-pixel  49 W and the output signal value of the sub-pixel adjacent to both sides thereof is large. Thus, the display device  10 B can suppress, for example, the recognition of the dark line and suppress the deterioration of the image. 
     The W output signal generating unit  84 B performs the same averaging process as that of the W output signal generating unit  84 A according to the second embodiment as described above. Thus, the W output signal generating unit  84 B may generate the output signal of the fourth sub-pixel  49   (a+1,b)  of the pixel  48   (a+1,b)  based on the generation signal of the fourth sub-pixel  49   (a+1,b)  of the pixel  48   (a+1,b)  and the output signal or the generation signal of the fourth sub-pixel of the pixel neighboring the pixel  48   (a+1,b)  using the same method as that of the W output signal generating unit  84 A according to the second embodiment. 
     Modification 
     Next, a modification of the first embodiment will be described. A display device  10 D according to the modification differs from that of the first embodiment in that one pixel includes three sub-pixels. In the display device  10 D according to the modification, a description of portions common to those of the first embodiment will be omitted. 
       FIG. 29  is a schematic diagram illustrating an example of an arrangement of the sub-pixels in the portrait mode according to the modification.  FIG. 30  is a schematic diagram illustrating an example of an arrangement of the sub-pixels in the landscape mode according to the modification.  FIG. 29  illustrates the first portrait mode in which the short side  41  is positioned at the side of the image in the third direction F 3 .  FIG. 30  illustrates the first landscape mode in which the short side  41  is positioned at the side of the image in the first direction F 1 . 
     As illustrated in  FIGS. 29 and 30 , in an image display panel  40 D, a pixel  48 D A  serving as a first thinned pixel including a first sub-pixel  49 DR, a second sub-pixel  49 DG, and a third sub-pixel  49 DB and a pixel  48 D B  serving as a second thinned pixel including a first sub-pixel  49 DR, a second sub-pixel  49 DG, and a fourth sub-pixel  49 DW are alternately arranged in the X direction and the Y direction. However, an arrangement of the pixel  48 D A  and the pixel  48 D B  is not limited thereto. For example, the pixel  48 D A  and the pixel  48 D B  are alternately arranged in the X direction, but the pixel  48 D A  may be consecutively arranged in the Y direction, and the pixel  48 D B  may be consecutively arranged in the Y direction. Alternatively, the pixel  48 D A  and the pixel  48 D B  are alternately arranged in the Y direction, but the pixel  48 D A  may be consecutively arranged in the X direction, and the pixel  48 D B  may be consecutively arranged in the X direction. In both of the arrangements of the pixel  48 D A  and the pixel  48 D B , in the two pixels in the X direction and the two pixels in the Y direction, the number of third sub-pixels  49 DB is equal to the number of fourth sub-pixels  49 DW, and a color balance is kept even though the third color is replaced with the fourth color. In any other pixel arrangement, a color balance is kept even though the third color is replaced with the fourth color as long as the arrangement of the pixel  48 D A  and the pixel  48 D B  is an arrangement in which in the four pixels in the X direction and the four pixels in the Y direction, the number of third sub-pixels  49 DB is equal to the number of fourth sub-pixels  49 DW. 
     As illustrated in  FIG. 29 , in the pixel  48 D A , in the first portrait mode, the second sub-pixel  49 DG and the first sub-pixel  49 DR are arranged in the first row along the X direction, the first sub-pixel  49 DR neighbors the second sub-pixel  49 DG at the side of the second sub-pixel  49 DG in the first direction F 1 . Further, in the pixel  48 D A , in the first portrait mode, the third sub-pixel  49 DB is arranged in the second row adjacent to the first row in the third direction F 3 , the third sub-pixel  49 DB neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in the third direction F 3 . Furthermore, in the pixel  48 D B , in the first portrait mode, the second sub-pixel  49 DG and the first sub-pixel  49 DR are arranged in the first row along the X direction, the first sub-pixel  49 DR neighbors the second sub-pixel  49 DG at the side of the second sub-pixel  49 DG in the first direction F 1 . Moreover, in the pixel  48 D B , in the first portrait mode, the fourth sub-pixel  49 DW is arranged in the second row adjacent to the first row in the third direction F 3 , the fourth sub-pixel  49 DW neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in the third direction F 3 . 
