Patent Publication Number: US-6211927-B1

Title: Display system for viewing images on the front and back surfaces of a screen

Description:
This is a divisional of U.S. application Ser. No. 08/767,317, filed Dec. 16, 1996, now U.S. Pat. No. 6,055,027. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display unit and a display system thereof which allow a stereoscopic image or different images to be displayed on the same screen. 
     2. Description of Related Art 
     Hitherto, there has been known a technology for obtaining stereoscopic images by forming images for right and left eyes by utilizing two projectors and by viewing them by right and left eyes, respectively (see Chihiro Masuda, Three-Dimensional Display, Sangyo Publishing Co., 1990). 
     There have been also known a front projection method and a rear projection method as methods for displaying stereoscopic images. It has been common so far that the front projection method projecting stereoscopic images on a silver screen is performed to show to many people in events or the like. 
     On the other hand, the rear projection method of projecting polarized stereoscopic images has been very rare so far. Because the polarization characteristics of the image light degrades in passing through the screen due to scattering and the like, thus failing to give stereoscopic view or causing after-image and dark screen. It has been difficult to let the light pass through the screen while maintaining the polarization characteristics, especially when circularly polarized light is used. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the aforementioned problems of the rear projection method by providing means which allows to transmit image lights using circularly polarized light to observers without degrading the polarization characteristics by an optical system such as lenses and the screen. 
     According to the present invention, a display unit is provided with first and second liquid crystal panels for displaying images, and linearly polarized image lights output respectively from each of the liquid crystal panels are projected onto the surface of a screen so that their polarization directions differ from each other. Then, the projected linearly polarized lights pass through the screen after transforming into circularly polarized lights by transformation means provided in the screen. Thereby, the circularly polarized image lights may be transmitted to the observers without degrading the polarization characteristics by the optical systems such as lenses and screen. 
     In the concrete, the transformation means is a quarter wavelength plate and the projecting means projects each of the linearly polarized image lights onto the screen so that the polarization axis of the image lights make an angle of 45° with an optical axis of the quarter wavelength plate. At this time, it is preferable to dispose the quarter wavelength plate on the back of the screen so that the image light which has transmitted from the front (light source side) surface of the screen in the linearly polarized state reaches to an observer after transforming into the circularly polarized light at the back of the screen. 
     Further, according to the present invention, the observer can enjoy to select various modes by switching them by one display unit from either a first mode which allows images to be displayed stereoscopically, a second mode which allows different observers to observe different images and a third mode for superimposing and displaying the same images. 
     In the concrete, the display unit of the present invention comprises a first liquid crystal panel for displaying images and a second liquid crystal panel for displaying images disposed adjacent to the first liquid crystal panel. And the linearly polarized image lights outputs are projected from the first and second liquid crystal panels, respectively, on the light source side surface of the screen simultaneously so that their polarization directions differ from each other. Then, transformation means provided in the screen transforms the projected linearly polarized lights into circularly polarized lights. 
     This transformation means is a quarter wavelength plate and the projecting means projects each of the linearly polarized image lights onto the screen so that the polarization axis of the image lights make an angle of 45° with an optical axis of the quarter wavelength plate. At this time, it is preferable to dispose the quarter wavelength plate on the back of the screen so that the image light which has transmitted from the light source side surface of the screen in the linearly polarized state reaches to an observer after transforming into the circularly polarized light. 
     In the present invention, the quarter wavelength plate is provided within the screen itself, because the polarization characteristics of the image light in passing through the screen degrade by scattering and the like. Thus failing to view stereoscopic images or causing after-image or darkness if the quarter wavelength plate is separated from the screen and is disposed in front of the screen (on the light source side). It is particularly difficult to let the image light pass through the screen while maintaining the polarization characteristics when circularly polarized light is used. Then, the quarter wavelength plate is provided within the screen itself to allow the circularly polarized image light to be transmitted to the observer without degrading the polarization characteristics by the optical systems such as the lenses and screen. 
     Further, it is preferable to construct the projecting means described above by combining a plurality of polarization plates. In concrete, the projecting means is constructed by combining a first polarization plate disposed on the light source side of the first liquid crystal panel; a second polarization plate which is disposed on the screen side of the first liquid crystal panel and whose polarization direction makes an angel of 90° with that of the first polarization plate; a third polarization plate disposed on the light source side of the second liquid crystal panel; and a fourth polarization plate which is disposed on the screen side of the second liquid crystal panel and whose polarization direction makes an angle of 90° with that of the third polarization plate. It is noted that the orientation of liquid crystal of the first and second liquid crystal panels is different by 90° from each other. 
