Abstract:
An image display device includes the following elements: a display panel that has a plurality of pixels arranged in a predetermined first direction and in a second direction intersecting with the first direction; a light source that emits light to the display panel; a polarization axis controller that separates the light emitted from the light source into light with a first polarization axis and light with a second polarization axis different from the first polarization axis, the polarization axis controller being disposed between the display panel and the light source; and an optical element that directs the light emitted from the light source in a direction substantially orthogonal to the first direction, the optical element being disposed between the display panel and the polarization axis controller. The polarization axis controller includes the following elements: a first substrate; a second substrate; a liquid crystal layer held between the first substrate and the second substrate; a plurality of first electrodes disposed on the first substrate so as to extend in the first direction, the plurality of first electrodes being arranged at a predetermined interval in the second direction; and a plurality of second electrodes disposed on the second substrate so as to extend in the first direction, the plurality of second electrodes being arranged at an interval twice the predetermined interval in the second direction. The plurality of second electrodes is disposed so as to overlap at least part of the adjacent first electrodes.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to image display devices and electronic apparatuses, and more particularly to an image display device provided with a polarization axis controller and to an electronic apparatus.  
         [0003]     2. Related Art  
         [0004]     One known method for an image display device displaying a three-dimensional stereo image is a system employed in a three-dimensional image display device disclosed in Japanese Patent No. 2,857,429.  
         [0005]     In the three-dimensional image display device disclosed in Japanese Patent No. 2,857,429, an electronic parallax barrier disposed on a viewer side of an image display surface is controlled by a controller, such as a microcomputer, thereby forming apertures and light-blocking portions of the electronic parallax barrier so that an image for the left eye enters the left eye of the viewer and an image for the right eye enters the right eye of the viewer.  
         [0006]     However, since the electronic parallax barrier is disposed on the viewer side of the image display surface of the three-dimensional image display device disclosed in Japanese Patent No. 2,857,429, part of light emitted from the image display surface is blocked by the light-blocking portions of the electronic parallax barrier. As a result, the luminance of an image viewed by the viewer is reduced, and the image seems dark to the viewer.  
         [0007]     A known dual-screen display device is available for providing different images to viewers at different viewing positions by disposing a barrier having slit apertures and light-blocking portions on a viewer side of a display panel. This type of display device is disadvantageous in that part of light emitted from the display panel is blocked by the barrier, and, as a result, an image seems dark.  
       SUMMARY  
       [0008]     An advantage of some aspects of the invention is that it provides an image display device capable of displaying a three-dimensional image and functioning as a dual-screen display without reducing the luminance of an image viewed by viewers.  
         [0009]     According to an aspect of the invention, an image display device includes the following elements: a display panel that has a plurality of pixels arranged in a predetermined first direction and in a second direction intersecting with the first direction; a light source that emits light to the display panel; a polarization axis controller that separates the light emitted from the light source into light with a first polarization axis and light with a second polarization axis different from the first polarization axis, the polarization axis controller being disposed between the display panel and the light source; and an optical element that directs the light emitted from the light source in a direction substantially orthogonal to the first direction, the optical element being disposed between the display panel and the polarization axis controller. The polarization axis controller includes the following elements: a first substrate; a second substrate; a liquid crystal layer held between the first substrate and the second substrate; a plurality of first electrodes disposed on the first substrate so as to extend in the first direction, the plurality of first electrodes being arranged at a predetermined interval in the second direction; and a plurality of second electrodes disposed on the second substrate so as to extend in the first direction, the plurality of second electrodes being arranged at an interval twice the predetermined interval in the second direction. The plurality of second electrodes is disposed so as to overlap at least part of the adjacent first electrodes.  
         [0010]     With the structure of the aspect of the invention, part of light emitted from the display panel is not blocked by a barrier, and hence the luminance of an image viewed by viewers is not reduced. By controlling the state in which voltages are applied to the plurality of first electrodes and the plurality of second electrodes of the polarization axis controller, the length in the second direction of first and second polarization-controlled areas can be controlled. Accordingly, the direction in which light is directed can be switched using the optical element, and a display mode can be switched between a three-dimensional image display mode and a dual-screen display mode.  
         [0011]     It is preferable that the plurality of first electrodes be a plurality of strip electrodes of a pair of comb-like electrodes having a pair of connecting portions disposed along an outer periphery of the first substrate and the plurality of strip electrodes extending alternately from the pair of connecting portions inward of the first substrate, and that the plurality of second electrodes be a plurality of strip electrodes of a pair of comb-like electrodes having a pair of connecting portions disposed along an outer periphery of the second substrate and the plurality of strip electrodes extending alternately from the pair of connecting portions inward of the second substrate.  
         [0012]     With this structure, two electrodes to which different voltages are applied can be fabricated using a single electrically-conductive layer on each substrate, and hence a polarization-controlled liquid crystal panel can be easily fabricated.  
         [0013]     It is also preferable that the image display device further include a controller that switches an image display mode between a dual-screen display mode and a three-dimensional image display mode by controlling voltages applied to the plurality of first electrodes and the plurality of second electrodes.  
         [0014]     In this case, in the dual-screen display mode, the controller preferably applies voltages to the plurality of second electrodes so that the adjacent electrodes have opposite phases, and, to the plurality of first electrodes, preferably applies a voltage having the same phase as one of the voltages applied to the plurality of second electrodes. In the three-dimensional image display mode, the controller preferably applies voltages to the plurality of first electrodes so that the adjacent electrodes have opposite phases, and, to the plurality of second electrodes, preferably applies a voltage having the same phase as one of the voltages applied to the plurality of first electrodes.  
         [0015]     With this structure, the controller can be constructed using a combination of a simple known electrical circuit, and hence the controller can be easily fabricated.  
         [0016]     In this case, it is preferable that the controller apply the voltages to the plurality of first electrodes so that the adjacent electrodes have opposite phases and, to the second electrodes, apply a voltage with a period half that of the voltages applied to the plurality of first electrodes, thereby switching the image display mode to a two-dimensional image display mode.  
         [0017]     With this structure, the image display device capable of displaying a fine two-dimensional image can be realized.  
         [0018]     It is also preferable that the controller apply the voltages to the plurality of second electrodes so that the adjacent electrodes have opposite phases, and, to the plurality of first electrodes, apply a voltage having the same phase as the other voltage applied to the plurality of second electrodes, thereby switching the image display mode to a second dual-screen display mode.  
         [0019]     With this structure, images provided to viewers at different viewing positions can be switched without switching the positions at which the images are displayed on the display panel. Therefore, no image processing is necessary therefor, and no delay occurs in displaying the images when the directions in which the images are provided are switched.  
         [0020]     According to another aspect of the invention, an electronic apparatus includes the above-described image display device.  
         [0021]     With the structure of the aspect of the invention, a three-dimensional image with a high luminance can be displayed, while a dual-screen display can be realized. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements, and wherein:  
         [0023]      FIG. 1  is an exploded perspective view of an image display device;  
         [0024]      FIG. 2  is a view of a display panel viewed from the top by viewers for describing the principle of the image display device;  
         [0025]      FIG. 3  is a partly enlarged view of a polarization-controlled liquid crystal panel;  
         [0026]      FIG. 4  is an exploded perspective view of the polarization-controlled liquid crystal panel;  
         [0027]      FIG. 5  is a plan view of the polarization-controlled liquid crystal panel;  
         [0028]      FIG. 6  is a sectional view of the polarization-controlled liquid crystal panel taken along the line VI-VI of  FIG. 5 ;  
         [0029]      FIG. 7  is an electrical circuit diagram of a control circuit;  
         [0030]      FIGS. 8A  to  8 C are timing charts for describing voltages output from output ends;  
         [0031]      FIG. 9  is a view of the display panel viewed from the side by the viewers for describing the principle of the image display device;  
         [0032]      FIG. 10  is an exploded perspective view of the image display device for describing the principle of the image display device;  
         [0033]      FIG. 11  is a diagram for describing areas of the display panel viewed by the viewers in a dual-screen display mode of the image display device;  
         [0034]      FIG. 12  is a view of the display panel viewed from the top by the viewers for describing the principle of displaying a three-dimensional image by the image display device;  
         [0035]      FIG. 13  is an exploded perspective view of the image display device for describing the principle of displaying a three-dimensional image by the image display device;  
         [0036]      FIG. 14  is a diagram for describing areas of the display panel viewed by the viewers in a three-dimensional image display mode of the image display device;  
         [0037]      FIG. 15  is a diagram showing the polarization-controlled liquid crystal panel, a retardation film, and the display panel in a two-dimensional image display mode of the image display device;  
         [0038]      FIG. 16  is a diagram for describing areas of the display panel viewed by the viewers in the two-dimensional image display mode of the image display device;  
         [0039]      FIG. 17  is a perspective view showing the structure of a cellular phone;  
         [0040]      FIG. 18  is an electrical circuit diagram of a control circuit according to a second embodiment; and  
         [0041]      FIGS. 19A  to  19 D are timing charts for describing voltages output from output ends according to the second embodiment. 