     As illustrated in  FIG. 30 , in the pixel  48 D A , in the first landscape mode, the first sub-pixel  49 DR and the second sub-pixel  49 DG are arranged in the first column along the Y direction, the second sub-pixel  49 DG neighbors the first sub-pixel  49 DR at the side of the first sub-pixel  49 DR in the third direction F 3 . Further, in the pixel  48 D A , in the first landscape mode, the third sub-pixel  49 DB neighboring the side of the second sub-pixel  49 DG in the first direction F 1  is arranged in the second column adjacent to the first column in the first direction F 1 , the third sub-pixel  49 DB neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in the first direction F 1 . a In the pixel  48 D B , in the first landscape mode, the first sub-pixel  49 DR and the second sub-pixel  49 DG are arranged in the first column along the Y direction, the second sub-pixel  49 DG neighbors the first sub-pixel  49 DR at the side of the first sub-pixel  49 DR in the third direction F 3 . Furthermore, in the pixel  48 D B , in the first landscape mode, the fourth sub-pixel  49 DW is arranged in the second column adjacent to the first column in the first direction F 1 , the fourth sub-pixel  49 DW neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in the first direction F 1 . 
     As described above, the sub-pixel arrangement in the X direction and the Y direction according to the modification changes according to the display mode. In the pixel  48 D A  and the pixel  48 D B  according to the modification, sub-pixels  49 D are arranged as follows regardless of the display mode. In other words, in the pixel  48 D A  serving as the first pixel, the first sub-pixel  49 DR and the second sub-pixel  49 DG are arranged in a first arrangement along a predetermined direction to be adjacent to each other in the predetermined direction. The third sub-pixel  49 DB neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in an intersection direction serving as a direction intersecting with the predetermined direction is arranged in a second arrangement neighboring the first arrangement in the intersection direction. Further, in the pixel  48 D B  serving as the second pixel, the first sub-pixel  49 DR and the second sub-pixel  49 DG are arranged in a first arrangement along a predetermined direction to be adjacent to each other in the predetermined direction. The fourth sub-pixel  49 DW neighbors the first sub-pixel  49 DR and the second sub-pixel  49 DG in the intersection direction is arranged in a second arrangement neighboring the first arrangement in the intersection direction. 
     In the modification, the arrangement of the sub-pixels  49  in the first arrangement pattern is an arrangement in which the second sub-pixel  49 DG or the third sub-pixel  49 DB belonging to the same pixel  48  neighbors the side of the first sub-pixel  49 DR in the processing direction (here, the first direction F 1 ) or an arrangement in which the third sub-pixel  49 DB belonging to the same pixel  48  neighbors the side of the second sub-pixel  49 DG in the processing direction (here, the first direction F 1 ). Further, in the modification, the arrangement of the sub-pixels  49  in the second arrangement pattern is an arrangement in which the first sub-pixel  49 DR belonging to the same pixel  48  neighbors the side of the second sub-pixel  49 DG in the processing direction (here, the first direction F 1 ) or an arrangement in which the second sub-pixel  49 DG or the first sub-pixel  49 DR belonging to the same pixel  48  neighbors the side of the third sub-pixel  49 DB in the processing direction (here, the first direction F 1 ). Thus, in the modification, the first landscape mode and the second portrait mode have the first arrangement pattern, and the first portrait mode and the second landscape mode have the second arrangement pattern. The relation between the first and second arrangement patterns and the display mode differs according to a design of the sub-pixel arrangement and is not limited to the relation of the modification. 
     A process of the signal processing unit  20  according to the modification is the same as that of the signal processing unit  20  according to the first embodiment. However, in the signal processing unit  20  according to the modification, the output signal generating unit  88  may generate a corrected output signal of the fourth sub-pixel  49 DW of the pixel  48 D A  by performing the averaging process using the output signal of the fourth sub-pixel  49 DW of the pixel  48 D A  and the output signal of the fourth sub-pixel  49 DW of the pixel  48 D B  neighboring the pixel  48 D A  in the orthogonal direction (here, the Y direction) orthogonal to the processing direction. In this case, the output signal generating unit  88  outputs the corrected output signal to the image display panel driving unit  30  as the output signal of the fourth sub-pixel  49 DW of the pixel  48 D A . Further, the output signal generating unit  88  may generate a corrected output signal of the third sub-pixel  49 DB of the pixel  48 D B  by performing the averaging process using the output signal of the third sub-pixel  49 DB of the pixel  48 D B  and the output signal of the third sub-pixel  49 DB of the pixel  48 D A  neighboring the pixel  48 D B  in the orthogonal direction (here, the Y direction) orthogonal to the processing direction. In this case, the output signal generating unit  88  outputs the corrected output signal to the image display panel driving unit  30  as the output signal of the third sub-pixel  49 DB of the pixel  48 D B . 
