Patent Publication Number: US-2023145390-A1

Title: Image processing device, display device, and image processing method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Provisional Application No.63/277,795, the content to which is hereby incorporated by reference into this application. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The disclosure relates to an image processing device, a display device, and an image processing method. 
     2. Description of the Related Art 
     JP 2019-174742 A discloses a liquid crystal display device in which a plurality of liquid crystal panels are arranged in an overlapping manner. In the liquid crystal display device disclosed in JP 2019-174742 A, a second liquid crystal panel arranged on the back surface side of a first liquid crystal panel displays an image using image data obtained by expanding a bright spot signal included in an input video signal. 
     SUMMARY 
     When an image including a plurality of overlapping images is displayed, if the plurality of images are displayed with their luminance uniformly adjusted, the display quality might be compromised due to a noticeable difference in brightness between some of the images displayed and other images. For example, the display quality might be compromised with some of the displayed images being too bright. 
     In the liquid crystal display device disclosed in JP 2019-174742 A, the bright spot signals are uniformly adjusted for the image displayed on the second liquid crystal panel. Thus, when the liquid crystal display device disclosed in JP 2019-174742 A displays a plurality of videos in an overlapping manner, the display quality might be compromised due to some images in the displayed video being too bright. In view of the above, an object of one aspect of the disclosure is to provide an image processing device, a display device, and an image processing method suppressing the deterioration of the display quality when a plurality of images are displayed in an overlapping manner. 
     An image processing device according to an aspect of the disclosure in a display device including a first liquid crystal panel configured to display a first image and a second liquid crystal panel that is disposed on a back surface of the first liquid crystal panel and is configured to display a second image, includes: a first image generation unit configured to generate the first image from an input image in which a fourth image is overlapped on a third image, an image in a first region included in the first image forming the fourth image; a second image generation unit configured to generate the second image from the input image, an image in a second region included in the second image forming the fourth image; and an adjustment unit configured to reduce a luminance in the second region in the second image to reduce a luminance of the fourth image, with an amount of reduction of the luminance in the second region being larger than an amount of reduction of a luminance in the first region. 
      A display device according to an aspect of the disclosure includes: a first liquid crystal panel configured to display the first image; a second liquid crystal panel that is disposed on a back surface of the first liquid crystal panel and is configured to display a second image; and an image processing device. The image processing device includes: a first image generation unit configured to generate the first image from an input image in which a fourth image is overlapped on a third image, an image in a first region included in the first image forming the fourth image; a second image generation unit configured to generate the second image from the input image, an image in a second region included in the second image forming the fourth image; and an adjustment unit configured to reduce a luminance in the second region in the second image to reduce a luminance of the fourth image, with an amount of reduction of the luminance in the second region being larger than an amount of reduction of a luminance in the first region. 
     An image processing method of generating a first image displayed on a first liquid crystal panel and a second image displayed on a second liquid crystal panel disposed on a back surface of the first liquid crystal panel according to an aspect of the disclosure includes: generating the first image from an input image in which a fourth image is overlapped on a third image, an image in a first region included in the first image forming the fourth image; generating the second image from the input image, an image in a second region included in the second image forming the fourth image; and reducing a luminance in the second region in the second image to reduce the luminance of the fourth image, with an amount of reduction of the luminance in the second region being larger than an amount of reduction of a luminance in the first region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram illustrating an example of a configuration of a display device according to a first embodiment. 
         FIG.  2    is an exploded perspective view illustrating an example of a schematic configuration of a first liquid crystal panel, a second liquid crystal panel, and a backlight. 
         FIG.  3    is a diagram for explaining a first region included in a first image. 
         FIG.  4    is a diagram for explaining a second region included in a second image. 
         FIG.  5    is a flowchart illustrating an example of an operation performed by an image processing device according to the first embodiment. 
         FIG.  6 A  illustrates an example of a third image. 
         FIG.  6 B  illustrates an example of a fourth image. 
         FIG.  6 C  illustrates an example of an input image with the fourth image illustrated as an example in  FIG.  6 B  overlapped on the third image illustrated as an example in  FIG.  6 A . 
         FIG.  7 A  illustrates an example of an image obtained by reducing the gray-scale number in the first region in the first image generated from the input image illustrated as an example in  FIG.  6 C . 
         FIG.  7 B  illustrates an example of the second image generated from the input image illustrated as an example in  FIG.  6 C . 