     
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0042]     A first embodiment of the invention will be described with reference to FIGS.  1  to  17 .  
         [0043]     An image display device  1  of the first embodiment has three image display modes, namely, a dual-screen display mode in which different images are provided to viewers  10  and  20  residing at different viewing positions, a three-dimensional image display mode in which a three-dimensional image is provided to the viewers  10  and  20 , and a two-dimensional image display mode in which one and the same two-dimensional image is provided to the viewers  10  and  20 . By switching among these image display modes, the image display device  1  can provide images in various modes.  
         [0044]     The structure of the image display device  1  of the first embodiment will be described.  FIG. 1  is an exploded perspective view of the image display device of the first embodiment.  FIG. 2  is a view of a display panel viewed from the top by the viewers for describing the principle of the image display device of the first embodiment shown in  FIG. 1 .  FIG. 3  is a partly enlarged view of a polarization-controlled liquid crystal panel of the image display device shown in  FIG. 1 . The image display device  1  includes, as shown in  FIGS. 1 and 2 , a display panel  2  for displaying an image, polarization plates  3  and  4  disposed so as to have the display panel  2  therebetween, a backlight  5  for irradiating the display panel  2  with light, and a polarization plate  6  disposed on the side of the backlight  5  facing the viewers  10  and  20  (see  FIG. 2 ). The polarization plates  3  and  4  disposed so as to have the display panel  2  therebetween have polarization axes, namely, a first polarization axis and a second polarization axis, that are orthogonal to each other. The polarization plate  4  has a function of allowing light with the first polarization axis to pass through and absorbing light with the second polarization axis, which is substantially orthogonal to the first polarization axis. The polarization plate  3  has a function of allowing light with the second polarization axis, which is substantially orthogonal to the first polarization axis, to pass through and absorbing light with the first polarization axis. A combination of the display panel  2  and the polarization plates  3  and  4  corresponds to a so-called transmissive liquid crystal panel having a matrix of pixels arranged in an F direction and a G direction, which are orthogonal to each other. The polarization plate  6  is constructed to allow, of the light emitted from the backlight  5 , the light with the first polarization axis to pass through. The display panel  2  is connected to a controller  30  and can display an image by changing optical characteristics of each pixel in accordance with an image signal from the controller  30 . The controller  30  renders image data input from an external device (not shown) to the image display device  1  and generates an image signal.  
         [0045]     The controller  30  is electrically connected to a drive circuit  100  of the a polarization-controlled liquid crystal panel  7 , which will be described below, and outputs a switching signal to the drive circuit  100  in accordance with a change in the image display mode. In the first embodiment, the switching signal is output on the basis of a command input from an external device (not shown) connected to the image display device  1  to the controller  30 . A command to change the image display mode may be input manually by the viewer  10  or  20  via an input device such as a switch (not shown) or may be included in image data input to the image display device  1 . The controller  30  may be provided externally to the image display device  1 .  
         [0046]     The polarization-controlled liquid crystal panel  7  is disposed on the side of the polarization plate  6  facing the viewers  10  and  20 . The polarization-controlled liquid crystal panel  7  is, as shown in  FIG. 3 , a liquid crystal panel having two transparent substrates between which liquid crystal is held. The polarization-controlled liquid crystal panel  7  has a plurality of strip-shaped unit areas  7   c  arranged at pitch W in the G direction, where the F direction serves as the longitudinal direction. The polarization-controlled liquid crystal panel  7  is connected to the drive circuit  100 . The unit areas  7   c  enter one of two states by changing the liquid crystal alignment in the unit areas  7   c  on the basis of a signal from the drive circuit  100 . The two states are a transmissive state where light with the first polarization axis is allowed to pass through and a polarization state where light with the first polarization axis is changed to light with the second polarization axis, which is substantially orthogonal to the first polarization axis. The drive circuit  100  is connected to the controller  30  and controls the state of the unit areas  7   c  on the basis of a switching signal from the controller  30 .  
         [0047]     The polarization-controlled liquid crystal panel  7  alternately changes the state of the unit areas  7   c  between the transmissive state and the polarization state in units of one or two unit areas  7   c . As a result, the polarization-controlled liquid crystal panel  7  has polarization-controlled areas  7   a  for allowing light with the first polarization axis, which is emitted from the backlight  5  via the polarization plate  6 , to pass through, and polarization-controlled areas  7   b  for changing the light from having the first polarization axis to having the second polarization axis substantially orthogonal to the first polarization axis. The polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are alternately disposed in the G direction and extend in a direction substantially orthogonal to a line segment connecting a left eye  10   a  ( 20   a ) and a right eye  10   b  ( 20   b ) of the viewer  10  ( 20 ) (perpendicular to the page of  FIG. 2  (in the F direction of  FIG. 1 )).  
         [0048]     For example, when the image display device  1  is in the dual-screen display mode, the polarization-controlled liquid crystal panel  7  is controlled so that two adjacent unit areas  7   c  are in the transmissive state to form one polarization-controlled area  7   a  and that two next adjacent unit areas  7   c  are in the polarization state to form one polarization-controlled area  7   b  (state shown in  FIG. 3 ). For example, when the image display device  1  is in the three-dimensional image display mode, the polarization-controlled liquid crystal panel  7  is controlled so that the unit areas  7   c  are alternately in the transmissive state and the polarization state to form the polarization-controlled areas  7   a  and  7   b . For example, when the image display device  1  is in the two-dimensional image display mode, the polarization-controlled liquid crystal panel  7  is controlled so that the unit areas  7   c  are alternately in the transmissive state and the polarization state to form the polarization-controlled areas  7   a  and  7   b  and that the polarization-controlled areas  7   a  and  7   b  are periodically switched.  
         [0049]     As shown in  FIGS. 1 and 2 , a lenticular lens  8  is disposed on the side of the polarization-controlled liquid crystal panel  7  facing the viewers  10  and  20 . The lenticular lens  8  includes a plurality of substantially semi-cylindrical lens portions  8   a  extending in the F direction of  FIG. 1 . The lenticular lens  8  including the lens portions  8   a  has a function of guiding light separated by the polarization-controlled liquid crystal panel  7  into two beams with different polarization axes to the viewers  10  and  20  in two directions substantially orthogonal to the F direction. That is, the directions in which the light is guided by the lenticular lens  8  are directions toward the viewers  10  and  20  at different viewing positions in the dual-screen display mode and are directions toward the right eye  10   b  ( 20   b ) and the left eye ( 10   a ) of the viewer  10  ( 20 ) in the three-dimensional image display mode.  
         [0050]     A retardation film  9  is disposed between the lenticular lens  8  and the polarization plate  4  attached to the display panel  2 .  FIG. 9  is a view of the display panel viewed from the side by the viewers for describing the principle of the image display device shown in  FIG. 1 .  FIG. 10  is an exploded perspective view of the image display device for describing the principle of the image display device shown in  FIG. 1 . The retardation film  9  includes transmissive areas  9   a  for allowing light with the first polarization axis to pass through and polarization areas  9   b  for changing light with the first polarization axis to light with the second polarization axis. As shown in  FIGS. 1 and 10 , the transmissive areas  9   a  and the polarization areas  9   b  extend in the G direction substantially orthogonal to the F direction and are alternately disposed in the F direction. As shown in  FIGS. 9 and 10 , the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9  are disposed in association with pixel rows  2   a  and  2   b  that extend in the G direction of the display panel  2  and that are alternately disposed in the F direction.  
         [0051]     The structure of the polarization-controlled liquid crystal panel  7  will be described in detail below.  FIG. 4  is an exploded perspective view of the polarization-controlled liquid crystal panel  7 .  FIG. 5  is a plan view of the polarization-controlled liquid crystal panel  7 .  FIG. 6  is a sectional view of the polarization-controlled liquid crystal panel  7  taken along the line VI-VI of  FIG. 5 .  