     Next, a display example of the sub-pixels when the rendering process is performed in the display device  10 D according to the modification will be described.  FIG. 31  is a schematic diagram illustrating the output signals of the sub-pixels when a rendering process according to a second comparative example is performed. A display device  10 Z A  according to the second comparative example has the same sub-pixel arrangement as the display device  10 D according to the modification and can perform switching of the display mode (the landscape mode and the portrait mode). As illustrated in  FIG. 31 , an image display panel  40 Z A  according to the second comparative example includes a pixel  48 Z A(a,b) , a pixel  48 Z A(a+1,b) , a pixel  48 Z A(a+2,b) , a pixel  48 Z A(a+3,b) , and a pixel  48 Z A(a+4,b)  which are arranged in the first direction F 1 .  FIG. 31  illustrates the sub-pixel arrangement in the first portrait mode. 
     The display device  10 Z A  according to the second comparative example performs the RGB rendering in all the display modes. In the example of  FIG. 31 , the display device  10 Z A  according to the second comparative example performs the RGB rendering in the first portrait mode, and generates the same rendering input signals as those of  FIG. 13 . As illustrated in  FIG. 31 , output signal values of a first sub-pixel  49 Z A R, a second sub-pixel  49 Z A G, and a fourth sub-pixel  49 Z A W of the pixel  48 Z A(a,b)  according to the second comparative example are 180. In the pixel  48 Z A(a+1,b) , an output signal value of the first sub-pixel  49 Z A R is 230, an output signal value of the second sub-pixel  49 Z A G is 180, and an output signal value of a third sub-pixel  49 Z A B is 110. Output signals of output signal values of the first sub-pixel  49 Z A R, the second sub-pixel  49 Z A G, and the fourth sub-pixel  49 Z A W of the pixel  48 Z A(a+2,b)  are 70. Further, in the pixel  48 Z A+3,b) , an output signal value of the first sub-pixel  49 Z A R is 110, an output signal value of the second sub-pixel  49 Z A G is 180, and an output signal value of the third sub-pixel  49 Z A B is 230. In the pixel  48 Z A(a+4,b) , output signal values of the first sub-pixel  49 Z A R, the second sub-pixel  49 Z A G, and the fourth sub-pixel  49 Z A W are 180. 
       FIG. 32  is a schematic diagram illustrating the output signals of the sub-pixels when a rendering process according to a modification is performed.  FIG. 32  illustrates an example in which, in the same first portrait mode as in  FIG. 31 , the rendering process according to the modification is performed, and the output signals are displayed. As described above, in the first portrait mode, the signal processing unit  20  according to the modification performs the BGR rendering. As illustrated in  FIG. 32 , output signals of sub-pixels of a pixel  48 D (a,b) , a pixel  48 D (a+2,b) , and a pixel  48 D (a+4,b)  have the same values as those of the second comparative example illustrated in  FIG. 31 . In the pixel  48 D (a+1,b) , an output signal value of the first sub-pixel  49 DR is 110, an output signal value of the second sub-pixel  49 DG is 180, and an output signal value of the third sub-pixel  49 DB is 230. Further, in the pixel  48 D (a+3,b) , an output signal value of the first sub-pixel  49 DR is 230, an output signal value of the second sub-pixel  49 DG is 180, and an output signal value of the third sub-pixel  49 DB is 110. 