         FIG.  7 C  is a diagram illustrating a comparative example of the display device according to the first embodiment, and illustrates an example of an image in which the image illustrated as an example in  FIG.  7 A  and the second image illustrated as an example in  FIG.  7 B  are overlapped to be viewed. 
         FIG.  8 A  illustrates an example of the first image generated from the input image illustrated as an example in  FIG.  6 C . 
         FIG.  8 B  illustrates an example of the second image obtained by reducing the luminance for the second region in the second image generated from the input image illustrated as an example in  FIG.  6 C . 
         FIG.  8 C  is a diagram illustrating an example of an image in which the first image illustrated as an example in  FIG.  8 A  and the second image illustrated as an example in  FIG.  8 B  are overlapped and viewed. 
         FIG.  9    is a block diagram illustrating an example of a configuration of a display device according to a modified example of the first embodiment. 
         FIG.  10    is a block diagram illustrating an example of a configuration of a display device according to a second embodiment. 
         FIG.  11    is a flowchart illustrating an example of an operation performed by the display device according to the second embodiment. 
         FIG.  12    is a block diagram illustrating an example of a configuration of a display device according to a modified example of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     First Embodiment 
     A first embodiment will be described with reference to  FIG.  1    to  FIG.  8 C . Note that, in the drawings, identical or equivalent elements are given an identical reference sign, and redundant descriptions thereof may be omitted. 
       FIG.  1    is a block diagram illustrating an example of a configuration of a display device  100  according to the present embodiment. The display device  100  includes a first liquid crystal panel  101 , a second liquid crystal panel  102 , a backlight  103 , an image processing device  104 , a first timing control unit  105 , and a second timing control unit  106 .  FIG.  2    is an exploded perspective view illustrating an example of a schematic configuration of the first liquid crystal panel  101 , the second liquid crystal panel  102 , and the backlight  103 . 
     The first liquid crystal panel  101  is a liquid crystal panel having a display region for displaying various images, where a plurality of pixels are arranged in a matrix. The first liquid crystal panel  101  drives the liquid crystals by an electric field generated by voltage supplied to each pixel. The first liquid crystal panel  101  displays an image, by controlling the light transmittance of the backlight  103  in the liquid crystals driven. The first liquid crystal panel  101  includes subpixels of RGB (red, green, and blue). 
     The second liquid crystal panel  102  is a liquid crystal panel having a display region for displaying various images, where a plurality of pixels are arranged in a matrix. The second liquid crystal panel  102  drives the liquid crystals by an electric field generated by a voltage supplied to each pixel. The second liquid crystal panel  102  displays an image, by controlling the light transmittance of the backlight  103  in the liquid crystals driven. The maximum gray-scale number displayable by the second liquid crystal panel  102  may be lower than that displayable by the first liquid crystal panel  101 . For example, the second liquid crystal panel  102  includes a subpixel of W (white) without including the subpixels of RGB. The second liquid crystal panel  102  may include the subpixels of RGB (red, green, and blue). The resolution of the second liquid crystal panel  102  and the resolution of the first liquid crystal panel  101  may be the same or different. For example, the resolution of the second liquid crystal panel  102  is lower than the resolution of the first liquid crystal panel  101 . 
      The second liquid crystal panel  102  is disposed on the back surface of the first liquid crystal panel  101  as viewed from the user side, and is disposed to overlap with the first liquid crystal panel  101 . Thus, the second liquid crystal panel  102  is disposed on the back surface side of the display surface of the first liquid crystal panel  101 , while overlapping with the first liquid crystal panel  101 . 
     The backlight  103  is disposed on the back surface side of the display surface of the second liquid crystal panel  102  to overlap with the second liquid crystal panel  102 , and is an illumination device that planarly illuminates the first liquid crystal panel  101  and the second liquid crystal panel  102 . 
     The second liquid crystal panel  102  is disposed between the first liquid crystal panel  101  and the backlight  103 , to modulate the light from the backlight  103 , and illuminate the first liquid crystal panel  101 . Thus, the first liquid crystal panel  101  receives the light modulated by the second liquid crystal panel  102 , and thus can display an image with a high contrast. 
     The image processing device  104  adjusts the luminance of a first image  124  displayed on the first liquid crystal panel  101  and the luminance of a second image  125   b  displayed on the second liquid crystal panel  102 . The image processing device  104  is implemented, for example, by a circuit such as an Application Specific Integrated Circuit (ASIC) or a Field-Programmable Gate Array (FPGA). In the disclosure, the image is two-dimensional data including RGB pixel data In the disclosure, the luminance is a value indicating the brightness obtained with pixels lit. 