         [0052]     The polarization-controlled liquid crystal panel  7  includes a bottom substrate  71  and a top substrate  72 , which are made of light-transmissive glass, quarts, or the like, and a liquid crystal layer  73  held between the bottom substrate  71  and the top substrate  72 . The liquid crystal layer  73  includes, for example, twisted-nematic (TN) liquid crystal or the like. On the surface of the bottom substrate  71  facing the liquid crystal layer  73 , bottom electrodes  81  and  82  made of transparent electrically-conductive films such as ITO, and an alignment film  74  for regulating the initial alignment of the liquid crystal layer  73  are disposed. On the surface of the top substrate  72  facing the liquid crystal layer  73 , top electrodes  83  and  84  made of transparent electrically-conductive films such as ITO, and an alignment film  75  for regulating the initial alignment of the liquid crystal layer  73  are disposed.  
         [0053]     As shown in  FIG. 4 , the bottom electrodes  81  and  82  are comb-like electrodes having connecting portions  81   b  and  82   b  and pluralities of strip electrodes  81   a  and  82   a . Viewed from the F direction and a direction orthogonal to the G direction, the connecting portions  81   b  and  82   b  are disposed in areas that are outside a portion of the bottom substrate  71  corresponding to a pixel area  2   c  of the display panel  2  in which the pixels are disposed and that are along two sides of the bottom substrate  71  parallel to the G direction. The strip electrodes  81   a  and  82   a  extend, parallel to the F direction, from the connecting portions  81   b  and  82   b  inward of the bottom substrate  71  in a comb-like manner.  
         [0054]     Viewed from the F direction and a direction orthogonal to the G direction, the strip electrodes  81   a  and  82   a  are formed so as to longitudinally (in the F direction) penetrate the portion of the bottom substrate  71  corresponding to the pixel area  2   c  of the display panel  2 . Viewed from the F direction and a direction orthogonal to the G direction, the strip electrodes  81   a  and  82   a  are arranged in the width direction (G direction) at pitch  2 W, which is twice the pitch W at which the unit areas  7   c  are arranged, throughout the portion of the bottom substrate  71  corresponding to the pixel area  2   c  of the display panel  2 . The bottom electrodes  81  and  82  are arranged so that the strip electrodes  81   a  and  82   a  serving as the teeth of the combs interlock one another but do not overlap one another.  
         [0055]     That is, the strip electrodes  81   a  and  82   a  extending in the F direction are alternately arranged at pitch W in the G direction in the portion of the bottom substrate  71  corresponding to the pixel area  2   c  of the display panel  2 .  
         [0056]     The top electrodes  83  and  84  are comb-like electrodes having connecting portions  83   b  and  84   b  and pluralities of strip electrodes  83   a  and  84   a . Viewed from the F direction and a direction orthogonal to the G direction, the connecting portions  83   b  and  84   b  are disposed in areas that are outside a portion of the top substrate  72  corresponding to the pixel area  2   c  of the display panel  2  in which the pixels are disposed and that are along two sides of the top substrate  72  parallel to the G direction. The strip electrodes  83   a  and  84   a  extend, parallel to the F direction, from the connecting portions  83   b  and  84   b  inward of the top substrate  72  in a comb-like manner.  
         [0057]     Viewed from the F direction and a direction orthogonal to the G direction, the strip electrodes  83   a  and  84   a  are formed so as to longitudinally (in the F direction) penetrate the portion of the top substrate  72  corresponding to the pixel area  2   c  of the display panel  2 . Viewed from the F direction and a direction orthogonal to the G direction, the strip electrodes  83   a  and  84   a  are arranged in the breadthwise direction (G direction) at pitch  4 W, which is four times the pitch W at which the unit areas  7   c  are arranged, throughout the portion of the top substrate  72  corresponding to the pixel area  2   c  of the display panel  2 . The top electrodes  83  and  84  are arranged so that the strip electrodes  83   a  and  84   a  serving as the teeth of the combs interlock one another but do not overlap one another.  
         [0058]     That is, the strip electrodes  83   a  and  84   a  extending in the F direction are alternately arranged at pitch  2 W, which is twice the pitch W at which the strip electrodes  81   a  and  82   a  are arranged, in the portion of the top substrate  72  corresponding to the pixel area  2   c  of the display panel  2 .  
         [0059]     As shown in  FIG. 5 , when the polarization-controlled liquid crystal panel  7  is in an assembled state, viewed from the F direction and a direction orthogonal to the G direction, the top electrode  83  is formed so that the longitudinal centerline of each of the strip electrodes  83   a  substantially coincides with the midline between the longitudinal centerlines of the strip electrodes  81   a  and  82   a  of the bottom electrodes  81  (area hatched with upward-sloping broken lines in  FIG. 5 ) and  82  (area hatched with downward-sloping broken lines in  FIG. 5 ). Similarly, the longitudinal centerline of each of the strip electrodes  84   a  of the top electrode  84  substantially coincides with the midline between the longitudinal centerlines of the strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82 . The short-side width of each of the strip electrodes  83   a  and  84   a  of the top electrodes  83  and  84  substantially coincides with the combined widths of the strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82 . Therefore, when the polarization-controlled liquid crystal panel  7  is in its assembled state, viewed from the F direction and a direction orthogonal to the G direction, a pair of the strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82  is superposed on each of the strip electrodes  83   a  and  84   a  of the top electrodes  83  and  84 .  
         [0060]     The unit areas  7   c  of the polarization-controlled liquid crystal panel  7  shown in  FIG. 3  correspond to areas where the strip electrodes  81   a  of the bottom electrode  81  and  82  or the strip electrodes  82   a  of the bottom electrode  82  are superposed on the strip electrodes  83   a  of the top electrode  83  or the strip electrodes  84   a  of the top electrode  84 . In other words, the alignment of the liquid crystal layer  73  is determined by potential differences in portions where the strip electrodes  81   a  or  82   a  face the strip electrodes  83   a  or  84   a , thereby forming the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7 .  
         [0061]     In the first embodiment, when a sufficient potential difference is applied between the bottom electrodes  81  and  82  and the top electrodes  83  and  84  in one unit area  7   c , this unit area  7   c  becomes the polarization-controlled area  7   a  for allowing light with the first polarization axis to pass through. When no sufficient potential difference is generated between the bottom electrodes  81  and  82  and the-top electrodes  83  and  84 , this unit area  7   c  becomes the polarization-controlled area  7   b  for changing light from having the first polarization axis to having the second polarization axis substantially orthogonal to the first polarization axis.  
         [0062]     The potential difference between the bottom electrodes  81  and  82  and the top electrodes  83  and  84  is determined by voltages applied to electrodes facing one another. The voltages applied to the electrodes are controlled by the drive circuit  100 , which will be described below.  FIG. 7  is an electrical circuit diagram of the drive circuit  100 .  
         [0063]     The drive circuit  100  includes an oscillation circuit  110 , a frequency dividing circuit  120 , AND circuits  101  to  104 , XOR circuits  105  and  106 , a NAND circuit  107 , and switches  131  to  134 . Output ends OUT 1  to OUT 4  are connected to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively.  
         [0064]     The switches  132 ,  133 , and  134  each have two (first and second) input ends, which are connected to supply voltage  5 V and to ground potential GND, respectively. An output end of the switch  132  is connected to two (first and second) input ends of the NAND circuit  107  and a first input end of the XOR circuit  105 . An output end of the switch  133  is connected to the oscillation circuit  110 . An output end of the switch  134  is connected to the frequency dividing circuit  120  and to first input ends of the circuits  101  to  104 . An output end of the switch  131  is connected to a second input end of the AND circuit  101  and a second input end of the XOR circuit  105 .  
         [0065]     The switches  131  to  134  are switched so that the output ends thereof are selectively connected to one of two (first and second) input ends thereof on the basis of a switching signal from the controller  30 .  
         [0066]     The oscillation circuit  110  is a CR oscillation circuit and has NAND circuits  111  to  113 , a capacitor  115 , resistors  116  and  117 , and a switch  118 . By supplying the supply voltage  5 V from the switch  133  to the NAND circuit  111 , the oscillation circuit  110  outputs a clock signal V 0 .  
         [0067]     The frequency of the clock signal V 0  output from the oscillation circuit  110  is selected from two different frequencies determined by the resistances of the resistors  116  and  117  depending on whether the switch  118  is connected to the resistor  116  or the resistor  117 . The switch  118  is switched so that the switch  118  is connected to one of the two resistors  116  and  117  on the basis of a switching signal from the controller  30 .  