     In the pixel  48 Z A(a+3,b)  according to the second comparative example, the output signal value of the third sub-pixel  49 Z A B is larger than the output signal values of the fourth sub-pixel  49 Z A W of the pixel  48 Z A(a+2,b)  adjacent thereto in the second direction F 2  and the fourth sub-pixel  49 Z A W of the pixel  48 Z A(a+4,b)  adjacent thereto in the first direction F 1 . On the other hand, the output signal value of the third sub-pixel  49 DB of the pixel  48 D (a+3,b)  according to the modification is larger than the fourth sub-pixel  49 DW of the pixel  48 D (a+2,b)  adjacent thereto in the second direction F 2  and smaller than the output signal value of the fourth sub-pixel  49 DW of the pixel  48 D (a+4,b)  adjacent thereto in the first direction F 1 . Thus, the display device  10 D according to the modification can change the output signals of the sub-pixels in the first direction F 1  more appropriately than the display device  10 Z A  according to the second comparative example and thus can smoothly display an image and improve visibility. Generally, the first sub-pixel  49 DR of the first color is higher in recognized luminance than the third sub-pixel  49 DB of the third color even when the output signal value of the first sub-pixel  49 DR of the first color is increased by the same value as the third sub-pixel  49 DB of the third color. In the display device  10 D according to the modification, since the output signal of the first sub-pixel  49 DR is larger than that of the third sub-pixel  49 DB in the pixel  48 D (a+3,b) , the luminance of the pixel  48 D (a+3,b)  is increased, and a display can be more smoothly performed. 
     Next, a display example in the first landscape mode will be described.  FIG. 33  is a schematic diagram illustrating the output signals of the sub-pixels when a rendering process according to a third comparative example is performed.  FIG. 33  illustrates the output signals in the first landscape mode in a display device  10 Z B  according to the third comparative example. 
     The display device  10 Z B  according to the third comparative example performs the BGR rendering in all the display modes. In the example of  FIG. 33 , the display device  10 Z B  according to the third comparative example performs the BGR rendering in the first landscape mode, and generates the same rendering input signals as those of  FIG. 14 . As illustrated in  FIG. 33 , output signals of sub-pixels of a pixel  48 Z B (a,b) , a pixel  48 Z B(a+2,b) , and a pixel  48 Z B(a+4,b)  have the same values as those of the second comparative example illustrated in  FIG. 31 . In the pixel  48 Z B(a+1,b) , an output signal value of the first sub-pixel  49 Z B R is 110, an output signal value of the second sub-pixel  49 Z B G is 180, and an output signal value of a third sub-pixel  49 Z B B is 230. Further, in the pixel  48 Z B(a+3,b) , an output signal value of the first sub-pixel  49 Z B R is 230, an output signal value of the second sub-pixel  49 Z B G is 180, and an output signal value of the third sub-pixel  49 Z B B is 110. The third sub-pixel  49 Z B B of the pixel  48 Z B(a+3,b)  is smaller in the output signal value than the sub-pixels adjacent to both sides in the X direction. For this reason, in the image display panel  40 Z B  according to the third comparative example, a line L 7  in which the third sub-pixel  49 Z B B of the pixel  48 Z B(a+3,b)  is arranged is darker than a portion therearound, recognized as a bark portion by the observer, and thus the deterioration of the image is likely to be recognized. 
       FIG. 34  is a schematic diagram illustrating the output signals of the sub-pixels when a rendering process according to a modification is performed.  FIG. 34  illustrates an example in which, in the same first landscape mode as in  FIG. 33 , the rendering process according to the modification is performed, and the output signals are displayed. As described above, in the first landscape mode, the signal processing unit  20  according to the modification performs the RGB rendering. As illustrated in  FIG. 34 , output signals of sub-pixels of a pixel  48 D (a,b) , a pixel  48 D (a+2,b)  and a pixel  48 D (a+4,b)  have the same values as those of the second comparative example illustrated in  FIG. 31 . On the other hand, in the pixel  48 D (a+1,b) , an output signal value of the first sub-pixel  49 DR is 230, an output signal value of the second sub-pixel  49 DG is 180, and an output signal value of the third sub-pixel  49 DB is 110. Further, in the pixel  48 D (a+3,b) , an output signal value of the first sub-pixel  49 DR is 110, an output signal value of the second sub-pixel  49 DG is 180, and an output signal value of the third sub-pixel  49 DB is 230. The third sub-pixel  49 DB of the pixel  48 D (a+3,b)  is suppressed from being smaller in the output signal value than the sub-pixels adjacent to both sides in the X direction. For this reason, in the image display panel  40 D according to the modification, since a line L 8  in which the third sub-pixel  49 DB of the pixel  48 D (a+3,b)  is arranged is suppressed from being darker than a portion therearound, and thus the deterioration of the image is suppressed. 