      The image processing device  104  includes an image acquisition unit  111 , an image combining unit  112 , a first image generation unit  113 , a second image generation unit  114 , a parameter unit  115 , and an adjustment unit  116 . 
     The image acquisition unit  111  acquires a third image  121  included in one video and a fourth image  122  included in another video. In the disclosure, the video is a signal indicating a plurality of images in time series. 
     The image combining unit  112  uses mask region information  126   b  described below, to generate an input image  123  with the fourth image  122  overlapped on the third image  121 . 
     The first image generation unit  113  generates the first image  124  from the input image  123 . An image in a first region included in the first image  124  forms the fourth image  122 . An image outside the first region included in the first image  124  forms the third image  121   
     The second image generation unit  114  generates a second image  125   a  from the input image  123 . An image in a second region included in the second image  125   a  forms the fourth image  122 . An image outside the second region included in the second image  125   a  forms the third image  121 . 
     The parameter unit  115  holds mask region information  126   a  and the mask region information  126   b . The mask region information  126   a  and the mask region information  126   b  indicate the position and the size of the second region. The mask region information  126   a  and the mask region information  126   b  may be, for example, (1) coordinates at the upper left and lower right of the second region, or (2) coordinates at the upper left of the second region and the width and height of the second region. The mask region information  126   a  and the mask region information  126   b  may be the same or may be different from each other. For example, the mask region information  126   a  may be the information (1) and the mask region information  126   b  may be the information (2), or the mask region information  126   a  and the mask region information  126   b  may both be the information (1). The mask region information  126   a  and the mask region information  126   b  may be hereinafter collectively referred to as mask region information  126 . Upon acquiring control information  127  indicating the position and size of the second region, the parameter unit  115  changes the mask region information  126  based on the position and size indicated by the control information  127 . 
     The adjustment unit  116  uses the mask region information  126   a  to reduce the luminance in the second region in the second image  125   a , and thus reduces the luminance of the fourth image  122 . 
     The first timing control unit  105  drives the first liquid crystal panel  101 . The first timing control unit  105  controls the timing at which the first image  124  is displayed on the first liquid crystal panel  101 . 
     The second timing control unit  106  drives the second liquid crystal panel  102 . The second timing control unit  106  controls the timing at which the second image  125   b  with the luminance in the second region reduced is displayed on the second liquid crystal panel  102 . 
       FIG.  3    is a diagram for explaining a first region  301  included in the first image  124 . Pixel coordinates in a horizontal direction and a vertical direction of the first image  124  are defined as x1 and y1. Under this condition, the coordinates of the pixel at the upper left end of the first image  124  are (x1,y1) = (0,0). The coordinates of the pixel at the lower right end of the first image  124  are (x1,y1) = (x13,y13). The coordinates of the pixel at the upper left end of the first region  301  included in the first image  124  are (x1,y1) = (x11,y11). The coordinates of the pixel at the lower right end of the first region  301  are (x1,y1) = (x12,y12). The fourth image  122  is formed in a range of x11 ≤ x1 ≤ x12 and y11 ≤ y1 ≤ y12, which is in the first region  301 . On the other hand, in the first image  124 , the third image  121  is configured in the range outside the first region  301 . 
       FIG.  4    is a diagram for explaining a second region  401  included in the second image  125   a . Pixel coordinates in a horizontal direction and a vertical direction of the second image  125   a  are respectively defined as x2 and y2. Under this condition, the coordinates of the pixel at the upper left end of the second image  125   a  are (x2,y2) = (0,0). The coordinates of the pixel at the lower right end of the second image  125   a  are (x2,y2) = (x23,y23) The coordinates of the pixel at the upper left end of the second region  401  included in the second image  125   a  are (x2,y2) = (x21,y21). The coordinates of the pixel at the lower right end of the second region  401  are (x2,y2) = (x22,y22). The fourth image  122  is formed in a range of x21 ≤ x2 ≤ x22 and y21 ≤ y2 ≤ y22, which is in the second region  401 . On the other hand, in the second image  125   a , the third image  121  is configured in the range outside the second region  401 . 
       FIG.  5    is a flowchart illustrating an example of an operation performed by the image processing device  104  according to the present embodiment. 
      In step S 501 , the image acquisition unit  111  acquires the third image  121  included in one video and the fourth image  122  included in another video. 
