Patent Publication Number: US-2010110094-A1

Title: Display control device, display device, and display control method

Description:
TECHNICAL FIELD 
     The present invention relates to a display control device, a display device, and a display control method each having a so-called multi-view display function displaying different images to be respectively visible, from different viewing directions, on a common display screen. 
     BACKGROUND ART 
     As a display control device with a so-called multi-view display having a common display screen, on which different images are respectively visible from different viewing directions, there has been known a multi-view display with a liquid crystal panel having a parallax barrier on the front side thereof. Different information (images) can be displayed on the right and left sides of the display screen by separating directions of lights through a backlight on a pixel basis (for example, as disclosed in Patent Document 1). Such a display control device is mounted on a vehicle, allowing the front-seat passenger to watch a TV program or another image, while the driver is checking a navigation map image. 
     [8 Patent Document 1] Japanese Unexamined Patent Publication No. 2005-78080 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the above-mentioned display control device, a so-called crosstalk occurs such that the both of right and left images are mixed according to a direction from which the display screen is watched. For example, while the driver is watching the navigation image, when the TV image of the front passenger&#39;s seat side leaks out to the driver&#39;s seat side and overlaps with the navigation image, there is a possibility that the driver cannot distinguish navigation information clearly. 
     The present invention has been made in view of the above described problems, and it is an object of the present invention to provide a display control device, a display device, and a display control method which can reduce crosstalk of images and improve the visibility of images. 
     Means for Solving the Problems 
     The above object is achieved by a display control device characterized by including: comparison means that compares a luminance of a first image with a luminance of a second image in units of pixel; interpolation means that interpolates a pixel value, having a luminance smaller than an attention pixel of at least one of the first image and the second image, to said at least one of the first image and the second image, when a difference in luminance between an attention pixel of the first image and an attention pixel of the second image is equal to or greater than a first threshold value; and display control means that displays the first image and the second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions. 
     The present invention reduces the difference in luminance between the first image and the second image. This reduces the crosstalk of images and improves the visibility of the images. 
     In the above configuration, the interpolation means may directly output pixel values of attention pixels of the first image data and the second image data to the display control means, when the difference in luminance between the attention pixel of the first image and the attention pixel of the second image is smaller than the first threshold value. 
     Therefore, only the luminance of the pixel having a large difference in luminance is reduced, thereby reducing the crosstalk. 
     A display control device according to the present invention includes: comparison means that compares a luminance of a first image with a luminance of a second image on a pixel basis; interpolation means that interpolates a black pixel in at least one of the first image and the second image, when a difference in luminance between an attention pixel of the first image and an attention pixel of the second image is equal to or greater than a second threshold value, and that interpolates a pixel value, having a luminance smaller than the attention pixel of at least one of the first image and the second image, in said at least one of the first image and the second image, when the difference in luminance between the attention pixel of the first image and the attention pixel of the second image is equal to or greater than a third threshold value, the third threshold value being smaller than the second threshold value; and display control means that displays the first image and the second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions. 
     The present invention reduces the difference in luminance between the first image and the second image. This reduces the crosstalk of images and improves the visibility of the images. 
     A display control device according to the present invention includes: comparison means that compares a luminance of a first image with a luminance of a second image in units of pixel; interpolation means that interpolates a pixel value that is adjusted based on a difference in luminance between an attention pixel of the first image and an attention pixel of the second image in at least one of the first image and the second image; and display control means that displays the first image and the second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions. 
     The present invention reduces the difference in luminance between the first image and the second image. This reduces the crosstalk of images and improves the visibility of the images. 
     In the above configuration, the comparison means may compare the luminance of the first image with the luminance of the second image by comparing a luminance of an RGB signal of the first image with a luminance of an RGB signal of the second image. 
     This compares the luminance of the first image with that of the second image with accuracy. 
     In the above configuration, the interpolation means may interpolate the pixel value having the luminance smaller than the attention pixel in the first image data and the second image data for every given frames. 
     This simplifies a process. 
     A display control device according to the present invention includes: comparison means that compares a luminance of a first image with a luminance of a second image for every block with a given size; interpolation means that interpolates a block of an image, having a luminance smaller than a block to be compared with, of at least one of the first image and the second image, in said at least one of the first image and the second image, when a difference in luminance between a block of the first image and a block of the second image is a first threshold value; and display control means that displays the first image and the second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions. 
     The present invention reduces the difference in luminance between the first image and the second image. This reduces the crosstalk of images and improves the visibility of the images. Additionally, the control is performed in units of a given block, thereby simplifying a process. 
     In the above configuration, the comparison means may compare the luminance by determining an average value or a maximum value of each luminance of blocks, to be compared with, of the first image and the second image. 
     This compares the luminance of the first image with that of the second image within a block with accuracy. 
     In the above configuration, the interpolation means may interpolate the block of the image having the luminance having a smaller than the luminance of the block to be compared with for every given frames of each of the first image and the second image. 
     This simplifies the process. 
     A display device according to the present invention includes: a display that displays a first image and a second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions; and the display control device according to any one of claims  1  to  9 . 
     A display control method according to the present invention includes: a step that compares a luminance of a first image with a luminance of a second image in units of pixel; a step that that interpolates a pixel value, having a luminance smaller than an attention pixel of at least one of the first image and the second image, in said at least one of the first image and the second image, when a difference in luminance between an attention pixel of the first image and an attention pixel of the second image is equal to or greater than a first threshold value; and a step that displays the first image and the second image on a common display portion such that the first image and the second image are respectively visible from different viewing directions. 