     It is preferable to provide the screen with, besides the quarter wavelength plate, an image-formation film for forming images; a Fresnel lens provided on the light source side toward the image-formation film; and a lenticular lens provided on the observer side with respect to the image-formation film. 
     Further, in a display system of the present invention, an observer watches images from the back of the screen by wearing special glasses. The glasses have a function of selectively separating the image lights for right and left eyes, respectively from the first and second liquid crystal panels which have passed the screen. Thereby, it allows stereoscopic images to be observed. 
     In the concrete, circularly polarizing means by which directions of rotation of circularly polarized light differ each other for the right eye and left eye and linearly polarizing means by which polarization directions of linearly polarized lights differ each other for the right eye and left eye are provided respectively in the glasses. The combination of the circularly polarizing means and the linearly polarizing means allows the image which has passed through the screen to be observed. 
     Further, the inventive display system allows different images to be observed among a first observer and a second observer. In this case, different glasses are allotted to the first and second observers, respectively. In the concrete, first glasses is selectively transmitting the image light of the first liquid crystal panel and second glasses id selectively transmitting the image light of the second liquid crystal panel to the second observer, respectively. Here, in the first and second glasses, circularly polarizing means for different directions of rotation of circularly polarized lights differ each other and linearly polarizing means by which polarization directions of linearly polarized lights differ each other are provided. 
     Further, in the inventive display system, the same images are displayed respectively on the first and second liquid crystal panels and the same images are superimposed and displayed on the screen, simultaneously. Thereby, the observer can see the image without wearing the special glasses. Even more, the brightness of the image is doubled as compared to a case when one liquid crystal panel is used. Images of TV, VTR, personal computer (PC) and the like are conceivable for example as such images. Moreover, the apparent resolution of the image may be enhanced by projecting the same images to the screen simultaneously while shifting either image of the first or second liquid crystal panel in the horizontal or vertical direction by a length of a pixel. For example, if the image from the second liquid crystal panel is projected to the screen so as to cover the space between the first image pixels which are adjacent vertically, the vertically resolution of a whole image increases twice. While they are the same images, it is also possible to enhance an angle of visibility because left or right turn circularly polarized image light is used. 
     In the inventive display unit, it is possible to select various operation modes by one display unit. That is, it is possible to select either a first mode which allows images to be displayed stereoscopically, a second mode which allows different images to be observed among different observers, respectively, and a third mode for superimposing and displaying the same images. 
     In the concrete, the observer selects a desirable mode by mode selection means at first. When the first mode for displaying images stereoscopically is selected, display control means causes the images for right and left eyes to be displayed on the first and second liquid crystal panels, respectively, by the stereoscopic display control means. 
     When the second mode which different images are observed among different observers is selected, the display control means causes desired different images from the input means in order to display the different images on the first and second liquid crystal panels respectively. 
     When the third mode for superimposing and displaying the same images is selected, the display control means causes the same images t from the input means in order to display on the first and second liquid crystal panels simultaneously. Thus, it becomes possible to display multipurpose images by one display unit. 
     The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the description and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic view showing an optical system of a display unit of the present invention; 
     FIG. 2 is a time chart in displaying stereoscopic images (first mode); 
     FIG. 3 is a time chart in displaying different images (second mode); 
     FIG. 4 is a circuit diagram for displaying multi-purpose images; 
     FIGS. 5A,  5 B and  5 C are drawings showing a structure of a screen; 
     FIGS. 6A,  6 B and  6 C are drawings showing another structure of the screen; 
     FIGS. 7A,  7 B and  7 C are drawings showing a still other structure of the screen; 
     FIG. 8 is a diagram showing a structure of a liquid crystal panel; 
     FIGS. 9A,  9 B and  9 C are a diagram showing a concrete structure of the display unit; 
     FIG. 10 is a detailed diagram showing an optical structure of the display unit in FIG. 9; 
     FIG. 11 is a diagram showing another structure of a liquid crystal panel; and 
     FIGS. 12A-12C are a diagram showing a concrete structure of the display unit. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a preferred embodiment of an optical system of a display unit of the present invention. The inventive display unit is of the so-called rear projection method which allows an image to be observed from the back of a screen, i.e. on the opposite side from a light source, by forming the image on the surface of the screen via the light source. Polarization plates  3   a ,  3   b ,  5   a , and  5   b , liquid crystal panels  4   a  and  4   b , and lenses  6   a  and  6   b  for displaying images are disposed respectively at right and left between the light source  1  and the screen  2 . In the concrete, the polarization plate  3   a , the liquid crystal panel  4   a , the polarization plate  5   a  and the lens  6   a  are disposed respectively in the order from the light source side in the right optical system and the polarization plate  3   b , the liquid crystal panel  4   b , the polarization plate  5   b  and the lens  6   b  are disposed respectively in the order from the light source side in the left optical system. 