     As described above, the display device  10 D according to the modification includes the image display panel in which a plurality of first thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the third sub-pixel and a plurality of second thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the fourth sub-pixel are arranged in the display region of the square shape having the first side and the second side intersecting with the first side in the matrix form. In the first thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along a predetermined direction to be adjacent to each other in the predetermined direction, and the third sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction serving as the direction intersecting the predetermined direction. In the second thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along the predetermined direction to be adjacent to each other in the predetermined direction, and the fourth sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction. The image display panel receives the image information of the portrait mode in which a direction along the first side is a predetermined one direction of the display image or the landscape mode in which a direction along the second side is the one direction of the display image. The display device  10 D further includes the signal processing unit that generates the output signals from the input values of the input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel. The signal processing unit includes the rendering position deciding unit that decides whether or not the sub-pixel rendering process of changing the input signal values of the sub-pixels is performed when, in the first pixel, the second pixel neighboring the first pixel at the side in the predetermined processing direction, and the third pixel neighboring the second pixel at the side in the processing direction among the first thinned pixel and the second thinned pixel, the difference between the input signal values of the sub-pixels of the first pixel and the input signal values of the sub-pixels of the third pixel is a predetermined threshold value or more. The signal processing unit further includes the pattern information acquiring unit that acquires an arrangement of the sub-pixels in the processing direction of a display mode indicating either of the portrait mode and the landscape mode as pattern information indicating any one of a first arrangement pattern and a second arrangement pattern that differ in the arrangement of the sub-pixels. The signal processing unit further includes the rendering unit that generates rendering input signals of the sub-pixels of the second pixel by performing either of a first sub-pixel rendering process and a second sub-pixel rendering process of the sub-pixel rendering process which differ in a change in signal values of the input signals of the sub-pixels on input signals of the sub-pixels of the second pixel based on the decision of the rendering position deciding unit and the pattern information. Here, the processing direction is a direction along the first side of the image display panel when the display mode is the portrait mode and a direction along the second side of the image display panel when the display mode is the landscape mode. 
     Further, in the display device  10 D, preferably, the first sub-pixel rendering process is a process of causing an input signal value of the first sub-pixel in the second pixel to be a signal value between a first pixel input signal value and a third pixel input signal value, causing an input signal value of the second sub-pixel in the second pixel to be a value between the input signal value of the first sub-pixel in the second pixel and the third pixel input signal value, and causing an input signal value of the third sub-pixel in the second pixel to be a value between the input signal value of the second sub-pixel in the second pixel and the third pixel input signal value, and the second sub-pixel rendering process is a process of causing the input signal value of the first sub-pixel in the second pixel to be a signal value between the first pixel input signal value and the third pixel input signal value, causing the input signal value of the second sub-pixel in the second pixel to be a value between the input signal value of the first sub-pixel in the second pixel and the first pixel input signal value, and causing the input signal value of the third sub-pixel in the second pixel to be a value between the input signal value of the second sub-pixel in the second pixel and the first pixel input signal value. 
     Further, in the display device  10 D, preferably, when the pattern information indicates the first arrangement pattern, the second sub-pixel of the second pixel neighbors a side of the first sub-pixel of the second pixel in the processing direction, or the third sub-pixel of the second pixel neighbors a side of the second sub-pixel of the second pixel in the processing direction, when the pattern information indicates the second arrangement pattern, the first sub-pixel of the second pixel neighbors a side of the second sub-pixel of the second pixel in the processing direction, or the second sub-pixel of the second pixel neighbors a side of the third sub-pixel of the second pixel in the processing direction, and the rendering unit decides to perform the first sub-pixel rendering process when the pattern information indicates the first arrangement pattern, and decides to perform the second sub-pixel rendering process when the pattern information indicates the second arrangement pattern. 