     Effects of the Invention 
     The present invention reduces the crosstalk of the images and improves the visibility of the images. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a basic configuration of a display device in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view illustrating an example in which the display device is applied to a vehicle; 
         FIG. 3  is a functional block diagram illustrating a configuration of the display device; 
         FIG. 4  is a functional block diagram illustrating a configuration of a controller; 
         FIG. 5  is a functional block diagram illustrating a configuration of first and second image quality adjusting circuits; 
         FIG. 6  is a view illustrating a cross-sectional configuration of a display  100 ; 
         FIG. 7  is a front view of a liquid crystal panel; 
         FIG. 8  is a circuit diagram of a TFT substrate; 
         FIG. 9  is a functional block diagram illustrating a configuration of an image outputting portion; 
         FIG. 10  is a view illustrating a first circuit configuration determining whether or not a luminance of an attention pixel of a first image data is similar to that of an attention pixel of a second image; 
         FIG. 11  is a flowchart illustrating a process sequence of the controller; 
         FIG. 12  is an explanatory view of a method for comparing the first image data and the second image data in units of pixel; 
         FIG. 13  is a view illustrating the state where an interpolation pixel is interpolated alternately in a passenger&#39;s seat side image and a driver&#39;s side image; 
         FIG. 14  is a view illustrating a second circuit configuration determining whether or not the luminance of the attention pixel of the first image data is similar to that of the attention pixel of the second image; 
         FIG. 15  is a flowchart illustrating a process sequence of the controller; 
         FIG. 16  is a view illustrating a third circuit configuration determining whether or not the luminance of the attention pixel of the first image data is similar to that of the attention pixel of the second image; 
         FIG. 17  is a flowchart illustrating a process sequence of the controller; 
         FIG. 18  is a view illustrating a fourth circuit configuration determining whether or not the luminance of the attention pixel of the first image data is similar to that of the attention pixel of the second image; 
         FIG. 19  is an explanatory view of a method for comparing the first image data and the second image data in units of pixel; 
         FIGS. 20A and 20B  are explanatory views of a method for comparing the first image data and the second image data in units of pixel; 
         FIG. 21  is a view illustrating one flame of image data is divided in units of block each being composed of N dot ′ M line, and explaining a method for controlling an interpolation of an interpolation image in units of block; and 
         FIG. 22  is an explanatory view of a method for interpolating the interpolation image for every given frames. 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     A description will be given of preferred embodiments with reference to the accompanying drawings. 
     First Embodiment  
     In the following, a description will be given of preferred embodiments with reference to the accompanying drawings. 
       FIG. 1  is a view illustrating a basic configuration of a multi-view display device in accordance with an embodiment of the present invention. 
     Referring now to  FIG. 1 , the multi-view display apparatus includes a display controller  10  that serves as a display control device and a display  100  that serves as a display portion. 
     To the display controller  10 , image data (image signal) DT 1  is supplied from a first image source  300 A, and image data (image signal) DT 2  is also supplied from a second image source  300 B. Then, the display controller  10  inputs these image data and outputs image data (image signal) ADT, which is composed of the first image data DT 1  and the second image data DT 2 , to the common display  100 . The configuration of the display controller  10  will be described later in detail. 
     The first image source  300 A and the second image source  300 B are respectively composed of a camera, a TV receiver, a DVD reproducing portion, a HD reproducing portion, a navigation portion, and the like, as will be described later. 
     The display  100  has a liquid crystal panel, a backlight, a parallax barrier, and the like (as will be described later in detail). The display  100  displays the first image IM 1  based on the first image data to be visible by an observer OBR from the right side. Also, the display  100  displays the second image IM 2  based on the second image data to be visible by an observer OBL from the left side. The first image data DT 1  and the second image data DT 2  are displayed on the common display. The configuration of the display  100  will also be described later in detail. 
       FIG. 2  is a perspective view illustrating an example in which the display controller  10  and the display  100  are applied to a vehicle. 
     Referring to  FIG. 2 , the display  100  is arranged between a driver&#39;s seat DS and a front passenger&#39;s seat AS in a dashboard area of the vehicle. In addition, the display  100  is provided with an operating portion  150  so as to manually operate the display controller  10 . 
     According to an exemplary embodiment shown in  FIG. 2 , a passenger who sits on the driver&#39;s seat DS corresponds to the above-described observer OBR, and another passenger who sits on the front passenger&#39;s seat AS corresponds to the above-described observer OBL. Those passengers are able to simultaneously watch the first image IM 1  and the second image IM 2 , which are respectively different, and which are bing displayed on the screen on the display  100  from the driver&#39;s seat DS and from the front passenger&#39;s seat AS. 
       FIG. 3  through  FIG. 9  illustrate specific configurations of the display apparatus in accordance with the exemplary embodiment of the present invention.  FIG. 3  is a functional block diagram of the display controller  10  and the display  100 .  FIG. 4  is a functional block diagram showing a configuration of the controller illustrated in  FIG. 3 .  FIG. 5  is a functional block diagram of first and second image quality adjusting circuits illustrated in  FIG. 3 .  FIG. 6  is a view illustrating a cross-sectional configuration and effects of a liquid crystal panel.  FIG. 7  is a front view of the liquid crystal panel illustrated in  FIG. 3 .  FIG. 8  is a circuit diagram of a TFT substrate.  FIG. 9  is a view showing a configuration of an image outputting portion  70  illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , the display controller  10  includes a controller  20 , a distribution circuit  30 , a first image quality adjusting circuit  50 A, a second image quality adjusting circuit  50 B, the image outputting portion  70 , and the like. 
     Referring now to  FIG. 4 , the controller  20  includes a CPU  21 , an interface  22 , a ROM  23  serving as a program storing portion, a RAM  24  serving as a data storing portion, and the like. The controller  20  controls the multi-view display apparatus according to a program stored in the ROM  23  in a comprehensive manner. The specific control by the controller  20  will also be described later in detail. 