         [0068]     The frequency dividing circuit  120  has two D-type flip flops (hereinafter referred to as “DFFs”)  121  and  122 . Of the first DFF  121 , a clock input terminal CK 1  is connected to the output of the oscillation circuit  110 , and a non-inverted output terminal QB 1  is connected to an input terminal D 1 . The first DFF  121  outputs, from an output terminal Q 1 , a clock signal V 1  at a frequency half the frequency of the clock signal V 0  input from the oscillation circuit  110 . The first DFF  121  divides the frequency of the clock signal V 0  by two to obtain the clock signal V 1  having a rectangular wave with a duty ratio of 50%.  
         [0069]     Of the second DFF  122 , a clock input terminal CK 2  is connected to the output terminal Q 1  of the first DFF  121 , and a non-inverted output terminal QB 2  is connected to an input terminal D 2 . The second DFF  122  outputs, from an output terminal Q 2 , a clock signal V 2  at a frequency half the frequency of the clock signal V 1  input from the first DFF  121 .  
         [0070]     The output terminal Q 1  of the first DFF  121  is connected to the first input end of the switch  131 , a first input end of the XOR circuit  106 , and a second input end of the AND circuit  103 . The output terminal Q 2  of the second DFF  122  is connected to the second input end of the switch  131 .  
         [0071]     An output end of the NAND circuit  107  is connected to a second input end of the XOR circuit  106 . Output ends of the XOR circuits  105  and  106  are connected to second input ends of the AND circuits  102  and  104 , respectively.  
         [0072]     Output ends of the four AN circuits  101  to  104  are connected to the output ends OUT 1  to OUT 4 , respectively. The output ends OUT 1  to OUT 4  are connected to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively. Clock signals output from the AND circuits  101  to  104  are output to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively  
         [0073]     The operation of the drive circuit  100  and the waveforms of voltages output from the drive circuit  100  to the bottom electrodes  81  and  82  and the top electrodes  83  and  84  will be described.  FIGS. 8A  to  8 C are timing charts for describing voltages output from the output ends OUT 1  to OUT 4 .  
         [0074]     In the dual-screen display mode, on the basis of a switching signal from the controller  30 , an input end of the switch  118  is connected to the resistor  116 , the input end of the switch  131  is connected to the output terminal Q 1  of the first DFF  121 , and the input end of the switch  132  is connected to the ground potential GND. The input ends of the switches  133  and  134  are connected to the supply voltage  5 V. Therefore, as shown in  FIG. 8A , the output ends OUT 1 , OUT 2 , and  0 UT 3  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 , whereas the output end OUT 4  outputs an inverted signal of the clock signal V 1 , which is inverted by the XOR circuit  106 .  
         [0075]     That is, the drive circuit  100  applies voltages to the top electrodes  83  and  84  so that the adjacent strip electrodes  83   a  and  84   a  of the top electrodes  83  and  84  have opposite phases, and the drive circuit  100  applies, to the bottom electrodes  81  and  82 , a voltage having the same phase as one of the voltages applied to the top electrodes  83  and  84 . Therefore, a potential difference is generated between the top electrode  84  and the bottom electrodes  81  and  82  facing the top electrode  84 , and, the polarization-controlled areas  7   a  and  7   b  are alternately formed every two unit areas  7   c  of the polarization-controlled liquid crystal panel  7 .  
         [0076]     In the three-dimensional image display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  116 , the input end of the switch  131  is connected to the output terminal Q 1  of the first DFF  121 , and the input end of the switch  132  is connected to the supply voltage  5 V. The input ends of the switches  133  and  134  are connected to the supply voltage  5 V. Therefore, as shown in  FIG. 8B , the output ends OUT 1 , OUT 3 , and OUT 4  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 , whereas the output end OUT 2  outputs an inverted signal of the clock signal V 1 , which is inverted by the XOR circuit  105 .  
         [0077]     That is, the drive circuit  100  applies voltages to the bottom electrodes  81  and  82  so that the adjacent strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82  have opposite phases, and the drive circuit  100  applies, to the top electrodes  83  and  84 , a voltage having the same phase as one of the voltages applied to the bottom electrodes  81  and  82 . Therefore, a potential difference is generated between the bottom electrode  82  and the top electrodes  83  and  84  facing the bottom electrode  82 , and, the polarization-controlled areas  7   a  and  7   b  are alternately formed every unit area  7   c  of the polarization-controlled liquid crystal panel  7 .  
         [0078]     In the two-dimensional image display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  117 , the input end of the switch  131  is connected to the output terminal Q 2  of the second DFF  122 , and the input end of the switch  132  is connected to the supply voltage  5 V. The input ends of the switches  133  and  134  are connected to the supply voltage  5 V. Therefore, as shown in  FIG. 8C , the output ends OUT 3  and OUT 4  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 . The output end OUT 1  outputs the clock signal V 2  output from the output terminal Q 2  of the second DFF  122 . The output end OUT 2  outputs an inverted signal of the clock signal V 2 , which is inverted by the XOR circuit  105 .  
         [0079]     That is, the drive circuit  100  applies voltages to the bottom electrodes  81  and  82  so that the adjacent strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82  have opposite phases, and the drive circuit  100  applies, to the top electrodes  83  and  84 , voltages having a period half that of the voltages applied to the bottom electrodes  81  and  82 . Therefore, a potential difference is alternately and periodically generated between the bottom electrode  81  and the top electrodes  83  and  84  and between the bottom electrode  82  and the top electrodes  83  and  84 . Thus, the polarization-controlled areas  7   a  and  7   b  are alternately formed every unit area  7   c  of the polarization-controlled liquid crystal panel  7 , and the polarization-controlled areas  7   a  and  7   b  are periodically and alternately switched. The period during which the polarization-controlled areas  7   a  and  7   b  are switched is four times the period of the clock signal V 0  determined by the resistor  117  of the oscillation circuit  110  and is 1/60 seconds in the first embodiment.  
         [0080]     Next, the operation of the image display device  1  of the first embodiment will be described in detail.  
         [0000]     Dual-screen Display Mode  
         [0081]     With reference to  FIGS. 2 and 9  to  11 , the operation of the image display device  1  of the first embodiment in the dual-screen display mode will be described.  FIG. 11  is a diagram for describing areas of the display panel viewed by the viewers in the dual-screen display mode of the image display device of the first embodiment shown in  FIG. 1 .  
         [0082]     Image data including information about two different images is input from an external device to the controller  30 . At the same time, the external device gives an image display mode switching command to the controller  30 . By supplying image signals from the controller  30  to the display panel  2 , images are displayed on the display panel  2 . The image signals supplied from the controller  30  are two image signals for an image L 2  (e.g., a television image) and an image R 2  (e.g., a car navigation image). Tn the first embodiment, as shown in  FIG. 10 , in the dual-screen display mode, the image L 2  is displayed in the pixel rows  2   a  of the display panel  2 , and the image R 2  is displayed in the pixel rows  2   b  of the display panel  2 .  
         [0083]     With reference to  FIGS. 2 and 10 , the structure of the polarization-controlled liquid crystal panel  7  and the display panel  2  for providing different images to the viewers  10  and  20  at different viewing positions will be described. in the image display device  1  in the dual-screen display mode, as shown in  FIG. 2 , a pair of the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  is provided for each of the lens portions  8   a  of the lenticular lens  8 . That is, in the dual-screen display mode, as has been described above, the polarizatton-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  each include two unit areas  7   c  (see  FIG. 3 ).  
         [0084]     With this structure, light emitted from the backlight  5  is routed to the polarization plate  6 , which is disposed on the side of the backlight  5  facing the viewers  10  and  20 , and only light with the first polarization axis is allowed to pass through the polarization plate  6  toward the polarization-controlled liquid crystal panel  7 . The light with the first polarization axis passes through the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7 . In this case, the light entering the polarization-controlled areas  7   a  of the polarization-controlled liquid crystal panel  7  is allowed to pass through the polarization-controlled areas  7   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization-controlled areas  7   b  of the polarization-controlled liquid crystal panel  7  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization-controlled areas  7   b . Thereafter, as shown in  FIG. 2 , the light with the first polarization axis, which comes from the polarization-controlled areas  7   a , is collected by the lenticular lens  8  so that the light is directed to the viewer  10 . The light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization-controlled areas  7   b , is collected by the lenticular lens  8  so that the light is directed to the viewer  20 .  