     Further, in the display device  10 D, preferably, when the first pixel input signal value is larger than the third pixel input signal value, the first sub-pixel rendering process is a process of causing the input signal value of the first sub-pixel to be largest and causing the input signal value of the third sub-pixel to be smallest among the input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel, and the second sub-pixel rendering process is a process of causing the input signal value of the third sub-pixel to be largest and causing the input signal value of the first sub-pixel to be smallest among the input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the signal processing unit includes an output processing unit that generates the output signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel of the second pixel based on the rendering input signal, and the output processing unit decides an expansion coefficient related to the image display panel, obtains the output signal of the fourth sub-pixel of the second pixel based on the rendering input signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel and the expansion coefficient, obtains the output signal of the first sub-pixel of the second pixel based on the rendering input signal of the first sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, obtains the output signal of the second sub-pixel of the second pixel based on the rendering input signal of the second sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and obtains the output signal of the third sub-pixel of the second pixel based on the rendering input signal of the third sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient. 
     Further, the pixel arrangement of the display device  10 D according to the modification can be applied to the second embodiment. The display device  10 D according to the modification includes the image display panel in which a plurality of first thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the third sub-pixel and a plurality of second thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the fourth sub-pixel are arranged in the display region of the square shape having the first side and the second side intersecting with the first side in the matrix form. In the first thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along a predetermined direction to be adjacent to each other in the predetermined direction, and the third sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction serving as the direction intersecting the predetermined direction. In the second thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along the predetermined direction to be adjacent to each other in the predetermined direction, and the fourth sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction. The image display panel receives the image information of the portrait mode in which a direction along the first side is a predetermined one direction of the display image or the landscape mode in which a direction along the second side is the one direction of the display image. The display device  10 D further includes the signal processing unit that generates the output signals from the input values of the input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel. The signal processing unit includes the rendering unit that generates the rendering input signal by performing a predetermined sub-pixel rendering process of changing the signal values of the input signals of the sub-pixels of the second pixel when, in the first pixel, the second pixel neighboring the first pixel at a side in a predetermined processing direction, and the third pixel neighboring the second pixel at the side in the processing direction among the plurality of arranged pixels, the difference between the input signal values of the sub-pixels of the first pixel and the input signal values of the sub-pixels of the third pixel is a predetermined threshold value or more. The signal processing unit further includes the pattern information acquiring unit that acquires an arrangement of the sub-pixels in the processing direction of a display mode indicating either of the portrait mode and the landscape mode as pattern information indicating any one of a first arrangement pattern and a second arrangement pattern that differ in the arrangement of the sub-pixels. The signal processing unit further includes the correction process deciding unit that decides whether or not an output signal of the fourth sub-pixel of the second pixel is generated based on the pattern information through a correction process and a fourth sub-pixel generation signal unit that obtains a generation signal of the fourth sub-pixel of the second pixel based on the rendering input signals of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel, and an expansion coefficient related to the image display panel, based on the decision of the correction process deciding unit. The signal processing unit further includes the fourth sub-pixel output signal generating unit that performs the correction process by performing an averaging process based on the generation signal of the fourth sub-pixel of the second pixel and input signals of other sub-pixels, and generates the output signal of the fourth sub-pixel of the second pixel. The signal processing unit further includes the output signal generating unit that obtains the output signal of the first sub-pixel of the second pixel based on the rendering input signal of the first sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, obtains the output signal of the second sub-pixel of the second pixel based on the rendering input signal of the second sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and obtains the output signal of the third sub-pixel of the second pixel based on the rendering input signal of the third sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient. Here, the processing direction is a direction along the first side of the image display panel when the display mode is the portrait mode and a direction along the second side of the image display panel when the display mode is the landscape mode. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel to be a value between the first pixel input signal value and the third pixel input signal value and causing the input signal value of the second sub-pixel of the second pixel to be a value between the input signal value of the first sub-pixel of the second pixel and the input signal value of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal value of the second sub-pixel of the second pixel to be a value between the input signal value of the first sub-pixel of the second pixel and the third pixel input signal value and causing the input signal value of the third sub-pixel of the second pixel to be a value between the input signal value of the second sub-pixel of the second pixel and the third pixel input signal value. 
     Further, in the display device  10 D, preferably, when the pattern information indicates the second arrangement pattern, the first sub-pixel of the second pixel neighbors a side of the second sub-pixel of the second pixel in the processing direction, or the second sub-pixel of the second pixel neighbors a side of the third sub-pixel of the second pixel in the processing direction, and the correction process deciding unit decides to generate the output signal of the fourth sub-pixel of the second pixel through the correction process when the pattern information indicates the second arrangement pattern. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal value of the second sub-pixel in the second pixel to be a value between the input signal value of the first sub-pixel in the second pixel and the first pixel input signal value and causing the input signal value of the third sub-pixel in the second pixel to be a value between the input signal value of the second sub-pixel in the second pixel and the first pixel input signal value. 