     The controller  20  is connected to a camera  310 , a CD/MD (compact disc/mini disc) reproducing portion  320 , a radio receiver  330 , a TV receiver  340 , a DVD (digital versatile disc) reproducing portion  350 , a HD (hard disc) reproducing portion  360 , a navigation portion  370 , and the like, which are mounted on a vehicle and respectively serve as supply sources supplying images and sounds, as illustrated in  FIG. 3 . The controller  20  sends and receives data and controls the afore-described components. 
     The camera  310  captures images of surroundings and the like of the vehicle. The CD/MD reproducing portion  320  reproduces music or images. The radio receiver  330  receives radio waves via an antenna. The TV receiver  340  receives TV waves via an antenna through a selector  341 . The DVD reproducing portion  350  reproduces music information and images in a DVD. The HD reproducing portion  360  reproduces images and music information stored in a HD. The navigation portion  370  outputs maps or route guide images on the basis of road information received by a VICS (Vehicle Information and Communication System) information receiver  371  and geographic information received by a GPS (Global Positioning System) information receiver  372 . 
     Additionally, the controller  20  is also connected to a memory  140 , the operating portion  150 , a remote control send and receive portion  170 , a brightness detecting sensor  190 , a passenger detecting sensor  200 , and the like. The controller  20  enables various controls on the basis of various kinds of data obtained from the afore-mentioned components. 
     The memory  140  stores various kinds of data. The operating portion  150  is provided for operating the display apparatus. The remote control send and receive portion  170  sends and receives infrared signals or wireless signals between a remote controller  171  provided for controlling the display apparatus remotely. The brightness detecting sensor  190  is composed of a light switch or a light sensor to detect the brightness inside the vehicle. The passenger detecting sensor  200  is composed of a pressure-sensitive sensor or the like on the driver&#39;s seat or the front passenger&#39;s seat to detect a passenger in the vehicle. 
     The distribution circuit  30  distributes sound data and image data supplied from the above-described camera  310 , the CD/MD reproducing portion  320 , the radio receiver  330 , the TV receiver  340 , the DVD reproducing portion  350 , the HD reproducing portion  360 , the navigation portion  370 , and the like, to the first image quality adjusting circuit  50 A or the second image quality adjusting circuit  50 B, according to a control instruction issued by the controller  20 . 
     A sound adjusting circuit  60  adjusts the sound data supplied from the distribution circuit  30  to output to a speaker  61 . 
     Each of the first image quality adjusting circuit  50 A and the second image quality adjusting circuit  50 B, by reference to  FIG. 5 , includes a contrast adjusting portion  51 , a luminance adjusting portion  52 , a color tone adjusting portion  53 , a gamma value adjusting portion  54 , and the like. Each of the first image quality adjusting circuit  50 A and the second image quality adjusting circuit  50 B respectively adjusts the image qualities (contrast, luimnance, color tone, and gamma value) of the image qualities of the first image data and the second image data (image signal), in response to the control instruction issued by the controller  20 . 
     The display  100  includes the liquid crystal panel  110 , a backlight  120 , a touch panel  130 , and the like, as illustrated in  FIG. 3 . The backlight  120  sheds illuminated lights from the backside of the liquid crystal panel  110 . The touch panel  130  is provided for inputting a signal to operate the multi-view display apparatus. Here, the touch panel  130  is not shown, yet is formed in a shape of transparent sheet and adhered to the front surface of the liquid crystal panel  110 . 
     Referring now to  FIG. 6 , the liquid crystal panel  110  has a known structure. Sequentially from the backlight  120 , there are provided a first deflecting plate  111 , a thin film transistor (TFT) substrate  112 , a liquid crystal layer  113 , a color filter substrate  114  having pixels for three primary colors of RGB, a parallax barrier  115 , a glass plate  116 , a second deflecting plate  117 , and the like. 
     The above-described liquid crystal panel  110  has a display screen in which, for example, 800 pixels are arranged in a horizontal direction and 480 pixels in a vertical direction, as illustrated in  FIG. 7  and  FIG. 8 . Also, left-hand side display pixels  118  and right-hand side display pixels  119  are alternately arranged in a horizontal direction of the display screen. 
     The parallax barrier  115  is formed in a stripe-shaped manner, and includes shielding portions and transmitting portions, as illustrated in  FIG. 7  and  FIG. 8 . The shielding portions are arranged between the left-hand side display pixels  118  and the right-hand side display pixels  119  that are adjacent to each other. By providing the parallax barrier  115  on the front surface of the color filter substrate  114 , only the lights going towards the left side selectively pass through the transmitting portions of the parallax barrier  115  among the illuminated lights that have passed through the left-hand side display pixels  118 . Also, only the lights going towards the right side selectively pass through the transmitting portions of the parallax barrier  115  among the illuminated lights that have passed through the right-hand side display pixels  119 . As illustrated in  FIG. 6 , this makes the first image data IM 1  visible from the right side (the driver&#39;s seat) of the liquid crystal panel  110 , and also makes the second image data IM 2  visible from the left side (the front passenger&#39;s side). 
     Here, a similar parallax barrier as disclosed in Japanese Patent Application Publication No. 10-123461 or Japanese Patent Application Publication No. 11-84131 may be employed for the parallax barrier  115 . 