     The polarization plates  3   a  and  3   b  have polarization directions as indicated by solid line arrows (which make an angle of 90° each other). The polarization plates  5   a  and  5   b  also have polarization directions as indicated by solid line arrows (which make an angle of 90° each other). Meanwhile, each of the liquid crystal panels  4   a  and  4   b  has orientations as indicated by dot lines (differ by 90° from each other). The screen  2  is composed of an image-formation film  20 , an acryl  21  and a quarter wavelength film  22  (or quarter wavelength plate). The quarter wavelength film  22  transforms linearly polarized light into circularly polarized light. 
     In the system constructed as described above, each of linearly polarized image lights output respectively from the liquid crystal panels  4   a  and  4   b  is projected simultaneously onto the surface of the screen  2  via the right or left optical systems such that their polarization directions differ by 45° with respect to an optical axis of the quarter wavelength film  22 . Then, the projected linearly polarized lights are transformed into circularly polarized light by the quarter wavelength film  22  provided in the screen  2 . The quarter wavelength film  22  is disposed on the back of the screen  2  and transforms the image lights which have transmitted from the light source side surface of the screen  2  in the state of linearly polarized light into the circularly polarized light at the back of the screen  2 . 
     An operation of the present embodiment will be explained below. At first, an operation in observing a stereoscopic image will be explained. 
     Assuming here that the liquid crystal panels  4   a  and  4   b  display images for left eye and right eye, respectively, an observer observes those images by wearing special glasses  7  from the back of the screen  2 . The glasses  7  have a function of selectively separating the image lights of the liquid crystal panels  4   a  and  4   b  which have passed through the screen  2  for the left eye and for the right eye. In the concrete, the glasses  7  are provided with circularly polarizing films whose directions of rotation of the circularly polarized lights are different from each other for the left eye  7   a  and the right eye  7   b , respectively (e.g. a left turn circularly polarizing film is used for the right eye and a right turn circularly polarizing film is used for the left eye). And the glasses are also having linearly polarizing films whose optical axis of linearly polarized lights make an angle of 45° with the optical axis of the circularly polarizing film, respectively. 
     Two linearly polarized images having polarization directions indicated by arrows X and Y in FIG. 1 (which make an angel of 45° with an optical axis Z of the quarter wavelength film  22 , respectively, and which make an angle of 90° each other) are superimposed and displayed on the screen  2 . These linearly polarized images pass through the screen  2  while being transformed, by the quarter wavelength film  22 , into the circularly polarized lights whose directions of rotation differ from each other. The image lights which have thus passed the screen  2  are selectively separated by the glasses  7  having the glass for left eye  7   a  and the glass for right eye  7   b . That is, for the observer wearing the glasses  7 , the image formed in the liquid crystal panel  4   a  enters the left eye and the image formed in the liquid crystal panel  4   b  enters the right eye selectively. Thus, the observer wearing the glasses  7  can see a stereoscopic image selectively. 
     This operation will be explained with reference to a time chart in FIG.  2 . 
     Image data of AL 0 , AL 1 , AL 2 , AL 3 , AL 4 , . . . , i.e. images for the left eye, are displayed from the liquid crystal panel  4   a  and image data of AR 0 , AR 1 , AR 2 , AR 3 , AR 4 , . . . , i.e. images for the right eye, are displayed from the liquid crystal panel  4   b . Then, the images of AL 0 , AL 1 , AL 2 , AL 3 , AL 4 , . . . enter the left eye and the images of AR 0 , AR 1 , AR 2 , AR 3 , AR 4 , . . . enter the right eye selectively by wearing the glasses  7 . It becomes possible to observe the stereoscopic image by wearing the glasses  7  having the circularly polarizing films and the linearly polarizing films, without being influenced by an inclination of the observer&#39;s head. 
     Next, an operation of second mode for causing a first observer and a second observer to observe different images will be explained. Different images are displayed by the liquid crystal panels  4   a  and  4   b , respectively, and the first and second observers watch the different images from the back of the screen  2  by wearing special glasses  70   a  and  70   b , respectively. At this time, the first observer wears the glasses  70   a  which selectively separates the image light of the liquid crystal panel  4   a  and the second observer wears the glasses  70   b  which selectively separates the image light of the liquid crystal panel  4   b  from the displayed image. Here, the glasses  70   a  and  70   b  are provided with circularly polarizing films whose directions of rotation of the circularly polarized lights are different from each other and linearly polarizing films whose optical axis of linearly polarized lights make an angle of 45° with the optical axis of the circularly polarizing film, respectively. 