     In step S 502 , the image combining unit  112  generates the input image  123  with the fourth image  122  acquired in step S 501  overlapped on the third image  121  acquired in step S 501 . 
     In step S 503 , the second image generation unit  114  generates the second image  125   a  from the input image  123 . Specifically, the second image generation unit  114  converts the input image  123  into an image with a resolution displayable on the second liquid crystal panel  102 , and then executes filter processing based on a viewing angle to generate the second image  125   a . 
     In step S 504 , the first image generation unit  113  generates the first image  124  from the input image  123  and the second image  125   a . Specifically, the first image generation unit  113  multiplies the light transmittance of the first liquid crystal panel by the light transmittance of the second liquid crystal panel, to generate the first image  124  in such a manner that the input image is displayed upon being lit by the backlight. For example, the first image  124  is an image with pixels each indicating the pixel value of a first gray-scale number of a red component R, a green component G, and a blue component B. In the disclosure, the pixel value is a data value representing the brightness of each pixel. 
     In step S 505 , the adjustment unit  116  determines an adjustment amount a for the luminance in the second region  401  included in the second image  125   a . Note that the adjustment unit  116  determines the position and the size of the second region  401  based on the mask region information  126 . For example, the adjustment unit  116  acquires the set adjustment amount α to determine the adjustment amount a for the luminance in the second region  401  included in the second image  125   a . 
     Alternatively, the adjustment unit  116  may acquire the adjustment amount a input from the outside of the display device  100 . For example, when the user uses a button, a remote controller, and the like provided with the display device  100  to input the adjustment amount α, the adjustment unit  116  determines the adjustment amount α for the luminance in the second region  401  included in the second image  125   a  by acquiring the adjustment amount α thus input. 
     Alternatively, the adjustment unit  116  may determine the adjustment amount a for the luminance of each pixel in the second region  401  based on the luminance of each pixel in the second region  401 . For example, the adjustment unit  116  calculates the adjustment amount α for the luminance by using a formula for the adjustment amount α = f (Y i2 (x2,y2)) for the luminance. The luminance Y i2 (x2,y2) indicates the luminance corresponding to a coordinate value (x2,y2) in the second image  125   a . The function f is a formula for calculating the adjustment amount a for the luminance from the luminance Y i2 (x2,y2). The adjustment unit  116  substitutes the luminance Y i2 (x2,y2) in the function f to calculate the adjustment amount a for the luminance. 
     In step S 506 , the adjustment unit  116  applies the adjustment amount a for the luminance determined in step S 505  to the luminance Y i2 (x2,y2) in the second region  401 , and thus reduces the luminance Y i2 (x2,y2) in the second region  401 . The adjustment unit  116  reduces the luminance Y i2 (x2,y2) in the second region  401  to reduce the luminance of the fourth image  122  included in the second image  125   a . For example, the adjustment unit  116  applies the set adjustment amount α to the luminance Y i2 (x2,y2) in the second region  401  to reduce the luminance Y i2 (x2,y2) in the second region  401 , and thus reduces the luminance of the fourth image  122  included in the second image  125   a . 
     It is assumed that the adjustment unit  116  has alternatively acquired the adjustment amount α input from the outside. In this case, the adjustment unit  116  applies the adjustment amount a for the luminance input from the outside to the luminance Y i2 (x2,y2) in the second region  401 , and thus reduces the luminance Y i2 (x2,y2) in the second region  401 . 
     It is assumed that the adjustment unit  116  has alternatively determined the adjustment amount α for the luminance of each pixel in the second region  401  based on the luminance Y i2 (x2,y2) of each pixel in the second region  401 . In this case, the adjustment unit  116  applies the adjustment amount a for the luminance of each pixel in the second region  401  determined based on the luminance Y i2 (x2,y2) of each pixel in the second region  401 , to the luminance Y i2 (x2,y2) of each pixel in the second region  401 , to reduce the luminance Y i2 (x2,y2) in the second region  401 . For example, the adjustment unit  116  multiplies the luminance Y i2 (x2,y2) of each pixel in the second region  401  by the adjustment amount α calculated, to reduce the luminance of each pixel in the second region  401 . In this manner, the adjustment unit  116  reduces the luminance of each pixel in the second region  401 , based on the luminance of each pixel in the fourth image  122 . 