     The TFT substrate  112 , by reference to  FIG. 8 , includes a data line drive circuit DR 1 , a scanning line drive circuit DR 2 , vertically arranged scanning lines SCL, horizontally arranged data lines DTL, TFT elements EL, pixel electrodes EP corresponding to the TFT elements EL, and the like, whereas each of the TFT elements EL is formed in each region where each of the scanning lines SCL and each of the data lines DTL are crossed. Sub pixels SBP are formed by regions surrounded by the scanning lines SCL and the data lines DTL. Also, the sub pixels SBP arranged along each of the data lines DTL are alternately assigned to the left-hand side display pixels  118  and the right-hand side display pixels  119 . 
     A drive timing of the data line drive circuit DR 1  is controlled by a liquid crystal panel driving unit  74 , as will be described later, to control a voltage applied to the pixel electrode EP. 
     A drive timing of the scanning line drive circuit DR 2  is controlled by the liquid crystal panel driving unit  74 , as will be described later, to selectively scan the TFT element EL. 
     The memory  140  may be formed with an electrically rewritable nonvolatile memory such as a flash memory or a volatile memory backed up with batteries, for example. The memory  140  stores necessary data for control operations to be performed by the controller  20 , and the like. 
     As illustrated in  FIG. 9 , the image output unit  70  includes frame memories  510 A and  510 B, auxiliary frame memories  520 A and  520 B, a liquid crystal panel driving unit  74 , switches SW 1  and SW 2 , and the like. 
     The first and second image data (image signals) DT 1  and DT 2  having the image quality adjusted by the first and second image quality adjusting circuits  50 A and  50 B are written in the frame memories  510 A and  510 B, respectively. The first and second image data DT 1  and DT 2  are image signals (video signals) from the TV reception unit  340 , the DVD reproduction unit  350 , the navigation unit  370 , or the like. 
     The interpolation image data SB 1  and SB 2  are written in the auxiliary frame memories  510 A and  510 B by the controller  20 . 
     The interpolation image data SB 1  and SB 2  are provided for displaying a black image on the display  100 , as will be described later. 
     The switch SW 1  selectively connects a movable contact point C 3  to fixed contact points C 1  and C 2 , in response to the synchronization signal SC outputted from the controller  20 . When the fixed contact point C 1  is connected to the movable contact point C 3 , the image data DT 1  held in the frame memory  510 A is output to the liquid crystal panel driving unit  74 . When the fixed contact point C 2  is connected to the movable contact point C 3 , the interpolation image data SB 1  held n the auxiliary frame memory  520 A is output to the liquid crystal panel driving unit  74 . 
     The switch SW 2  selectively connects the movable contact point C 3  to the contact points C 1  and C 2 , in response to the synchronization signal SC outputted from the controller  20 . When the fixed contact point C 1  is connected to the movable contact point C 3 , the image data DT 2  held in the frame memory  510 B is output to the liquid crystal panel driving unit  74 . 
     When the fixed contact point C 2  is connected to the movable contact point C 3 , the interpolation image data SB 2  held n the auxiliary frame memory  520 B is output to the liquid crystal panel driving unit  74 . 
     The liquid crystal panel driving unit  74  drives the liquid crystal panel  110  of the display  100 . The liquid crystal panel driving unit  74  drives the pixels of the liquid crystal panel  110  so as to display the images for the driver&#39;s seat (D seat) side, based on the image data held in the frame memory  510 A or the interpolation image data held in the auxiliary frame memory  520 A. Also, the liquid crystal panel driving unit  74  drives the pixels of the liquid crystal panel  110  so as to display the images for the front passenger&#39;s seat (P seat) side, based on the image data held in the frame memory  510 B or the interpolation image data held in the auxiliary frame memory  520 B. Additionally, a sorting process for sorting data to correspond to each pixel of the liquid crystal panel  110  is performed by the liquid crystal panel driving unit  74 . 
     Next, a description will be given of a circuit configuration that compares the luminance of the first image data DT 1  with that of the second image data DT 2  in units of pixels. 
     The circuit configuration illustrated in  FIG. 10  includes a differential circuit  600 , and a comparison circuit (which corresponds to comparison means according to the present invention)  610 , and compares the luminance of the first image data DT 1  with that of the second image data DT 2  in units of pixels. The comparison circuit  610  is outputted to the controller  20 . The controller (which corresponds to an interpolation unit according to the present invention)  20  switches between the switches SW 1  and SW 2 , in response to a comparison result of the comparison circuit  610 . 
     The differential circuit  600  calculates a difference between the luminance of the first image data DT 1  and that of the second image data DT 2 . The first image data DT 1  and the second image data DT 2  are inputted to the differential circuit  600 , and then the differential circuit  600  determines the difference in luminance between the image data DT 1  and the image data DT 2  on a pixel basis. 
     The differential circuit  600  creates each luminance value Y of the first image data DT 1  and that of the second image data DT 2  for every pixel, and then determines the difference of the luminance values Y. The luminance value of NTSC (National Television Standards Committee) is determined on the basis of the RGB (red, green, blue) signal by a following formula (1). 
         Y= 0.29′ R+ 0.6′ G+ 0.11′ B   (1) 
     The comparison circuit  610  compares the differential value calculated by the differential circuit  600  with the first threshold value, and then outputs a signal that indicates a comparison result to the controller  20 . The first threshold value is used as a threshold value for detecting that the attention pixel of the first image data DT 1  and that of the second image data DT 2  have a small difference in luminance. When the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is equal to or smaller than the first threshold value, the comparison circuit  610  outputs to the controller  20  a signal (hereinafter referred to as signal of no difference in luminance), indicating that the difference in luminance between both pixels is equal to or smaller than the first threshold value. In addition, when the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is greater than the first threshold value, the comparison circuit  610  outputs a signal (hereinafter referred to as signal of any difference in luminance), indicating that the difference in luminance between both pixels is greater than the first threshold value. 