     Linearly polarized images which have been formed by being optically modulated by the liquid crystal panels  4   a  and  4   b  are superimposed and displayed on the screen  2  via the lenses  6   a  and  6   b . Their polarization directions are indicated by arrows X and Y in FIG. 1 (which make an angle of 45° with an optical axis Z of the quarter wavelength film  22 , respectively). That is, the image which has been formed on the liquid crystal panel  4   a  is simultaneously projected onto the screen  2  as having the linearly polarized direction indicated by the arrow X and the image which has been formed on the liquid crystal panel  4   b  is projected onto the screen  2  as having the linearly polarized direction indicated by the arrow Y. 
     These linearly polarized images pass through the screen  2  while being transformed by the quarter wavelength film  22  into circularly polarized lights A and B whose directions of rotation differ from each other. The image lights which have thus passed the screen  2  are selectively separated by the glasses  70   a  and  70   b  which have different polarization directions. That is, the image formed on the liquid crystal panel  4   a  enters the eyes of the observer wearing the glasses  70   a  and the image formed on the liquid crystal panel  4   b  enters the eyes of the observer wearing the glasses  70   b , selectively. Thus, the observers wearing the different glasses  70   a  and  70   b  can selectively see different images. 
     If one sees the screen  2  without the special glasses at this time, two images overlap because human eyes are incapable of discriminating the polarization. However, it becomes possible to separate and to see those two images selectively by viewing the screen  2  by wearing the special glasses  70   a  and  70   b  comprising the circularly polarizing films and the linearly polarizing films. 
     That is, the image formed on the liquid crystal panel  4   a  can be seen selectively by the glasses  70   a  because it has circularly polarized light in the direction of rotation indicated by the arrow A. At this time, the image formed on the liquid crystal panel  4   b  cannot be seen by the glasses  70   a  because it has circularly polarized light in the direction of rotation indicated by the arrow B. 
     On the other hand, the image formed on the liquid crystal panel  4   b  can be seen selectively by the glasses  70   b  because it has the circularly polarized light in the direction of rotation indicated by the arrow B. At this time, the image formed on the liquid crystal panel  4   a  cannot be seen by the glasses  70   b  because it has the circularly polarized light in the direction of rotation indicated by the arrow A. 
     This operation will be explained with reference to a time chart in FIG.  3 . 
     Image data of A 0 , A 1 , A 2 , A 3 , . . . are displayed from the liquid crystal panel  4   a  and image data of B 0 , B 1 , B 2 , B 3 , B 4 , . . . are displayed from the liquid crystal panel  4   b . Then, the images of A 0 , A 1 , A 2 , A 3 , . . . enter the eyes of the first observer wearing the glasses  70   a  and the images of B 0 , B 1 , B 2 , B 3 , B 4 , . . . enter the eyes of the second observer wearing the glasses  70   b  selectively by wearing the special glasses described above. It becomes possible to observe the different images among the first and second observers without being influenced by inclinations of their head. 
     Next, an operation for the third mode in displaying normal images of TV, VTR, personal computers (PC) and the like will be explained. In this case, the same images are displayed from the liquid crystal panels  4   a  and  4   b . Thereby, the observer can see brighter images without wearing the special glasses. At this time, an apparent resolution may be enhanced by projecting the same images simultaneously on the screen  2  while shifting either one of the images of the liquid crystal panels  4   a  and  4   b  in the horizontal or vertical direction by length of a pixel. For example, Further, although these images are the same images, an angle of visibility may be improved because right and left turn circularly polarized image lights are used. 
     Next, a structure of a circuit of a multi-purpose image display unit which allows to select various operation modes by one display unit will be explained with reference to FIG.  4 . Here, the operation modes includes a first mode which allows to display stereoscopic images, a second mode which allows different observers to observe different images and a third mode for superimposing and displaying the same image. 
     The liquid crystal panel  4   a  is connected with an image control circuit  8   a  and an image selection circuit  9   a . On the other hand, the liquid crystal panel  4   b  is connected with an image control circuit  8   b  and an image selection circuit  9   b . The image control circuits  9   a  and  9   b  are connected with TV tuners  10   a  and  10   b  and external sound and image interfaces  11   a  and  11   b , respectively. The external sound and image interface  11   a  is connected with a video tape recorder  12  and the external sound and image interface  11   b  is connected with a game machine  13 . The image control circuit  8   a  and  8   b  and the image selection circuits  9   a  and  9   b  are connected to a display system control unit  14 . 