     Further, in the display device  10 D, preferably, when the pattern information indicates the first arrangement pattern, the second sub-pixel of the second pixel neighbors a side of the first sub-pixel of the second pixel in the processing direction, or the third sub-pixel of the second pixel neighbors a side of the second sub-pixel of the second pixel in the processing direction, and the correction process deciding unit decides to generate the output signal of the fourth sub-pixel of the second pixel through the correction process when the pattern information indicates the first arrangement pattern. 
     Further, in the display device  10 D, preferably, the correction process deciding unit further decides whether or not the correction process is performed on the second pixel based on a magnitude relation of the rendering input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel based on the generation signal of the fourth sub-pixel of the second pixel and the input signal of the first sub-pixel, the input signal of the second sub-pixel or the input signal of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel by averaging the generation signal value of the fourth sub-pixel of the second pixel and a maximum value of the rendering input signal of the first sub-pixel, the rendering input signal of the second sub-pixel, and the rendering input signal of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel based on the generation signal of the fourth sub-pixel of the second pixel and the output signal of the fourth sub-pixel of a pixel neighboring the second pixel. 
     Further, the pixel arrangement of the display device  10 D according to the modification can be applied to the third embodiment. The display device  10 D according to the modification includes the image display panel in which a plurality of first thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the third sub-pixel and a plurality of second thinned pixels each of which includes the first sub-pixel, the second sub-pixel, and the fourth sub-pixel are arranged in the display region of the square shape having the first side and the second side intersecting with the first side in the matrix form. In the first thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along a predetermined direction to be adjacent to each other in the predetermined direction, and the third sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction serving as the direction intersecting the predetermined direction. In the second thinned pixel, the first sub-pixel and the second sub-pixel are arranged in the first arrangement along the predetermined direction to be adjacent to each other in the predetermined direction, and the fourth sub-pixel neighboring the first sub-pixel and the second sub-pixel in the intersection direction is arranged in the second arrangement neighboring the first arrangement in the intersection direction. The image display panel receives the image information of the portrait mode in which a direction along the first side is a predetermined one direction of the display image or the landscape mode in which a direction along the second side is the one direction of the display image. The display device  10 D includes the signal processing unit that generates the output signals from the input values of the input signals for the first sub-pixel, the second sub-pixel, and the third sub-pixel, and outputs the generated output signals to the image display panel. The signal processing unit includes the rendering unit that generates the rendering input signal by performing a predetermined sub-pixel rendering process of changing the signal values of the input signals of the sub-pixels of the second pixel when, in the first pixel, the second pixel neighboring the first pixel at a side in a predetermined processing direction, and the third pixel neighboring the second pixel at the side in the processing direction among the plurality of arranged pixels, the difference between the input signal values of the sub-pixels of the first pixel and the input signal values of the sub-pixels of the third pixel is a predetermined threshold value or more. The signal processing unit further includes the sub-pixel generation signal unit that generates generation signals of the first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel based on the input signal values and the rendering input signal values of the sub-pixels in each of the pixels. The signal processing unit further includes the correction process deciding unit that decides whether or not the output signal of the fourth sub-pixel of the second pixel is generated through a correction process based on a generation signal value of a neighboring sub-pixel and generation signal values of both-side sub-pixels, the neighboring subpixel is served as a sub-pixel of the second pixel neighboring the fourth sub-pixel of the second pixel in an orthogonal direction serving as a direction orthogonal to the processing direction and the both-side sub-pixels are served as a plurality of sub-pixels neighboring the neighboring sub-pixel or the fourth sub-pixel of the second pixel in the processing direction or an opposite direction serving as a direction opposite to the processing direction. The signal processing unit further includes the fourth sub-pixel output signal generating unit that performs the correction process based on the decision of the correction process deciding unit, by performing an averaging process based on the generation signal of the fourth sub-pixel of the second pixel and input signals of other sub-pixels, and generates the output signal of the fourth sub-pixel of the second pixel. The signal processing unit further includes the output signal generating unit that obtains the output signal of the first sub-pixel of the second pixel based on the rendering input signal of the first sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, obtains the output signal of the second sub-pixel of the second pixel based on the rendering input signal of the second sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient, and obtains the output signal of the third sub-pixel of the second pixel based on the rendering input signal of the third sub-pixel of the second pixel, the output signal of the fourth sub-pixel of the second pixel, and the expansion coefficient. The processing direction is a direction along the first side of the image display panel when the image information corresponds to the portrait mode and a direction along the second side of the image display panel when the image information corresponds to the landscape mode. 