     When the signal of no difference in luminance is outputted from the comparison circuit  610  to the controller  20 , the controller  20  controls the switches SW 1  and SW 2  illustrated in  FIGS. 9 and 10 , and causes the first image data DT 1  and the second image data DT 2  respectively stored in the frame memories  510 A and  510 B to be outputted to the liquid crystal panel driving unit  74 . 
     Additionally, when the signal of any difference in luminance is outputted from the comparison circuit  610  to the controller  20 , the controller  20  connects the fixed contact point C 1  of the switch SW 1  to the movable contact point C 3 , and also connects the fixed contact point C 2  of the switch SW 2  to the movable contact point C 3 . That is, the pixel value of the attention pixel read from the frame memory  510 A is outputted to the attention pixel of the first image data DT 1 , and the pixel value of the interpolation pixel read from the auxiliary frame memory  520 B is interpolated to the attention pixel of the second image data DT 2 . Further, the controller  20  connects the fixed contact point C 2  of the switch SW 1  to the movable contact point C 3 , and also connects the fixed contact point C 1  of the switch SW 2  to the movable contact point C 3 . That is, the pixel value of the attention pixel read from the frame memory  510 B is outputted to the attention pixel of the second image data DT 2 , and the pixel value of the interpolation pixel read from the auxiliary frame memory  520 A is interpolated to the attention pixel of the first image data DT 1 . 
     A description will be given of a process sequence of the controller  20  with reference to a flowchart as illustrated in  FIG. 11 . In addition, the interpolation pixel to be interpolated will be described as a black pixel in this flow chart. 
     When the signal of no difference in luminance is inputted to the controller  20 , the controller  20  determines that the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is equal to or smaller than the first threshold value (step S 1 /YES). 
     In this case, the controller  20  switches between the switches SW 1  and SW 2  to turn off the interpolation of the black pixel (step S 2 ). Since the difference in luminance between the first image data DT 1  and the second image data DT 2  is small, the black pixel is not interpolated, and then the pixel values of the first image data DT 1  and the second image data DT 2  are outputted without being changed. Also, the signal of any difference in luminance is inputted from the comparison circuit  610  to the controller  20 , the controller  20  determines that the difference in luminance between the attention pixels of the first image data DT 1  and the second image data DT 2  is greater than the first threshold value (step S 1 /No). In this case, the controller  20  alternately switches between the switches SW 1  and SW 2  to alternately interpolate the black pixel to the first image data DT 1  and the second image data DT 2 . The above mentioned processes are applied to all of the input pixels (step S 4 ). 
     Here, a description will be given of the processes of the differential circuit  600  and the comparison circuit  610  in detail with reference to  FIG. 12 . In addition, in the following description, the first image data DT 1  will be described as a driver&#39;s side image D that is visible from the driver&#39;s seat side, and the second image data DT 2  will be described as a passenger&#39;s seat side image P that is visible from the passenger&#39;s seat side. 
     At (a-1) illustrated in  FIG. 12 , the first image data DT 1  stored in the frame memory  510 A and the second image data DT 2  stored in the frame memory  510 B are arranged in units of pixel. The pixels D 1 , D 2 , D 3 , D 4 , . . . , are read from the frame memory  510 A in this order, as illustrated at (a-1) in  FIG. 12 , and are then outputted to the differential circuit  600 . Likewise, the pixels P 1 , P 2 , P 3 , P 4 , . . . , are read from the frame memory  510 B in this order, as illustrated at (a-1) in  FIG. 12 , and are then outputted to the differential circuit  600 . 
     The differential circuit  600  determines the difference in luminance between the pixel read from the frame memory  510 A and the pixel read from the frame memory  510 B. For example, when an attention is paid to D 3  and P 3  illustrated in  FIG. 12 , the differential circuit  600  determines (D 3 -P 3 ) as a differential value in luminance, and then outputs it to the comparison circuit  610 . The comparison circuit  610  compares (D 3 -P 3 ) with the first threshold value. When the difference in luminance is equal to or smaller than the first threshold value, the comparison circuit  610  outputs the signal of no difference in luminance, indicating that the difference in luminance is equal to or smaller than the first threshold value, to the controller  20 . Additionally, when the difference in luminance is greater than the first threshold value, the comparison circuit  610  outputs to the controller  20  the signal of any difference in luminance, indicating that the difference in luminance is greater than the first threshold value. 
     When the signal of no difference in luminance is inputted from the comparison circuit  610  to the controller  20 , the controller  20  controls the switches SW 1  and SW 2  to alternately interpolate the interpolation pixel stored in the auxiliary frame memory  520 A to the driver&#39;s side image D and interpolate the interpolation pixel stored in the auxiliary frame memory  520 B to the front passenger&#39;s seat side image P. In the example illustrated in  FIG. 12 , the pixel S 3  is read, as the interpolation pixel of the driver&#39;s side image D 3  and the front passenger&#39;s seat side image P 3 , from the auxiliary frame memories  520 A and  520 B. A series of pixels to be outputted as the front passenger&#39;s seat side image P is illustrated at a-4 in  FIG. 12 . A series of pixels to be outputted as the drive side image D is illustrated at a-5 in  FIG. 12 . As illustrated in  FIG. 12 , the controller  20  switches the connections of the switches SW 1  and SW 2  to alternately output the interpolation pixel S 3  to the driver&#39;s side image D and the front passenger&#39;s seat side image P. 
       FIG. 13  shows an example of the image displayed on the display  100  by the above-mentioned processes. In the example shown in  FIG. 13 , to reduce the large difference in luminance between the edge areas of the first image data DT 1  and the second image data DT 2 , the interpolation pixel is interpolated alternately in the edge areas of the first image data DT 1  and the second image data DT 2 . 