         [0085]     As shown in  FIG. 10 , the light with the first polarization axis, which is directed to the viewer  10 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the first polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization areas  9   b . Thereafter, the light with the first polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the viewer  10 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   a  of the display panel  2 . In contrast, the light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the viewer  10 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   b  of the display panel  2  displaying the image R 2  reaches the viewer  10 , and the viewer  10  cannot see the image R 2  displayed in the pixel rows  2   b  of the display panel  2 . Accordingly, the viewer  10  can see only the image L 2  displayed in the pixel rows  2   a  of the display panel  2 , as shown in  FIG. 11 .  
         [0086]     As shown in  FIG. 10 , the light with the second polarization axis, which is directed to the viewer  20 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the second polarization axis substantially orthogonal to the first polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the first polarization axis exits from the polarization areas  9   b . Thereafter, the light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the viewer  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   a  of the display panel  2  displaying the image L 2  reaches the viewer  20 , and the viewer  20  cannot see the image L 2  displayed in the pixel rows  2   a  of the display panel  2 . In contrast, the light with the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the viewer  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   b  of the display panel  2 . Accordingly, the viewer  20  can see only the image R 2  displayed in the pixel rows  2   b  of the display panel  2 , as shown in  FIG. 11 ,  
         [0000]     Three-dimensional Image Display Mode  
         [0087]     Next, the operation of the image display device  1  of the first embodiment in the three-dimensional image display mode will be described with reference to FIGS.  12  to  14 .  FIG. 12  is a view of the display panel viewed from the top by the viewers for describing the principle. Of displaying a three-dimensional image by the image display device of the first embodiment shown in  FIG. 1 .  FIG. 13  is an exploded perspective view of the image display device for describing the principle of displaying a three-dimensional image by the image display device.  FIG. 14  is a diagram for describing areas of the display panel viewed by the viewers in the three-dimensional image display mode of the image display device.  
         [0088]     Image data including information about two different images is input from an external device to the controller  30 . At the same time, the external device gives an image display mode switching command to the controller  30 . By supplying image signals from the controller  30  to the display panel  2 , images are displayed on the display panel  2 . The image signals supplied from the controller  30  are two image signals for a left-eye image L 3  entering the left eyes  10   a  and  20   a  of the viewers  10  and  20  and a right-eye image R 3  entering the right eyes  10   b  and  20   b  of the viewers  10  and  20 . In the first embodiment, as shown in  FIG. 13 , in the three-dimensional image display mode, the left-eye image L 3  is displayed in the pixel rows  2   a  of the display panel  2 , and the right-eye image R 3  is displayed in the pixel rows  2   b  of the display panel  2 .  
         [0089]     The structure of the polarization-controlled liquid crystal panel  7  and the display panel  2  for providing a three-dimensional image to the viewers  10  and  20  at different viewing positions will be described. As shown in  FIG. 12 , two pairs of the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are provided for each of the lens portions  8   a  of the lenticular lens  8 . That is, in the three-dimensional image display mode, as has been described above, the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  each include one unit area  7   c  (see  FIG. 3 ).  
         [0090]     With this structure, light emitted from the backlight  5  is routed to the polarization plate  6 , which is disposed on the side of the backlight  5  facing the viewers  10  and  20 , and only light with the first polarization axis is allowed to pass through the polarization plate  6  toward the polarization-controlled liquid crystal panel  7 . The light with the first polarization axis passes through the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7 . In this case, the light entering the polarization-controlled areas  7   a  of the polarization-controlled liquid crystal panel  7  is allowed to pass through the polarization-controlled areas  7   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization-controlled areas  7   b  of the polarization-controlled liquid crystal panel  7  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization-controlled areas  7   b . Thereafter, the light with the first polarization axis, which comes from the polarization-controlled areas  7   a , is collected by the lenticular lens  8  so that the light is directed to the left eyes  10   a  and  20   a  of the viewers  10  and  20 . The light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization-controlled areas  7   b , is collected by the lenticular lens  8  so that the light is directed to the right eyes  10   b  and  20   b  of the viewers  10  and  20 .  
         [0091]     As shown in  FIG. 13 , the light with the first polarization axis, which is directed to the left eyes  10   a  and  20   a  of the viewers  10  and  20 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the first polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization areas  9   b . Thereafter, the light with the first polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the left eyes  10   a  and  20   a  of the viewers  10  and  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   a  of the display panel  2 . In contrast, the light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the left eyes  10   a  and  20   a  of the viewers  10  and  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   b  of the display panel  2  displaying the right-eye image R 3  reaches the left eyes  10   a  and  20   a  of the viewers  10  and  20 , and the left eyes  10   a  and  20   a  of the viewers  10  and  20  cannot see the right-eye image R 3  displayed in the pixel rows  2   b  of the display panel  2 . Accordingly, only the left-eye image L 3  displayed in the pixel rows  2   a  of the display panel  2  enters the left eyes  10   a  and  20   a  of the viewers  10  and  20 , as shown in  FIG. 14 .  
         [0092]     As shown in  FIG. 13 , the light with the second polarization axis, which is directed to the right eyes  10   b  and  20   b  of the viewers  10  and  20 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the second polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the first polarization axis exits from the polarization areas  9   b . Thereafter, the light with the second polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the right eyes  10   b  and  20   b  of the viewers  10  and  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   a  of the display panel  2  displaying the left-eye image L 3  reaches the right eyes  10   b  and  20   b  of the viewers  10  and  20 , and the right eyes  10   b  and  20   b  of the viewers  10  and  20  cannot see the left-eye image L 3  displayed in the pixel rows  2   a  of the display panel  2 . In contrast, the light with the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the right eyes  10   b  and  20   b  of the viewers  10  and  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   b  of the display panel  2 . Accordingly, the right-eye image R 3  displayed in the pixel rows  2   b  of the display panel  2  enters the right eyes  10   b  and  20   b  of the viewers  10  and  20 , as shown in  FIG. 14 . As has been described above, the left-eye image L 3  and the right-eye image R 3  having binocular parallax enter the left and right eyes of the viewers  10  and  20 , respectively, and hence, the viewers  10  and  20  can see a three-dimensional image.  
         [0000]     Two-dimensional Image Display Mode with Less Image Deterioration  
         [0093]     Next, the operation of the image display device  1  of the first embodiment in the two-dimensional image display mode will be described with reference to  FIGS. 12, 15 , and  16 .  FIG. 15  is a diagram showing the polarization-controlled liquid crystal panel, the retardation film, and the display panel in the two-dimensional image display mode of the image display device.  FIG. 16  is a diagram describing areas of the display panel viewed by the viewers in the two-dimensional image display mode of the image display device.  
         [0094]     Image data is input from an external device to the controller  30 . At the same time, the external device gives an image display mode switching command to the controller  30 . As shown in  FIG. 15 , in the two-dimensional image display mode, a two-dimensional image Sl is displayed on the display panel  2  from 0/120 seconds to 2/120 seconds, and a two-dimensional image S 2  is displayed from 2/120 seconds to 4/120 seconds. The two-dimensional images S 1  and S 2  are sequentially and alternately displayed every 1/60 seconds.  
         [0095]     The structure of the polarization-controlled liquid crystal panel  7  and the display panel  2  for providing a two-dimensional image to the viewers  10  and  20  at different viewing positions will be described. Two pairs of the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are provided for each of the lens portions  8   a  of the lenticular lens  8 , as in the three-dimensional image display mode shown in  FIG. 12 . That is, in the two-dimensional image display mode with less image deterioration, the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  each include one unit area  7   c  (see  FIG. 3 ).  
         [0096]     In the two-dimensional image display mode, the polarization-controlled liquid crystal panel  7  is controlled so that the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are switched every ½ frame period of the display panel  2  (every 1/120 seconds) with the above-described structure, as shown in  FIGS. 15 and 16 , from 0/120 seconds to 1/120 seconds, the two-dimensional image S 1  displayed in the pixel rows  2   a  of the display panel  2  enters the left eyes  10   a  and  20   a  of the viewers  10  and  20 , and the two-dimensional image S 1  displayed in the pixel rows  2   b  of the display panel  2  enters the right eyes  10   b  and  20   b  of the viewers  10  and  20 . From 1/120 seconds to 2/120 seconds, the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are controlled so that the polarization-controlled areas  7   a  and  7   b  are switched. Thus, light directed to the left eyes  10   a  and  20   a  of the viewers  10  and  20  passes through the polarization-controlled areas  7   b  of the polarization-controlled liquid crystal panel  7 , the polarization axis of which is changed substantially by 90 degrees, and the light with the changed polarization axis is routed toward the retardation film  9 . Therefore, as shown in  FIG. 16 , from 1/120 seconds to 2/120 seconds, the two-dimensional image S 1  displayed in the pixel rows  2   b  of the display panel  2  enters the left eyes  10   a  and  20   a  of the viewers  10  and  20 , and the two-dimensional image S 1  displayed in the pixel rows  2   a  of the display panel  2  enters the right eyes  10   b  and  20   b  of the viewers  10  and  20 .  