     Further, in the display device  10 D, preferably, the correction process deciding unit decides whether or not the output signal of the fourth sub-pixel of the second pixel is generated based on the generation signal of the fourth sub-pixel of the second pixel when the generation signal value of the neighboring sub-pixel is smaller than the generation signal values of the both-side sub-pixels, and a difference between the generation signal value of the neighboring sub-pixel and the generation signal values of the both-side sub-pixels is a predetermined value or more. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal values of the first sub-pixel, the second sub-pixel, and the third sub-pixel of the second pixel to be a value between the first pixel input signal value and the third pixel input signal value and causing the input signal value of the second sub-pixel of the second pixel to be a value between the input signal value of the first sub-pixel of the second pixel and the input signal value of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal value of the second sub-pixel of the second pixel to be a value between the input signal value of the first sub-pixel of the second pixel and the third pixel input signal value and causing the input signal value of the third sub-pixel of the second pixel to be a value between the input signal value of the second sub-pixel of the second pixel and the third pixel input signal value. 
     Further, in the display device  10 D, preferably, the sub-pixel rendering process is a process of causing the input signal value of the second sub-pixel in the second pixel to be a value between the input signal value of the first sub-pixel in the second pixel and the first pixel input signal value and causing the input signal value of the third sub-pixel in the second pixel to be a value between the input signal value of the second sub-pixel in the second pixel and the first pixel input signal value. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel based on the generation signal of the fourth sub-pixel of the second pixel and the input signal of the first sub-pixel, the input signal of the second sub-pixel or the input signal of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel by averaging the generation signal value of the fourth sub-pixel of the second pixel and a maximum value of the rendering input signal of the first sub-pixel, the rendering input signal of the second sub-pixel, and the rendering input signal of the third sub-pixel of the second pixel. 
     Further, in the display device  10 D, preferably, the fourth sub-pixel output signal generating unit generates the output signal of the fourth sub-pixel of the second pixel based on the generation signal of the fourth sub-pixel of the second pixel and the output signal of the fourth sub-pixel of a pixel neighboring the second pixel. 
     Application Examples 
     Next, an application example of the display device  10  according to the first embodiment will be described with reference to  FIG. 35 .  FIG. 35  is a diagram illustrating an example of an electronic apparatus to which the display device according to the first embodiment is applied. The display device  10  according to the first embodiment is applicable to electronic apparatuses of all fields such as portable terminal devices such as a mobile phone illustrated in  FIG. 35  or video cameras. In other words, the display device  10  according to the first embodiment is applicable to electronic apparatuses of all fields that display video signals input from the outside or internally generated video signals as an image or video. The electronic apparatus includes the control device  11  (see  FIG. 1 ) that supplies the video signals to the display device and controls the operation of the display device. The present application example may also be applicable to the display devices according to the other embodiments and the modifications described above in addition to the display device  10  according to the first embodiment. 
     An electronic apparatus illustrated in  FIG. 35  is a portable information terminal to which the display device  10  according to the first embodiment is applied and that operates as a mobile computer, a multi-functional mobile phone, a mobile computer with a voice call function, or a mobile computer with a communication function and is also called a smartphone or a tablet terminal. The portable information terminal includes a display unit  561  on the surface of a housing  562 , for example. The display unit  561  includes the display device  10  according to the first embodiment and a touch detection (so-called a touch panel) function capable of detecting an external proximity object. 
     The exemplary embodiments according to the present invention have been described above, but the embodiments are not limited to content thereof. The components described above include components that are easily conceivable by those skilled in the art, substantially the same components, and equivalent ones. The components described above can appropriately be combined as well. In addition, various omissions, replacements or changes of the components can be made without departing from the gist of the embodiments described above.