     In the above-mentioned present embodiment, the luminance of the first image data DT 1  is compared with that of the second image data DT 2  in units of pixels, and the pixel having reduced luminance is interpolated at the time when the difference in luminance is equal to or greater than the first threshold value, thereby reducing the luminance. This reduces the crosstalk of the images and improves the visibility of the images. 
     [First Variation] 
     A circuit, which compares the luminance of the first image data DT 1  with that of the second image data DT 2  in units of pixels and which controls the image data to be outputted to the liquid crystal panel driving unit  74 , may have a configuration illustrated in  FIG. 14 . 
     The circuit configuration illustrated in  FIG. 14  includes AND gates (corresponding to interpolation means according to the present invention)  621  and  622 , and low-pass filters (hereinafter referred to as LPFs)  623  and  624 , instead of the auxiliary frame memories  520 A and  520 B illustrated in  FIG. 9 . In addition, a threshold value, which is inputted to a comparison circuit (corresponding to comparison means according to the present invention)  620 , is modified to a second threshold value from the first threshold vale. 
     The second threshold value, which is inputted to the comparison circuit  620 , is provided for detecting that there is a large difference in luminance between the first image data DT 1  and the second image data DT 2 . When the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is greater than the second threshold value, the comparison circuit  620  outputs to the controller  20  the signal of any difference in luminance, indicating that there is a large difference in luminance of the attention pixels. This signal of any difference in luminance is also outputted to the AND gates  621  and  622  illustrated in  FIG. 14 . Additionally, when the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is equal to or smaller than the second threshold value, the comparison circuit  620  outputs to the controller  20  the signal of no difference in luminance, indicating that there is a small difference in luminance of the attention pixels. 
     The AND gate  621  is supplied with a signal (signal of no difference in luminance or signal of any difference in luminance), which indicates the comparison result, from the comparison circuit  620 , and a signal (hereinafter referred to as first signal), which indicates that the luminance of the attention pixel of the first image data DT 1  is equal to or greater than that of the attention pixel of the second image data DT 2 . The first signal is outputted from the controller  20  to the AND gate  621 . When the signal of any difference in luminance is inputted to the AND gate  621  from the comparison circuit  620  and the first signal is inputted to the AND gate  621  from the controller  20 , the AND gate  621  switches the switch SW 1  to output the signal from the LPF  623  to the liquid crystal panel driving unit  74 . 
     The luminance of the first image data DT 1  passing through the LPF  623  is a lowered signal. 
     Also, the signal (signal of no difference in luminance or signal of any difference in luminance), which indicates the comparison result, is inputted to the AND gate  622  from the comparison circuit  620 . A signal (hereinafter referred to as second signal), which indicates that the luminance of the attention pixel of the first image data DT 1  is smaller than that of the attention pixel of the second image data DT 2 , is inputted to the comparison circuit  620 . The second signal is outputted from the controller  20  to the AND gate  622 . When the signal of any difference in luminance is inputted to the AND gate  622  from the comparison circuit  620  and the second signal is inputted to the AND gate  622  from the controller  20 , the AND gate  622  switches the switch SW 2  to output the signal from the LPF  624  to the liquid crystal panel driving unit  74 . 
     The luminance of the second image data DT 2  passing through the LPF  623  is also a lowered signal. 
     When the output of the LPF  623  or  624  is selected, the liquid crystal panel driving unit  74  alternately inserts the output from the LPF  623  to the first image data DT 1  and inserts the output from the LPF  624  to the second image data DT 2 , the first image data DT 1  and the second image data DT 2  being outputted to the liquid crystal panel driving unit  74 . 
     A description will be given of a process sequence the circuit illustrated in  FIG. 14  with reference to a flowchart illustrated in  FIG. 15 . 
     When the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is greater than the second threshold value (step S 10 /YES), the comparison circuit  620  outputs the signal of any difference in luminance, indicating that the difference in luminance is greater than the second threshold value, to the controller  20 , and to the AND gates  621  and  622 . 
     When the luminance of the attention pixel of the first image data DT 1  is equal to or greater than that of the attention pixel of the second image data DT 2  (step S 12 /YES), the first signal is outputted to the AND gate  621  by the controller  20 . When the first signal and the signal of any difference in luminance are inputted to the AND gate  621 , the AND gate  621  outputs a high-level signal for switching the switch SW 1 . By the output signal from the AND gate  621 , the switch SW 1  is switched, so the output of the LPF  623  is selected (step S 13 ). The output of the LPF  623  is inputted to the liquid crystal panel driving unit  74 . 
     When the luminance of the attention pixel of the first image data DT 1  is smaller than that of the attention pixel of the second image data DT 2  (step S 12 /NO), the second signal is outputted to the AND gate  622  from the controller  20 . When the second signal and the signal of any difference in luminance are inputted to the AND gate  622 , the AND gate  622  outputs a high-level signal for switching the switch SW 2 . By the output signal from the AND gate  622 , the switch SW 2  is switched, so the output of the LPF  624  is selected (step S 14 ). The output of the LPF  624  is inputted to the liquid crystal panel driving unit  74 . 
     When the signal having a small luminance and passing through the LPF  623  or LPF  624  is inputted to the liquid crystal panel driving unit  74 , the liquid crystal panel driving unit  74  switches its output to alternately insert the signal to the first image data DT 1  and the second image data DT 2 . 
     Also, when the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is equal to or smaller than the second threshold value (step S 10 /NO), the comparison circuit  620  outputs the signal of no difference in luminance to the controller  20 . By outputting the signal of no difference in luminance to the AND gates  621  and  622 , the outputs of the AND gates  621  and  622  are switched to low levels. Thus, the switches SW 1  and SW 2  are connected to the fixed contact point C 1  side (step S 11 ), so that the attention pixel of the first image data DT 1  and that of the second image data DT 2  are directly outputted to the liquid crystal panel driving unit  74 . 