         [0097]     From 2/120 seconds to 3/120 seconds, as in the interval from 0/120 seconds to 1/120 seconds, the two-dimensional image S 2  displayed in the pixel rows  2   a  of the display panel  2  enters the left eyes  10   a  and  20   a  of the viewers  10  and  20 , and the two-dimensional image S 2  displayed in the pixel rows  2   b  of the display panel  2  enters the right eyes  10   b  and  20   b  of the viewers  10  and  20 . From 3/120 seconds to 4/120 seconds, as in the interval from 1/120 seconds to 2/120 seconds, the two-dimensional image S 2  displayed in the pixel rows  2   b  of the display panel  2  enters the left eyes  10   a  and  20   a  of the viewers  10  and  20 , and the two-dimensional image S 2  displayed in the pixel rows  2   a  of the display panel  2  enters the right eyes  10   b  and  20   b  of the viewers  10  and  20 . In this manner, a two-dimensional image S displayed in the entire display panel  2  enters the left and right eyes of the viewers  10  and  20  within 2/120 seconds ( 1/60 seconds). Accordingly, a two-dimensional image with less deterioration can be provided to the viewers  10  and  20 .  
         [0098]     The image display device of the first embodiment described above has the following advantages.  
         [0099]     Between the backlight  5  and the display panel  2 , the polarization-controlled liquid crystal panel  7  is disposed to separate light emitted from the backlight  5  through the polarization plate  6  into a light beam with the first polarization axis and a light beam with the second polarization axis substantially orthogonal to the first polarization axis. Between the polarization-controlled liquid crystal panel  7  and the display panel  2 , the lenticular lens  8  is provided to route the light beams with different polarization axes, which are separated by the polarization-controlled liquid crystal panel  71  in predetermined directions. Accordingly, the light emitted from the backlight  5  can be separated, before entering the display panel  2 , into light beams directed to the viewers  10  and  20  at different viewing positions. Even when a high-resolution display panel  2  with a small pixel pitch is used, the light is directed to the viewers  10  and  20  regardless of the pixel pitch of the display panel  2 . Therefore, a high-resolution image can be provided to the viewers  10  and  20  at different viewing positions.  
         [0100]     Because the lenticular lens  8  is provided to direct the light beams with different polarization axes, which are separated by the polarization-controlled liquid crystal panel  7 , in predetermined associated directions, the light beams directed to the viewers  10  and  20  are not blocked, unlike the case where the light coming from the display panel  2  is directed to pass through a member that restricts the light to be routed in directions with predetermined angles. Therefore, the luminance of light directed to the viewers  10  and  20  is prevented from decreasing, and hence an image is prevented from being displayed as a dark image.  
         [0101]     The polarization-controlled liquid crystal panel  7  is provided with the polarization-controlled areas  7   a  for allowing light with the first polarization axis to pass through, and the polarization-controlled areas  7   b  for changing light from having the first polarization axis to having the second polarization axis substantially orthogonal to the first polarization axis. The lenticular lens  8  is provided with the substantially semi-cylindrical lens portions  8   a  each of which is associated with a pair of the polarization-controlled areas  7   a  and  7   b . Hence, light with the first polarization axis and light with the second polarization axis substantially orthogonal to the first polarization axis are separately directed by the lens portions  8   a  of the lenticular lens  8  to the viewers  10  and  20  at different viewing positions. Therefore, different images can be easily provided to the viewers  10  and  20  at different viewing positions.  
         [0102]     Since the display panel  2  is provided with the pixel rows  2   a  and  2   b  in association with the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  91  which extend in the G direction of  FIG. 1 , light passing through the transmissive areas  9   a  of the retardation film  9  can be directed to enter the pixel rows  2   a  of the display panel  2  and to be routed to the viewer  10  while maintaining the image L 2  being displayed in the pixel rows  2   a  of the display panel  2  (see  FIG. 9 ). Also, light passing through the polarization areas  9   b  can be directed to enter the pixel rows  2   b  of the display panel  2  and to be routed to the viewer  20  while maintaining the image R 2  being displayed in the pixel rows  2   a  of the display panel  2  (see  FIG. 9 ). Accordingly, different images can be provided to the viewers  10  and  20  at different viewing positions.  
         [0103]     By controlling the voltages applied to the bottom electrodes  81  and  82  and the top electrodes  83  and  84  of the polarization-controlled liquid crystal panel  7 , the polarization-controlled areas  7   a  for allowing light with the first polarization axis to pass through and the polarization-controlled areas  7   b  for changing light from having the first polarization axis to having the second polarization axis substantially orthogonal to the first polarization axis can be easily formed on the polarization-controlled liquid crystal panel  7 . Therefore, the polarization axis of light emitted from the backlight  5  can be easily controlled. Accordingly, light emitted from the backlight  5  is directed through the segmented polarization-controlled areas  7   a  and  7   b  to enter the lens portions  8   a  of the lenticular lens  8 , thereby breaking a light-reaching area into segments. Since the light-reaching area can be broken into segments corresponding to the right eye  10   b  ( 20   b ) and the left eye  10   a  ( 20   a ) of the viewer  10  ( 20 ), images having binocular parallax can be directed to enter the left eye  10   a  ( 20   a ) and the right eye  10   b  ( 20   b ) of the viewer  10  ( 20 ). Accordingly, a three-dimensional image can be provided to the viewers  10  and  20  at different viewing positions.  
         [0104]     The bottom electrodes  81  and  82  of the polarization-controlled liquid crystal panel  7  have comb-like shapes, and the bottom electrodes  81  and  82  are disposed on the bottom substrate  71  so that the strip electrodes  81   a  and  82   a  interlock one another. Similarly, the top electrodes  83  and  84  have comb-like shapes, and the top electrodes  83  and  84  are disposed on the top substrate  72  so that the strip electrodes  83   a  and  84   a  interlock one another. Therefore, two electrodes to which different voltages are applied can be fabricated using a single electrically-conductive layer on each substrate, and hence the polarization-controlled liquid crystal panel  7  can be easily fabricated. The pitch at which the strip electrodes are arranged can be easily reduced.  
         [0105]     Since the drive circuit  100  for controlling the polarization-controlled liquid crystal panel  7  includes a combination of a simple known electrical circuit including the oscillation circuit  110 , the frequency dividing circuit  120 , and a logic circuit, the drive circuit  100  can be easily fabricated.  
         [0106]     Next, a specific example of an electronic apparatus to which the image display device of the first embodiment is applicable will be described with reference to  FIG. 17 .  
         [0107]     The case where the image display device of the first embodiment is applied to a display unit of a cellular phone will be described.  FIG. 17  is a perspective view of the structure of the cellular phone. As shown in  FIG. 17 , a cellular phone  200  includes a plurality of operation buttons  201 , an earpiece  202 , a mouthpiece  203 , and a display unit  204  to which the image display device of the first embodiment is applied.  
         [0108]     Electronic apparatuses to which the image display device of the first embodiment is applicable include, besides the cellular phone shown in  FIG. 17 , a personal computer, a liquid crystal television, a viewfinder-/monitor-direct-view-type video tape recorder, a car navigation apparatus, a pager, an electronic notebook, an electronic calculator, a word-processor, a workstation, a videophone, a point-of-sale (POS) terminal, a digital still camera, or the like.  
       Second Embodiment  
       [0109]     A second embodiment of the invention will be described with reference to  FIGS. 18 and 19 A to  19 D.  
         [0110]     An image display device of the second embodiment differs from the image display device  1  of the first embodiment only in the structure of the drive circuit  100 . In the second embodiment, components similar to those of the image display device  1  of the first embodiment are given the same reference numerals, and repeated descriptions thereof will be omitted appropriately.  