     When the adjustment amount α &lt; 1 for the luminance, x21 ≤ x ≤ x22, and y21 ≤ y ≤ y22 hold, the luminance Y O2 (x2,y2) = α × Y i2 (x2,y2) holds The luminance Y O2  is the luminance of the pixel at the coordinates (x2,y2) included in the second image  125   b  displayed on the second liquid crystal panel  102 . Thus, the luminance outside the second region  401  included in the second image  125   b  is lower than the luminance outside the second region  401  included in the second image  125   a . On the other hand, when x2 &lt; x21 or x2 &gt; x22 holds or y2 &lt; y21 or y2 &gt; y22 holds, Y O2 (x2,y2) = Y i2 (x2,y2) holds. Thus, the luminance outside the second region  401  included in the second image  125   b  is the same as the luminance outside the second region  401  included in the second image  125   a . 
     In step S 507 , the first timing control unit  105  outputs the first image  124  generated in step S 504 , to the first liquid crystal panel  101 . 
     In step S 508 , the second timing control unit  106  outputs the second image  125   b  with the luminance in the second region  401  reduced in step S 506 , to the second liquid crystal panel  102 . 
       FIG.  6 A  to  FIG.  6 C  are diagrams illustrating examples of the third image  121 , the fourth image  122 , and the input image  123 .  FIG.  6 A  illustrates an example of the third image  121 .  FIG.  6 B  illustrates an example of the fourth image  122 .  FIG.  6 C  illustrates an example of the input image  123  with the fourth image  122  illustrated as an example in  FIG.  6 B  overlapped on the third image  121  illustrated as an example in  FIG.  6 A . 
     For example, the third image  121  is an image with the gray-scale number of each of the red component, the green component, and the blue component being eight bits. In this case, in the brightest portion in the third image  121 , the pixel value of each of the red component, the green component, and the blue component is 255. For example, the fourth image  122  is an image with the gray-scale number of each of the red component, the green component, and the blue component being eight bits. In this case, in the brightest portion in the fourth image  122 , the pixel value of each of the red component, the green component, and the blue component is 255. 
     In the input image  123  illustrated as an example in  FIG.  6 C , the luminance is the same between the brightest portion of the third image  121  and the brightest portion of the fourth image  122 . For example, when the input image  123  illustrated as an example in  FIG.  6 C  is input to be displayed on a liquid crystal panel with a maximum luminance of 1000 nits, the luminance of the brightest portions of the third image  121  and the fourth image  122  is 1000 nits. In this case, the fourth image  122  displayed on the liquid crystal panel could be too bright, and thus could be an image with low visibility. 
       FIG.  7 A  to  FIG.  7 C  are diagrams illustrating a comparative example corresponding to a case where the processing of the present embodiment is not applied.  FIG.  7 A  illustrates an example of the first image  124 , generated from the input image  123  illustrated as an example in  FIG.  6 C , with the gray-scale number of the first region  301  reduced, to make the fourth image  122  darker and easier to view  FIG.  7 B  illustrates an example of the second image  125   a  generated from the input image  123  illustrated as an example in  FIG.  6 C .  FIG.  7 C  is a diagram illustrating an example of an image in which the first image  124  illustrated as an example in  FIG.  7 A  and the second image  125   a  illustrated as an example in  FIG.  7 B  are overlapped and viewed. 
     The reduction of the gray-scale number for the first region  301  included in the first image  124  can solve the problem of the fourth image  122  becoming too bright but leads to another problem. Specifically, the effective gray-scale number in a region forming the fourth image  122  is reduced and a false contour becomes visible in a gray-scale portion in the fourth image  122  as illustrated as an example in  FIG.  7 C . As a result, the display quality is compromised compared with that of the fourth image  122  illustrated as an example in  FIG.  6 C . Considering the above, the reduction of the gray-scale number for the first region  301  included in the first image  124  might result in an image that is difficult to view due to the display quality being relatively compromised. 
       FIG.  8 A  to  FIG.  8 C  are diagrams illustrating an example of processing executed by the image processing device  104  according to the present embodiment.  FIG.  8 A  illustrates an example of the first image  124  generated from the input image  123  illustrated as an example in  FIG.  6 C .  FIG.  8 B  illustrates an example of the second image  125   b  obtained by reducing the luminance of the second region  401  in the second image  125   a  generated from the input image  123  illustrated as an example in  FIG.  6 C .  FIG.  8 C  is a diagram illustrating an example of an image in which the first image  124  illustrated as an example in  FIG.  8 A  and the second image  125   b  illustrated as an example in  FIG.  8 B  are overlapped and viewed. 