     [Second Variation] 
     A circuit configuration, which compares the luminance of the first image data DT 1  with that of the second image data DT 2  in units of pixels and which controls the image data to be outputted to the liquid crystal panel driving unit  74 , may have a configuration illustrated in  FIG. 16 . 
     The circuit configuration illustrated in  FIG. 16  includes a comparator (corresponding to an interpolation unit according to the present invention)  630 , instead of the comparison circuit  610  illustrated in  FIG. 10 . A third threshold value and a fourth threshold value are inputted to the comparator  630 , in addition to the differential value of the luminance calculated by the differential circuit  600 . The forth threshold value is set to be greater than the third threshold value (third threshold value&lt;forth threshold value). In addition, the forth threshold value corresponds to a second threshold value recited in claims, and the third threshold value corresponds to a third threshold value recited in claims. 
     When the differential value calculated by the differential circuit  600  is equal to or greater than the third threshold value and is smaller than the forth threshold value, the comparator  630  outputs a signal (hereinafter referred to as third signal), indicating that the difference in luminance is equal to or greater than the third threshold value and is smaller than the forth threshold value, to the controller  20 . 
     When the third signal is inputted from the comparator  630  to the controller (corresponding to an interpolation unit according to the present invention)  20 , the controller  20  reduces the luminance of the corresponding pixel on the basis of this signal. 
     When the differential value calculated by the differential circuit  600  is smaller than the third threshold value, the comparator  630  outputs a signal (hereinafter referred to as fourth signal), indicating that the difference in luminance is smaller than the third threshold value, to the controller  20 . When the fourth signal is inputted from the comparator  630  to the controller  20 , the controller  20  determines that there is no difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2 , and then prohibits the interpolation of a black pixel. 
     When the differential value calculated by the differential circuit  600  is greater than the fourth threshold value, the comparator  630  outputs a signal (hereinafter referred to as fifth signal), indicating that the difference in luminance is greater than the fourth threshold value, to the controller  20 . When the fifth signal is inputted to the comparator  630 , the controller  20  determines that the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2 , and then outputs a signal for permitting the black pixel to be interpolated. Additionally, the third threshold value may be set to be identical with the first threshold value. Likewise, the fourth threshold value may be set to be identical with the second threshold value. 
     A description will be given of a process sequence of the controller  20  with reference to a flowchart illustrated in  FIG. 17 . 
     When the fourth signal, which indicates that the difference in luminance is smaller than the third threshold, is inputted from the comparator  630  to the controller  20  (step S 21 /YES), the controller  20  determines that the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2 , and then set to turn off the interpolation of the black pixel (step S 22 ). 
     When the third signal, which indicates that the differential value in luminance is equal to or greater than the third threshold value and is smaller than the forth threshold value, is inputted from the comparator  630  to the controller  20  (step S 23 /YES), the controller  20  reduces the luminance of the corresponding pixel on the basis of this signal (step S 24 ). 
     When the fifth signal, which indicates that the differential value in luminance is equal to or greater than the forth threshold value, is inputted from the comparator  630  to the controller  20  (step S 25 /YES), the controller  20  determines that the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2 , and then outputs a signal for permitting the black pixel to be interpolated (step S 26 ). 
     [Third Variation] 
     A circuit, which compares the luminance of the first image data DT 1  with that of the second image data DT 2  in units of pixels and which controls the image data to be outputted to the liquid crystal panel driving unit  74 , may have a configuration illustrated in  FIG. 18 . 
     The circuit configuration illustrated in  FIG. 18  directly outputs the differential value in luminance, which is calculated by the differential circuit  600  illustrated in  FIG. 10 , to the controller  20 . 
     The controller  20  controls the luminance of the attention pixel in response to the difference in luminance calculated by the differential circuit  600 . That is, the luminance of the attention pixel is reduced and a pixel more similar to the black pixel is interpolated, as the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is greater. When the difference in luminance between the attention pixel of the first image data DT 1  and that of the second image data DT 2  is small, the luminance of the attention pixel is not reduced and a pixel more similar to the white pixel is interpolated. 
     In the above description, the luminance of the attention pixel of the first image data DT 1  and that of the attention pixel of the second image data DT 2  are directly compared by calculating the difference in luminance between the attention pixels. In addition thereto, the comparison can be performed by methods illustrated in  FIGS. 19 and 20 . In the method illustrated in  FIG. 19 , the luminance of the attention pixel is compared with a luminance of an adjacent pixel, in addition to the comparison of the attention pixel of the first image data DT 1  and that of the second image data DT 2 . 
     A description will be given of a method for comparing the luminance in  FIG. 19 . First, an adding circuit not illustrated is provided in a former stage of the differential circuit  600 , and adds the pixel values of the adjacent pixels of the driver&#39;s side image D. That is, (D 1 +D 2 ), (D 2 +D 3 ), (D 3 +D 4 ), . . . , are determined by adding the pixel values of the adjacent pixels of the driver&#39;s side images D 1 , D 2 , D 3 , D 4 , . . . . Likewise, (P 1 +P 2 ), (P 2 +P 3 ), (P 3 +P 4 ), . . . , are determined by adding the pixel values of the adjacent pixels of the front passenger&#39;s seat side images P 1 , D 2 , P 3 , P 4 , . . . . 