     A timing generator  15  and a stereoscopic display control circuit  16  are connected respectively to the display system control unit  14 . The timing generator  15  is connected also to a stereoscopic display control circuit  16  and to the image control circuits  8   a  and  8   b , respectively. The TV tuners  10   a  and  10   b  and the external sound and image interfaces  11   a  and  11   b  are also connected a sound selection circuit  17  which is in turn connected to the display system control unit  14 . Desirable sound is output from a speaker  18  by this sound selection circuit  17 . 
     The timing generator  15  generates the reference timing of the system and the image control circuits  8   a  and  8   b , the display system control unit  14  and the stereoscopic display control circuit  16  operate in synchronism with its reference signal. The display system control unit  14  controls and monitors status of the systems such as instruction to the image selection circuits  9   a  and  9   b  for selecting images, instruction to selecting sound selection circuit  17  for selecting sounds, instruction for operation modes to the image control circuits  8   a  and  8   b , and processing for interruption from the image control circuits  8   a  and.  8   b  and peripheral sensors (not shown). 
     The image selection circuits  9   a  and  9   b  select images input from the TV tuners  10   a ,  10   b , and the outside. The image control circuits  8   a  and  8   b  adjust hue, brightness and contrast and the like. Besides that, the image control circuits  8   a  and  8   b  generate control signals such as image signals, timing signals and the like for the liquid crystal panels  4   a  and  4   b . The sound selection circuit  17  selects an optional sound, outputs from the speaker  18  and controls sound volume and sound quality. 
     An operation of the circuit of the multi-purpose image display unit will be explained per each operation mode. 
     At first, a case of displaying a stereoscopic image will be explained (first mode). 
     In this case, the display system control unit  14  sets up hardware necessary for the first operation mode in response to the instruction of selecting the stereoscopic image set from the outside and selects image and sound effectively from the stereoscopic display control circuit  16 . An image for right eye (R-image) and an image for left eye (L-image) are output from the stereoscopic display control circuit  16  in synchronism in parallel. Then, the image for left eye (L-image) is output and displayed on the liquid crystal panel  4   a  via the image selection circuit  9   a  and the image control circuit  8   a . Meanwhile, the image for right eye (R-image) is output and displayed on the liquid crystal panel  4   b  via the image selection circuit  9   b  and the image control circuit  8   b . Thus, the image for left eye and the image for right eye are output from the liquid crystal panels  4   a  and  4   b  and are projected onto the screen  2  in synchronism. 
     Next, the case of observing different images among different observers will be explained (second mode). Here, it will be explained by exemplifying a case of displaying an image of the video tape recorder and an image of the game machine onto the screen in the same time and of observing them among the different observers. 
     At first, in response to the instruction of the second mode, the display system control unit  14  selects the external sound and image interface  11   a  by the image selection circuit  9   a  and selects the external sound and image interface  11   b  by the image selection circuit  9   b . Thereby, image data of the video tape recorder  12  is output and displayed on the liquid crystal panel  4   a  via the image selection circuit  9   a  and the image control circuit  8   a . Meanwhile, image data of the game machine  13  is output and displayed on the liquid crystal panel  4   b  via the image selection circuit  9   b  and the image control circuit  8   b . Thereby, the different images are output from the liquid crystal panels  4   a  and  4   b  and projected onto the screen  2  simultaneously. 
     Next, the case of superimposing and displaying the same images will be explained by exemplifying a case of superimposing and displaying images of the TV tuner  10   a  on the screen  2 . 
     At first, in response to the instruction of the third mode, the display system control unit  14  selects the TV tuner  10   a  by the image selection circuits  9   a  and  9   b . Thereby, an image of the TV tuner  10   a  is output to the liquid crystal panel  4   a  via the image selection circuit  9   a  and  8   a . Further, the same image is output to the liquid crystal panel  4   b  via the image selection circuit  9   b  and the image control circuit  8   b . Thereby, the same images are output from the liquid crystal panels  4   a  and  4   b  and are projected onto the screen  2  simultaneously. 
     Here, the selection of the operation modes described above is carried out by means of a mode change-over switch  14   a  for selecting the operation modes. Then, the display system control unit  14  outputs the selection instruction in response to a selection signal from the mode change-over switch  14   a.    