     As illustrated as an example in  FIG.  8 C , the display device  100  reduces the luminance of the second region  401  in the second image  125   b  displayed on the second liquid crystal panel  102 , without changing the gray-scale number of the first region  301  included in the first image  124  displayed on the first liquid crystal panel  101 . When the display device  100  reduces the luminance of the second region  401  included in the second image  125   b  displayed on the second liquid crystal panel  102  as illustrated as an example in  FIG.  8 C , the change in the gray scale in a region forming the fourth image  122  can be made smooth in the image viewed. Furthermore, the display device  100  does not change the gray-scale number of the first region  301  included in the first image  124 . Thus, the deterioration of the display quality can be suppressed for a region forming the fourth image  122  as illustrated as an example in  FIG.  8 C . 
     Furthermore, the display device  100  can reduce a difference in brightness between a region forming the third image  121  and a region forming the fourth image  122  in an image viewed, as illustrated as an example in  FIG.  8 C . According to such effects, the display device  100  has two liquid crystal display panels overlapping, to improve the contrast of an image viewed and to reduce the luminance of the second region  401  included in the second image  125   b , whereby deterioration of the display quality due to overlapping display of a plurality of images can be suppressed, so that an image that is easy to view by the user can be displayed. 
     In the present embodiment, the adjustment unit  116  reduces the luminance of the fourth image  122  by reducing the luminance in the second region  401  included in the second image  125   a , but does not execute processing of reducing the luminance for the first region  301  included in the first image  124 . In the processing executed by the image processing device  104  according to the present embodiment, the amount of reduction of the luminance in the second region  401  can be regarded as being larger than the amount of reduction of the luminance in the first region  301 . This allows the image processing device  104  according to the present embodiment to display the first region  301  included in the first image  124  without reducing the gray-scale range while reducing the display luminance of the fourth image  122 , whereby generation of a false contour can be suppressed so that the deterioration of the display quality can be suppressed. 
     Modified Example 
     As a modified example of the present embodiment, the input image  123  in which the fourth image  122  is overlapped on the third image  121  may be input to the image processing device  104 .  FIG.  9    is a block diagram illustrating an example of a configuration of a display device  100  according to the present modified example. The configuration of the display device  100  illustrated as an example in  FIG.  9    is different from the configuration of the display device  100  illustrated as an example in  FIG.  1   , in that the display device  100  illustrated as an example in  FIG.  9    does not include the image combining unit  112 . In the display device  100  according to the present modified example, the input image  123  is input from the outside of the image processing device  104  to the first image generation unit  113  and the second image generation unit  114 . 
     When the input image  123  in which the fourth image  122  is overlapped on the third image  121  is input, the display device  100  according to the present modified example reduces the luminance of the second region  401  included in the second image  125   a  to reduce the luminance of the fourth image  122  included in the second image  125   a . The luminance for a region forming the fourth image  122 , which is a part of the input image  123 , is adjusted. With this configuration, even when the input image  123  in which the fourth image  122  is overlapped on the third image  121  is input, the display device  100  according to the present modified example can suppress the deterioration of the display quality due to the overlapping display of the plurality of images. 
     Second Embodiment 
     A second embodiment will be described with reference to  FIG.  10    and  FIG.  11   . Note that, in the drawings, identical or equivalent elements are given an identical reference sign, and redundant descriptions thereof may be omitted. The configurations and processes having substantially the same functions as in the first embodiment are denoted by the same reference numerals and the descriptions thereof will be omitted. Differences from the first embodiment will be described. 
       FIG.  10    is a block diagram illustrating an example of a configuration of a display device  100  according to the present embodiment. The display device  100  illustrated as an example in  FIG.  10    is different from the display device  100  illustrated as an example in  FIG.  1    in that the display device  100  illustrated as an example in  FIG.  10    includes an adjustment unit  1001  instead of the adjustment unit  116 . 
     The mask region information  126   a  and the mask region information  126   b  according to the present embodiment indicate the positions and sizes of the first region  301  and the second region  401 . The mask region information  126   a  and the mask region information  126   b  according to the present embodiment may be, for example, (1) the coordinates at the upper left and lower right of the first region  301  and the second region  401 , or (2) the coordinates at the upper left of the first region  301  and the second region  401 , and the widths and the heights of the first region  301  and the second region  401 . The mask region information  126   a  and the mask region information  126   b  may be the same or may be different from each other. For example, the mask region information  126   a  may be the information (1) and the mask region information  126   b  may be the information (2), or the mask region information  126   a  and the mask region information  126   b  may both be the information (1). Upon acquiring the control information  127  indicating the positions and sizes of the first region  301  and the second region  401 , the parameter unit  115  changes the mask region information  126  based on the position and size indicated by the control information  127 . 