     The differential circuit  600  determines the difference between the driver&#39;s side image and the front passenger&#39;s seat side image, which are added by the adding circuit. In the example shown in  FIG. 19 , the difference between (D 1 +D 2 ) and (P 1 +P 2 ), the difference between (D 2 +D 3 ) and (P 2 +P 3 ), and the like are determined (referring to (a-2) in  FIG. 19 ). The comparison circuit  610  determines whether or not the interpolation pixel is interpolated to the attention pixel, on the basis of the calculated differential value of the luminance. (a-3) in  FIG. 19  illustrates the state where the interpolation pixels (S 1 , S 2 , S 3 , S 4 , . . . ) are selected in response to the comparison result of the comparison circuit  610 . Further, (a-4, a-5) illustrates the state where the difference between the driver&#39;s side image D and the front passenger&#39;s seat side image P is greater than the threshold value is continuously generated, and where the interpolation pixel is alternately interpolated in the driver&#39;s side image D and the front passenger&#39;s seat side image P. 
     Also, the driver&#39;s side image D and the front passenger&#39;s seat side image P may be individually processed. In the example shown in  FIGS. 20A and 20B , regarding the process of the front passenger&#39;s seat side image P, the additional values (P 1 +P 2 ), (P 2 +P 3 ), . . . are determined by adding the adjacent pixels of the front passenger&#39;s seat side images P 1 , P 2 , P 3 , . . . as illustrated at (a-2) in  FIG. 20A . Pixel values (D 1 ′ 2 ), (D 2 ′ 2 ), . . . are determined by doubling each of the driver&#39;s seat side images D 1 , D 2 , D 3  . . . . Next, the differential circuit  600  determines the difference between these pixel values. That is, the difference in luminance between (P 1 +P 2 ) and (D 1 ′ 2 ), the difference in luminance between (P 2 +P 3 ) and (D 2 ′ 2 ), and the like are determined as illustrated at (a-2) in  FIG. 20A . The comparison circuit  610  determines whether or not the interpolation pixel is interpolated to the attention pixel on the basis of the calculated differential value of the luminance. (a-3) in  FIG. 20A  illustrates the state where the interpolation pixels (S 1 , S 2 , S 3 , S 4 , . . . ) are selected in response to the comparison result of the comparison circuit  610 . When the interpolation pixel is selected, the interpolation pixel is interpolated in the front passenger&#39;s seat side image P as illustrated at (a-4) in  FIG. 20A . 
     Likewise, in the process for the driver&#39;s side image D, the additional values (D 1 +D 2 ), (D 2 +D 3 ), . . . are determined by adding the adjacent pixels of the driver&#39;s side images D 1 , D 2 , D 3 , as illustrated at (b-2) in  FIG. 20A . Pixel values (P 1 ′ 2 ), (P 2 ′ 2 ), . . . are determined by doubling each of the front passenger&#39;s seat side images P 1 , P 2 , P 3  . . . . Then, the differential circuit  600  determines the differences between these pixel values, and the comparison circuit  610  determines whether or not the interpolation pixels (T 1 , T 2 , T 3 , T 4  . . . ) are interpolated in the attention pixel. 
       FIG. 20B  shows the example where a supplementary image is displayed as the front passenger seat image at the time of displaying the driver&#39;s side image and where the supplementary image is displayed as the driver&#39;s side image at the time of displaying the front passenger&#39;s seat side image. 
     Further, there are various methods for calculating the luminance to be compared between the image data, in addition to the above-mentioned embodiments. For example, a difference between an R signal of the first image data DT 1  and that of the second image data DT 2 , a difference between a G signal of the first image data DT 1  and that of the second image data DT 2 , a difference between a B signal of the first image data DT 1  and that of the second image data DT 2 , may be determined on a pixel basis. An average value of these differences may be determined as the difference in luminance between the attention pixels. 
     Alternately, the highest luminance among the R, G, and B signals of the first image data DT 1 , and the highest luminance among the R, G, and B signals of the second image data DT 2 , may be determined. The difference between the both may be determined on a pixel basis. 
     Second Embodiment  
     In the above-mentioned first embodiment, the differential value between the first image data DT 1  and the second image data DT 2  are determined on a pixel basis, and this differential value is compared with the threshold value. 
     In the present embodiment, the one flame of image data is divided in units of block each being composed of N (dot) ′ M (line) (N and M are any natural numbers), as illustrated in  FIG. 21 . The luminance values of the first image data DT 1  and that of the second image data DT 2  are compared in units of the divided block. For example, the difference in luminance between the first image data DT 1  and the second image data DT 2  is determined in units of pixel, so the average value within one block is determined on the basis of the determined difference in luminance. The interpolation data, which is interpolated to the first image data DT 1  and the second image data DT 2 , is controlled on the basis of this average value. 
     Also, the pixel having the highest luminance in each of the first image data DT 1  and the second image data DT 2  within one block may be determined, and then the interpolation data, which is interpolated in the first image data DT 1  and the second image data DT 2 , may be controlled based on the difference in luminance of these pixels. 
     In this way, in the present embodiment, the first image data DT 1  and the second image data DT 2  are compensated to reduce the difference in luminance therebetween. This reduces the crosstalk of images and improves the visibility thereof. Moreover, the compensation is performed in units of block, thereby simplifying the process. 
     Third Embodiment 
     In the first and second embodiments, the interpolation of the interpolation data is controlled in all the frame of the image data. In the present embodiment, the frame to be processed by way of the first or second embodiment is selected, as illustrated in  FIG. 22 , and then the interpolation date is controlled for every a few frames. 
     The interpolation of the interpolation data may be controlled in units of pixel, as described in the first embodiment, or in units of block each being composed of N (dot) ′ M (line), as described in the second embodiment. Such control also ensures the same effects of the first and second embodiments. 
     The present invention is not limited to the above-mentioned embodiment, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.