     Next, the structure of the screen  2  used in the inventive display unit will be explained with reference to FIGS. 5A,  5 B and  5 C. Here, FIG. 5A is a section view thereof, FIG. 5B is a plan view thereof and FIG. 5C shows the optical axis of the quarter wavelength plate, respectively. In the present embodiment, the screen  2  is composed of, in the order from the light source side, a fresnel lens  23 , an image-formation film  20 , a lenticular lens  24  and the quarter wavelength film  22 . In the present invention, the quarter wavelength film  22  is provided in a body with the screen  2  itself. It is because the polarization characteristics of the image light degrade due to scattering and the like in passing through the screen if the quarter wavelength film  22  is separated from the screen  2  and is disposed in front of the screen  2  (on the light source side), thus failing to view the image stereoscopically or causing after-image or darkness. The optical axis of the quarter wavelength film  22  (dotted line in FIG. 5C) is set at an angle of ±45° with vertical stripe of the lenticular lens  24 . 
     Another structure of the screen used in the inventive display unit will be explained below with reference to FIGS. 6A,  6 B and  6 C. Here, FIG. 6A is a section view thereof, FIG. 6B is a plan view thereof and FIG. 6C shows the optical axis of the quarter wavelength plate, respectively. 
     In the present embodiment, the screen  2  is composed of, in the order from the side of the light source, the fresnel lens  23 , the image-formation film  20 , the lenticular lens  24  and the quarter wavelength film  22 . Then, the quarter wavelength film  22  is provided along the surface of the lenticular lens  24 . The optical axis of the quarter wavelength film  22  (dotted line in FIG. 6C) is set at an angle of ±45° with vertical stripe of the lenticular lens  24 . An incidence phase of image light through the lenticular lens  24  makes an angle of ±45° with respect to the optical axis of the quarter wavelength film  22 . 
     A still other structure of the screen used in the inventive display unit will be explained below with reference to FIGS. 7A,  7 B and  7 C. Here, FIG. 7A is a section view thereof, FIG. 7B is a plan view thereof and FIG. 7C shows the optical axis of the quarter wavelength plate, respectively. In the present embodiment, the screen  2  is composed of, in the order from the side of the light source, the fresnel lens  23 , the image-formation film  20 , the quarter wavelength film  22  and the lenticular lens  24 . The image-formation film  20  and the quarter wavelength film  22  are disposed so as to contact each other. In the present embodiment, the image-formation film  20  and the quarter wavelength film  22  may be disposed by switching each other. The optical axis of the quarter wavelength film  22  (dotted line in FIG. 7C) is set at an angle of ±45° with respect to vertical fringes of the lenticular lens  24 . 
     Next, the liquid crystal panels  4   a  and  4   b  used in the present invention will be explained with reference to FIG.  8 . At first, in the structure at least one active matrix area and peripheral circuit areas are integrated on the same substrate. In this case, each active matrix area corresponds to each of the liquid crystal panels  4   a  and  4   b  in FIG.  1 . 
     The integrated liquid crystal panel is characterized in that the peripheral circuits are disposed commonly to the plurality of active matrix areas. Thereby, the structure may be simplified and the reliability of the unit itself may be enhanced. Further, it allows to lower the production cost. 
     The structure of the liquid crystal panel  4  is explained below with reference to FIG.  8 . 
     The liquid crystal panel  4  is constructed by integrating an active matrix area  104 , a vertical scan control circuit  203  for driving the active matrix area  104  and a horizontal scan control circuit  201  for driving the active matrix area  104  on the same glass substrate or quartz substrate. 
     In displaying in color, three liquid crystal panels constructed as described above corresponding to R, G, B are prepared and combinations of those three liquid crystal panels are disposed in the right and left optical systems in FIG. 1, respectively. Accordingly, six liquid crystal panels as shown in FIG. 8 are necessary in total (e.g. FIG. 11) in order to construct the display unit as shown in FIG.  1 . 
     Each of the active matrix area  104 , the image-formation film  201  and the image-formation film  203  are formed as thin films directly integrated on the glass substrate or quartz substrate. In the concrete, they are formed from thin film transistors by using thin film silicon semiconductors having crystalinity. 
     Further, although not clear from the figure, a rubbing direction of an orientation film for orienting the liquid crystal is set so that it makes an angel or just 90° with a rubbing direction of an orientation film of the active matrix area  104  of the adjoining liquid crystal panel in the structure shown in FIG. 8 (see FIG.  1 ). 
     In the present embodiment, the structure described above is realized by using TN type liquid crystal. This structure makes polarization directions of the images formed in active matrix areas an angel of 90° each other. 