         [0111]     The image display device  1  of the second embodiment has three image display modes, namely, the dual-screen display mode in which different images are provided to the viewers  10  and  20  residing at different viewing positions, the three-dimensional image display mode in which a three-dimensional image is provided to the viewers  10  and  20 , and the two-dimensional image display mode in which one and the same two-dimensional image is provided to the viewers  10  and  20 . By switching among these image display modes, the image display device  1  can provide images in various modes. The dual-screen display mode of the second embodiment differs from the first embodiment in that it has two modes, namely, a first dual-screen display mode in which the image L 2  is provided to the viewer  10  and simultaneously the image R 2  is provided to the viewer  20 , and a second dual-screen display mode in which, in contrast to the first dual-screen display mode, the image R 2  is provided to the viewer  10  and simultaneously the image L 2  is provided to the viewer  20 . In the second embodiment, the first and second dual-screen display modes are switched.  
         [0112]     The structure and operation of a drive circuit  300  for controlling the polarization-controlled liquid crystal panel  7  of the second embodiment will be described.  FIG. 18  is an electrical circuit diagram of the control circuit, and  FIGS. 19A  to  19 D are timing charts for describing voltages output from output ends.  
         [0113]     The drive circuit  300  includes the oscillation circuit  110 , the frequency dividing circuit  120 , AND circuits  301  to  305 , XOR circuits  306  to  309 , a NAND circuit  310 , and switches  331  to  335 , Output ends OUT 1  to OUT 4  are connected to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively.  
         [0114]     The switches  332 ,  333 ,  334 , and  335  each have two (first and second) input ends, which are connected to supply voltage  5 V and ground potential GND, respectively. An output end of the switch  332  is connected to two (first and second) input ends of the NAND circuit  310  and a first input end of the XOR circuit  306 . An output end of the switch  333  is connected to the oscillation circuit  110 . An output end of the switch  334  is connected to the frequency dividing circuit  120  and first input ends of the AND circuits  301  to  304 . An output end of the switch  335  is connected to a first input end of the AND circuit  305 . An output end of the switch  331  is connected to a second input end of the AND circuit  301  and a second input end of the XOR circuit  306 .  
         [0115]     The switches  331  to  335  are switched so that the output ends thereof are selectively connected to one of two (first and second) input ends thereof on the basis of a switching signal from the controller  30 .  
         [0116]     The oscillation circuit  110  is, as in the first embodiment, a CR oscillation circuit. By supplying the supply voltage  5 V from the switch  333  to the NAND circuit  111 , the oscillation circuit  110  outputs a clock signal V 0 . The frequency of the clock signal V 0  output from the oscillation circuit  110  is selected from two different frequencies determined by the resistances of the resistors  116  and  117  depending on whether the switch  118  is connected to the resistor  116  or the resistor  117 . The switch  118  is switched so that the switch  118  is connected to one of the two resistors  116  and  117  on the basis of a switching signal from the controller  30 .  
         [0117]     The frequency dividing circuit  120  has, as in the first embodiment, the two D-type flip flops (hereinafter referred to as “DFFs”)  121  and  122 . Of the first DFF  121 , the clock input terminal CK 1  is connected to the output of the oscillation circuit  110 , and the non-inverted output terminal QB 1  is connected to the input terminal D 1 . The first DFF  121  outputs, from the output terminal Q 1 , the clock sign V 1  at a frequency half the frequency of the clock signal V 0  input from the oscillation circuit  110 . The first DFF  121  divides the frequency of the clock signal V 0  by two to obtain the clock signal V 1  having a rectangular wave with a duty ratio of 50%.  
         [0118]     Of the second DFF  122 , the clock input terminal CK 2  is connected to the output terminal Q 1  of the first DFF  121 , and the non-inverted output terminal QB 2  is connected to the input terminal D 2 . The second DFF  122  outputs, from the output terminal Q 2 , the clock signal V 2  at a frequency half the frequency of the clock signal V 1  input from the first DFF  121 .  
         [0119]     The output terminal Q 1  of the first DFF  121  is connected to the first input end of the switch  331  and first input ends of the XOR circuits  307  and  308 . The output terminal Q 2  of the second DFF  122  is connected to the second input end of the switch  331 .  
         [0120]     An output end of the NAND circuit  310  is connected to a second input end of the AND circuit  305  and a first input end of the XOR circuit  309 . An output end of the AND circuit  305  is connected to second input ends of the XOR circuits  307  and  309 . An output end of the XOR circuit  309  is connected to a second input end of the XOR circuit  308 . Output ends of the XOR circuits  306  to  308  are connected to second input ends of the AND circuits  302  to  304 , respectively.  
         [0121]     Output ends of the four AND circuits  301  to  304  are connected to the output ends OUT 1  to OUT 4 , respectively. The output ends OUT 1  to OUT 4  are connected to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively. Clock signals output from the AND circuits  301  to  304  are output to the bottom electrodes  81  and  82  and the top electrodes  83  and  84 , respectively.  
         [0122]     The operation of the drive circuit  300  and the waveforms of voltages output from the drive circuit  300  to the bottom electrodes  81  and  82  and the top electrodes  83  and  84  will be described.  
         [0123]     In the first dual-screen display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  116 , the input end of the switch  331  is connected to the output terminal Q 1  of the first DFF  121 , and the input ends of the switches  332  and  335  are connected to the ground potential GND. The input ends of the switches  333  and  334  are connected to the supply voltage  5 V. Therefore, as shown in  FIG. 19A , the output ends OUT 1 , OUT 2 , and OUT 3  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 , whereas the output end OUT 4  outputs an inverted signal of the clock signal V 1 , which is inverted by the XOR circuit  308 .  
         [0124]     In the second dual-screen display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  116 , the input end of the switch  331  is connected to the output terminal Q 1  of the first DFF  121 , and the input end of the switch  332  is connected to the ground potential GND. The input ends of the switches  333 ,  334 , and  335  are connected to the supply voltage  5 V. Therefore, as shown in  FIG. 19B , the output ends OUT 1 , OUT 2 , and OUT 4  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 , whereas the output end OUT 3  outputs an inverted signal of the clock signal V 1 , which is inverted by the XOR circuit  307 .  
         [0125]     That is, the drive circuit  300  applies voltages to the top electrodes  83  and  84  so that the adjacent strip electrodes  83   a  and  84   a  of the top electrodes  83  and  84  have opposite phases, and the drive circuit  300  applies, to the bottom electrodes  81  and  82 , a voltage having the same phase as one of the voltages applied to the top electrodes  83  and  84 . Therefore, a potential difference is generated between the strip electrodes  84   a  and the strip electrodes  81   a  and  82   a  facing the strip electrodes  84   a  in the first dual-screen display mode. This is the same as the case of the dual-screen display mode of the first embodiment. In the second dual-screen display mode, a potential difference is generated between the strip electrodes  83   a  and the strip electrodes  81   a  and  82   a  facing the strip electrodes  83   a . Hence, the polarization-controlled areas  7   a  and  7   b  are alternately formed every two unit areas  7   c  of the polarization-controlled liquid crystal panel  7 , The unit areas  7   c  in which the polarization-controlled areas  7   a  and  7   b  are formed are inverted in position between the first and second dual-screen display modes.  
         [0126]     In the three-dimensional image display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  116 , the input end of the switch  331  is connected to the output terminal Q 1  of the first DFF  121 , and the input ends of the switches  332 ,  333 , and  334  are connected to the supply voltage  5 V. The input end of the switch  335  is connected to the ground potential GND. Therefore, as shown in  FIG. 19C , the output ends OUT 1 , OUT 3 , and OUT 4  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 , whereas the output end OUT 2  outputs an inverted signal of the clock signal V 1 , which is inverted by the XOR circuit  306 .  
         [0127]     That is, the drive circuit  300  applies, as in the first embodiment, voltages to the bottom electrodes  81  and  82  so that the adjacent strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82  have opposite phases, and the drive circuit  300  applies, to the top electrodes  83  and  84 , a voltage having the same phase as one of the voltages applied to the bottom electrodes  81  and  82 . Therefore, a potential difference is generated between the bottom electrode  82  and the top electrodes  83  and  84  facing the bottom electrode  82 , and, the polarization-controlled areas  7   a  and  7   b  are alternately formed every unit area  7   c  of the polarization-controlled liquid crystal panel  7 .  
         [0128]     In the two-dimensional image display mode, on the basis of a switching signal from the controller  30 , the input end of the switch  118  is connected to the resistor  117 , the input end of the switch  331  is connected to the output terminal Q 2  of the second DFF  122 , and the input end of the switch  332  is connected to the supply voltage  5 V. The input ends of the switches  333  and  334  are connected to the supply voltage  5 V. The input end of the switch  335  is connected to the ground potential GND. Therefore, as shown in  FIG. 19D , the output ends OUT 3  and OUT 4  output the clock signal V 1  output from the output terminal Q 1  of the first DFF  121 . The output end OUT 1  outputs the clock signal V 2  output from the output terminal Q 2  of the second DFF  122 . The output end OUT 2  outputs an inverted signal of the clock signal V 2 , which is inverted by the XOR circuit  306 .  