     The adjustment unit  1001  uses the mask region information  126   a  to reduce the luminance in the first region  301  in a first image  124   a , and thus reduces the luminance of the fourth image  122  included in the first image  124   a . Furthermore, the adjustment unit  1001  reduces the luminance of the fourth image  122  included in the second image  125   a   by reducing the luminance in the second region  401  in the second image  125   a  Specifically, the adjustment unit  1001  reduces the luminance in the first region  301  and the luminance in the second region  401 , with the amount of reduction of the luminance in the second region  401  being larger than the amount of reduction of the luminance in the first region  301 . 
       FIG.  11    is a flowchart illustrating an example of an operation performed by the display device  100  according to the present embodiment. The processes in steps S 1101  to S 1104  illustrated as an example in  FIG.  11    are the same as those in steps S 501  to S 504  illustrated as an example in  FIG.  5   , and thus detailed descriptions thereof will be omitted. 
     In step S 1105 , the adjustment unit  1001  determines an adjustment amount α1 for the luminance in the first region  301 . In step S 1106 , the adjustment unit  1001  determines an adjustment amount a2 for the luminance in the second region  401 . 
     In step S 1107 , the adjustment unit  1001  applies the adjustment amount α1 for the luminance in the first region  301 , determined in step S 1105 , to the luminance Y i1 (x1,y1) in the first region  301  included in the first image  124   a  to reduce the luminance Y i1 (x1,y1) in the first region  301 . Note that the adjustment unit  1001  determines the position and size of the first region  301  based on the mask region information  126 . The adjustment unit  1001  reduces the luminance Y i1 (x1,y1) in the first region  301  to reduce the luminance of the fourth image  122  included in the first image  124   a . 
     For example, the adjustment unit  1001  applies the set adjustment amount α1 for the luminance to the luminance Y i1 (x1,y1) in the first region  301 , and thus reduces the luminance Y i1 (x1,y1) in the first region  301 . Alternatively, the adjustment unit  1001  may apply the adjustment amount α1 for the luminance input from the outside to the luminance in the first region  301 , and thus reduce the luminance Y i1 (x1,y1) in the first region  301 . Alternatively, the adjustment unit  1001  may apply the adjustment amount α1 for the luminance of each pixel in the first region  301  determined based on the luminance Y i1 (x1,y1) of each pixel in the first region  301 , to the luminance Y i1 (x1,y1) of each pixel in the first region  301 , and thus reduce the luminance Y i1 (x1,y1) in the first region  301 . 
     Specifically, when the adjustment amount α1 ≤ 1 for the luminance in the first region  301  holds and x11 ≤ x ≤ x12 and y11 ≤ y ≤ y12 hold, the luminance Y O1 (x1,y1)= a1 × Y i1 (x1,y1) holds. The luminance Yoi is the luminance of the pixel at the coordinates (x1,y1) included in a first image  124   b . Thus, the luminance in the first region  301  of the first image  124   b  is not higher than the luminance in the first region  301  of the first image  124   a . On the other hand, when x1 &lt; x11 or x1 &gt; x12 holds or y1 &lt; y11 or y1 &gt; y12 holds, Y O1 (x1,y1) = Y i1 (x1,y1) holds. Thus, the luminance outside the first region  301  of the first image  124   b  is the same as the luminance outside the first region  301  of the first image  124   a . Note that when the adjustment amount α = 1 for the luminance in the first region  301  holds, the first image  124   b  is the same as the first image  124   a . 
     In step S 1108 , the adjustment unit  1001  applies the adjustment amount a2 for the luminance in the second region  401 , determined in step S 1106 , to the luminance Y i2 (x2,y2) in the second region  401  included in the second image  125   a , and thus reduces the luminance Y i2 (x2,y2) in the second region  401 . Note that the adjustment unit  1001  determines the position and size of the second region  401  based on the mask region information  126 . The adjustment unit  1001  reduces the luminance of the fourth image  122  included in the second image  125   a  by reducing the luminance Y i2 (x2,y2) of the second region  401 . 