     It is noted that the rubbing direction in the present specification means to be an orientation as a whole. That is, in a case of an orientation in which the orientation changes subtly in a very small area, the orientation is defined by a direction which orients the liquid crystal as a whole, taking no account with very small area which changes the orientation subtly. 
     An method for operating the liquid crystal panel integrated as shown in FIG. 8, particularly, an operation of the active matrix area  104  is explained briefly below. It is noted that the similar operation is carried out in the same timing in the other active matrix areas. 
     In FIG. 8, each of flip-flop circuits  211 ,  216 ,  212 ,  213  is a circuit which can assume two stable states. Consider a case when a level of an input (at point X 1 ) of the flip-flop circuit  216  is H (logically High level) and that of an output (at point X 2 ) thereof is L (logically Low level) for example. When a rising edge of CLKH (operation clock of the horizontal scan control circuit) is input here, the output thereof turns to H level. That is, the point X 2  turns to H level. Then, this state is maintained unless a next CLKH rising edge is input. 
     Further, consider a case when the state of the input of the flip-flop circuit  216  is L and the output thereof is H for example. When the rising edge of the CLKH is input here, the output thereof turns to L level. 
     Further, consider a case when the states of the input and the output of the flip-flop circuit  216  are both L. When the rising edge of CLKH is input at this time, the output is maintained at the L level. 
     At first, the rising edge of the CLKV (operation clock of the vertical scan control circuit) is input to the flip-flop circuit  212  of the vertical scan control circuit  203 . Here, VSTA (vertical scan timing enable signal) is blanked out by the CLKV. 
     That is, the output of the flip-flop circuit  212  turns to H level when the rising edge of the CLKV enters the flip-flop circuit  212  in the state wherein the H level signal of the VSTA is applied to the input of the flip-flop circuit  212 . As a result, a signal level on a line Y 1  turns to H level. 
     When the signal level of the line Y 1  turns to H level, thin film transistors of each of pixels indicated respectively by addresses ( 1 ,  1 ), ( 2 ,  1 ), . . . (i,  1 ) are all turned ON. 
     In this state, HSTA (horizontal scan timing enable signal) to be input is blanked out in the flip-flop circuit  216  at the rising edge of CLKH (operation clock of the horizontal scan control circuit). As a result, the signal level in X 1  turns to H. 
     Because inputs of the flip-flop circuits on and after the flip-flop circuit  216  are all on L level in the stage when the CLKH described above is input, the output of the flip-flop circuits on and after the flip-flop circuit  216  are all on L level in this state. 
     Then an image sampling signal line  218  turns to H level. As a result, image data VA is taken in at a sample and hold circuit  214 . Then, a signal corresponding to predetermined image data flows through an image signal line  219 . That is, predetermined image signals are applied to thin film transistors of each pixel indicated by addresses ( 1 ,  1 ), ( 1 ,  2 ), . . . ( 1 , j). 
     In this state, the thin film transistors of each pixel indicated by the addresses ( 1 ,  1 ), ( 2 ,  1 ), . . . (i,  1 ) are all turned ON. Accordingly, image information is written only to the pixel at the address ( 1 ,  1 ). 
     Next, the output of the flip-flop circuit  211  turns to L level by the next rising edge of the CLKH. The output of the flip-flop circuit  216  also turns to H level. Thus, the level of the point X 2  turns to H. In this state, points indicated by Xi other than X 2  are all on L level. 
     As a result, predetermined image data is taken in at a sample and hold circuit  215  and information is written to the address ( 2 ,  1 ). 
     Thus, information is written up to the address (i,  1 ) sequentially in accordance to the clock signal of the CLKH. 
     When the information has been written to the line Y 1 , the output of the flip-flop circuit  212  turns to L level and the output of the flip-flop circuit  213  turns to H level by input of a next rising edge of the CLKV. 
     Information is written thus to the line Y 2 . Information is written sequentially to each pixel and when information is written finally to the address (i, j), display of one frame (or one field) is finished. This frame is repeated by 30 times per second for example. Images are thus displayed. 
     Next, a concrete structure of the display unit having the optical system described above is explained with reference to FIGS. 9A to  9 C. 
     In FIGS. 9A to  9 C, liquid crystal panel  405  has the active matrix area  104  as shown in FIG.  8 . In the FIGS. 9A to  9 C, light from a light source  401  is reflected by a mirror  402  and is reflected and divided into two beams by a half mirror  403  and a mirror  404 . These beams enter each liquid crystal panel  405  and are optically modulated in a predetermined manner. 