         [0129]     That is, the drive circuit  300  applies, as in the first embodiment, voltages to the bottom electrodes  81  and  82  so that the adjacent strip electrodes  81   a  and  82   a  of the bottom electrodes  81  and  82  have opposite phases, and the drive circuit  300  applies, to the top electrodes  83  and  84 , voltages having a period half that of the voltages applied to the bottom electrodes  81  and  82 . Therefore, a potential difference is alternately and periodically generated between the bottom electrode  81  and the top electrodes  83  and  84  and between the bottom electrode  82  and the top electrodes  83  and  84 . Thus, the polarization-controlled areas  7   a  and  7   b  are alternately formed every unit area  7   c  of the polarization-controlled liquid crystal panel  7 , and the polarization-controlled areas  7   a  and  7   b  are periodically and alternatively switched. The period during which the polarization-controlled areas  7   a  and  7   b  are switched is four times the period of the clock signal V 0  determined by the resistor  117  of the oscillation circuit  110  and is 1/60 seconds in the second embodiment.  
         [0130]     Next, the operation of the image display device  1  of the second embodiment will be described in detail.  
         [0131]     Since the operation of the image display device  1  of the second embodiment is the same as that of the first embodiment except for the operation in the second dual-screen display mode, a repeated description thereof will be omitted.  
         [0000]     First Dual-screen Display Mode  
         [0132]     Since the first dual-screen display mode is the same as the dual-screen display mode of the first embodiment, a repeated description thereof is omitted. in the first dual-screen display mode, as has been described above, by supplying image signals from the controller  30  to the display panel  2 , two different images, namely, the image L 2  and the image R 2 , are simultaneously displayed on the display panel  2 . However, the light directed to the viewer  10  only passes through the pixel rows  2   a  of the display panel  2  displaying the image L 2 , and the light directed to the viewer  20  only passes through the pixel rows  2   b  of the display panel  2  displaying the image R 2 . Thus, only the image L 2  is viewed by the viewer  10 , whereas only the image R 2  is viewed by the viewer  20 .  
         [0000]     Second Dual-screen Display Mode  
         [0133]     In the second dual-screen display mode, image data supplied from the external device to the controller  30  is the same as that in the first dual-screen display mode. The image signals supplied from the controller  30  to the display panel  2  are the same as those in the first dual-screen display mode. Therefore, as shown in  FIG. 10 , in the second dual-screen display mode, the image L 2  is displayed in the pixel rows  2   a  of the display panel  2 , and the image R 2  is displayed in the pixel rows  2   b  of the display panel  2 .  
         [0134]     By giving an image display mode switching command from the external device to the controller  30 , the output from the drive circuit  300  is switched, and the unit areas  7   c  in which the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7  are formed are inverted in position from those in the first dual-screen display mode.  
         [0135]     With this structure, light emitted from the backlight  5  is routed to the polarization plate  6 , which is disposed on the side of the backlight  5  facing the viewers  10  and  20 , and only light with the first polarization axis is allowed to pass through the polarization plate  6  toward the polarization-controlled liquid crystal panel  7 . The light with the first polarization axis passes through the polarization-controlled areas  7   a  and  7   b  of the polarization-controlled liquid crystal panel  7 . In this case, the light entering the polarization-controlled areas  7   a  of the polarization-controlled liquid crystal panel  7  is allowed to pass through the polarization-controlled areas  7   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization-controlled areas  7   b  of the polarization-controlled liquid crystal panel  7  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization-controlled areas  7   b . Thereafter, the light with the first polarization axis, which comes from the polarization-controlled areas  7   a , is collected by the lenticular lens  8  so that the light is directed to the viewer  20 . The light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization-controlled areas  7   b , is collected by the lenticular lens  8  so that the light is directed to the viewer  10 . That is, the polarization axes of the light beams directed to the viewers  10  and  20  are switched from those in the first dual-screen display mode.  
         [0136]     The light with the first polarization axis, which is directed to the viewer  20 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the first polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the second polarization axis exits from the polarization areas  9   b . Thereafter, the light with the first polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the viewer  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   a  of the display panel  2 . In contrast, the light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the viewer  20 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   b  of the display panel  2  displaying the image R 2  reaches the viewer  20 , and the viewer  20  cannot see the image R 2  displayed in the pixel rows  2   b  of the display panel  2 . Accordingly, the viewer  20  can see only the image L 2  displayed in the pixel rows  2   a  of the display panel  2 .  
         [0137]     The light with the second polarization axis, which is directed to the viewer  10 , enters the retardation film  9  having the transmissive areas  9   a  and the polarization areas  9   b . The light with the second polarization axis substantially orthogonal to the first polarization axis passes through the transmissive areas  9   a  and the polarization areas  9   b  of the retardation film  9 . In this case, the light passing through the transmissive areas  9   a  of the retardation film  9  is allowed to pass through the transmissive areas  9   a  without changing the polarization axis. In contrast, the polarization axis of the light entering the polarization areas  9   b  is changed substantially by 90 degrees, and the light with the first polarization axis exits from the polarization areas  9   b . Thereafter, the light with the second polarization axis substantially orthogonal to the first polarization axis, which comes from the transmissive areas  9   a  of the retardation film  9  and which is directed to the viewer  10 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9  and is absorbed by the polarization plate  4 . Thus, no light passing through the pixel rows  2   a  of the display panel  2  displaying the image L 2  reaches the viewer  10 , and the viewer  10  cannot see the image L 2  displayed in the pixel rows  2   a  of the display panel  2 . In contrast, the light with the first polarization axis, which comes from the polarization areas  9   b  of the retardation film  9  and which is directed to the viewer  10 , enters the polarization plate  4  disposed between the display panel  2  and the retardation film  9 , passes through the polarization plate  4 , and enters the pixel rows  2   b  of the display panel  2 . Accordingly, the viewer  10  can see only the image R 2  displayed in the pixel rows  2   b  of the display panel  2 .  
         [0138]     That is, the image display device  1  of the second embodiment provides only the image L 2  to the viewer  10  and only the image R 2  to the viewer  20  in the first dual-screen display mode. In the second dual-screen display mode, the image display device  1  provides only the image R 2  to the viewer  10  and only the image L 2  to the viewer  20 .  
         [0139]     The image display device  1  of the second embodiment described above has the following advantages.  
         [0140]     In the image display device  1  of the second embodiment, images provided to the viewers  10  and  20  at different viewing positions can be switched by changing the manner in which the polarization-controlled liquid crystal panel  7  is controlled, without changing the image data input from the external device to the controller  30  or the image signals supplied from the controller  30  to the display panel  2 . That is, the directions in which images are displayed can be switched.  
         [0141]     For example, when similarly switching the directions in which images are provided, a known dual-screen display device using a parallax barrier involves switching the positions at which the images L 2  and R 2  are displayed. Therefore, in the known dual-screen display device, the input image data needs to be re-rendered and new image signals need to be generated every time the positions at which images are displayed are switched. When switching the directions in which images are displayed, it requires time for the known dual-screen display device to re-render the image data, resulting in a delay in displaying images, To prevent the delay in displaying images, an additional memory is necessary, which leads to an increase in the cost of the display device.  
         [0142]     However, in the image display device  1  of the second embodiment, the images provided to the viewers  10  and  20  at different viewing positions can be switched instantly without needing to switch the positions at which the images L 2  and R 2  are displayed. As a result, no delay occurs in displaying the images upon the switching operation. Therefore, the viewers  10  and  20  can view the images L 2  and R 2  in a more comfortable manner. There is no need to have an additional memory, and the image display device  1  can be fabricated at low cost.  
         [0143]     In the second embodiment, the first and second dual-screen display modes of the image display device  1  are switched by giving an image display mode switching command from the external device to the controller  30 . However, the display mode switching is not limited thereto. For example, the first and second dual-screen display modes may be sequentially switched every predetermined time using a timer.  
         [0144]     The other advantages of the second embodiment and the structure of an electronic apparatus are the same as those of the first embodiment.  
         [0145]     The invention is not limited to the embodiments described above. Various changes, alterations, and modifications are possible without departing from the scope of the invention set forth in claims and the entire specification.