     For example, the adjustment unit  1001  applies the set adjustment amount α2 for the luminance to the luminance in the second region  401 , and thus reduces the luminance Y i2 (x2,y2) in the second region  401 . Alternatively, the adjustment unit  1001  may apply the adjustment amount α2 for the luminance input from the outside to the luminance Y i2 (x2,y2) in the second region  401 , and thus reduce the luminance Y i2 (x2,y2) in the second region  401 . Alternatively, the adjustment unit  1001  may apply an adjustment amount α2 for the luminance of each pixel in the second region  401 , determined in accordance with the luminance Y i2 (x2,y2) of each pixel in the second region  401  to the luminance Y i2 (x2,y2) of each pixel in the second region  401 , and thus reduce the luminance Y i2 (x2,y2) in the second region  401 . In the adjustment unit  1001 , when the product of the adjustment amount α1 for the luminance in the first region  301  and the adjustment amount α2 for the luminance in the second region  401  matches the adjustment amount a for the luminance in the first embodiment, the viewed display quality achieved by the display device  100  of the present embodiment is equivalent to the viewed display quality achieved by the display device  100  of the first embodiment When the adjustment amount α1 for the luminance in the first region  301  is set to be 1 and the adjustment amount α2 for the luminance in the second region  401  is set to be the adjustment amount α for the luminance in the first embodiment with the adjustment unit  1001 , the processing result obtained by the display device  100  of the present embodiment is the same as the processing result obtained by the display device  100  of the first embodiment. 
     Furthermore, the adjustment unit  1001  reduces the luminance in the first region  301  and the luminance in the second region  401 , with the amount of reduction of the luminance in the second region  401  being larger than the amount of reduction of the luminance in the first region  301 . Thus, the adjustment unit  1001  can suppress reduction of the effective gray-scale number of a region forming the fourth image  122  in the first image  124   b  displayed on the first liquid crystal panel  101 . 
     In step S 1109 , the first timing control unit  105  outputs the first image  124   b  with the luminance of the first region  301  reduced in step S 1107 , to the first liquid crystal panel  101 . 
     In step S 1110 , the second timing control unit  106  outputs the second image  125   b  with the luminance in the second region  401  in the fourth image  122  reduced in step S 1108 , to the second liquid crystal panel  102 . 
     In the present embodiment, as described above, the adjustment unit  1001  reduces the luminance in the first region  301  and the luminance in the second region  401 , with the amount of reduction of the luminance in the second region  401  in the second image  125   b  being larger than the amount of reduction of the luminance in the first region  301  in the first image  124   b . With this configuration, the image processing device  104  according to the present embodiment can display the first region  301  included in the first image  124   b  with a wider gray-scale range than the second region  401  in the second image  125   b  while reducing the display luminance of the fourth image  122 , whereby generation of a false contour can be suppressed, and the deterioration of the display quality can be suppressed. 
     As described above, the display device  100  reduces the luminance of the fourth image  122  with the amount of reduction of the luminance for the second region  401  included in the second image  125   b  being larger than the amount of reduction of the luminance for the first region  301  included in the first image  124   b , and thus can suppress the deterioration of the display quality due to overlapping display of a plurality of images, and can display an image that is easy to view. 
     Modified Example 
     In a modified example of the present embodiment, the input image  123  may be input to the image processing device  104 .  FIG.  12    is a block diagram illustrating an example of a configuration of a display device  100  according to the present modified example. The configuration of the display device  100  illustrated as an example in  FIG.  12    is different from the configuration of the display device  100  illustrated as an example in  FIG.  1   , in that the display device  100  illustrated as an example in  FIG.  12    does not include the image combining unit  112 . In the display device  100  according to the present modified example, the input image  123  is input from the outside of the image processing device  104  to the first image generation unit  113  and the second image generation unit  114 . 
     When the input image  123  is input, the display device  100  according to the present modified example reduces the luminance of the fourth image  122 , with the amount of reduction of the luminance for the second region  401  included in the second image  125   b  being larger than the amount of reduction of the luminance for the first region  301  included in the first image  124   b . With this configuration, the display device  100  according to the present modified example can suppress the deterioration of the display quality due to the overlapping display of a plurality of images, and thus can display an image that is easy to view 
     The disclosure is not limited to each of the embodiments described above, and various modifications may be made within the scope of the claims. Embodiments obtained by appropriately combining technical approaches disclosed in each of the different embodiments also fall within the technical scope of the present invention. Moreover, novel technical features may be formed by combining the technical approaches disclosed in each of the embodiments.