     Two images obtained by optically modulating at each liquid crystal panel  405  are projected respectively via an optical system  406 . 
     The projected light from the optical system  406  is reflected by a mirror  407  and is projected onto a screen  408 . The two images optically modulated at the liquid crystal panels  405  are superimposed and projected on the screen  408 . Here, the polarization of the two images make an angle of 90° each other. 
     FIG. 10 shows a detailed structure of one of the optical systems (either one of the right and left optical systems in FIG.  1 ). Light from a light source  150  is separated into red, green and blue lights via dichroic mirrors for color separation  152   a  and  152   b  and enters a red liquid crystal panel  154   b , a green liquid crystal panel  154   c  and a blue liquid crystal panel  154   a , respectively, to be optically modulated. The image lights optically modulated by each of the liquid crystal panels  154   a ,  154   b  and  154   c  are projected onto a screen  156  by a projection lens  155  via dichroic mirrors for color synthesis  152   e  and  152   d . Here, the reference numeral ( 151 ) denotes a UV filter, ( 153   a  and  153   b ) total reflection mirrors and ( 157   a  and  157   b ) condenser lenses. 
     Another structure of the liquid crystal panel will be explained below with reference to FIG.  11 . The present embodiment is a case when a number of active matrix areas are integrated. 
     FIG. 11 shows an outline structure of the liquid crystal panel in which the active matrix areas are integrated. This liquid crystal panel shown in FIG. 11 is capable of forming two color images composed of R, G, B independently. 
     In the structure shown in FIG. 11, horizontal scan of the active matrix areas  703 ,  704  and  705  is controlled by a horizontal scan control circuit  701 . Further, horizontal scan of the active matrix areas  706 ,  707  and  708  is controlled by a horizontal scan control circuit  702 . Each of these active matrix areas corresponds to the liquid crystal panel  4  in FIG.  1 . 
     Further, vertical scan of the active matrix areas  703  and  706  is controlled by a vertical scan control circuit  709 . Further, vertical scan of the active matrix areas  704  and  707  is controlled by a vertical scan control circuit  710 . A vertical scan control circuit  711  controls vertical scan of the active matrix areas  705  and  708 . 
     In the structure shown in FIG. 11, a rubbing direction (orientation) of orientation films disposed on the active matrix areas  703  to  705  makes an angle of 90° with a rubbing direction (orientation) of orientation films disposed on the active matrix areas  706  to  708 . 
     The above-mentioned structure may be integrated on the same substrate, thus allowing to simplify the whole structure and to lower the production cost. In particular, it is very useful to be able to dispose the horizontal scan control circuits/vertical scan control circuits commonly to the plurality of active matrix areas. 
     Next, a concrete structure of the display unit having the optical system in FIG. 11 will be explained with reference to FIGS. 12A to  12 C. In the structure shown in FIGS. 12A to  12 C light from a light source  602  is reflected by a mirror  604  and is divided by dichroic mirrors  608 ,  609  and  610  into lights having wavelength domains corresponding to G, B, R, respectively. Then, each of those lights is input to the integrated liquid crystal panel  611  shown in FIG.  11 . 
     The light is optically modulated at each pixel area corresponding to R, G, B in the liquid crystal panel  611  and an image of G is reflected by a mirror  612 , an image of B is reflected by a half mirror  613  and an image of R is reflected by a half mirror  614 . A color image thus combined is reflected further by a mirror  617  via an optical system  615  and is projected onto a screen  618 . 
     Meanwhile, light from the light source  602  is reflected by the mirror  604  and is divided into lights corresponding to GBR by dichroic mirrors  605 ,  606  and  607 . Those lights are optically modulated by a liquid crystal panel  611 . The optically modulated lights corresponding to RGB are combined by a group of mirrors not shown and are projected onto the screen  618  via an optical system  616  and the mirror  617 . 
     As described above, according to the present invention, the display unit is provided with the first and second liquid crystal panels for displaying images. And linearly polarized image lights output respectively from each of the liquid crystal panels are projected onto the surface of the screen so that their polarization directions differ from each other. Then, the projected linearly polarized lights are transmitted through the screen after transforming into circularly polarized lights by transformation means provided in the screen. Thereby, the circularly polarized image lights may be transmitted to the observers without degrading the polarization characteristics by the optical system such as the lenses and screen. 
     Further, according to the present invention, the observer can enjoy various modes by one display unit by allowing to arbitrarily select either the first mode which allows to display stereoscopic images, the second mode which allows to observe different images among different observers and the third mode for superimposing and displaying the same images.