Abstract:
A system and method to synchronize one or more shutters on user-worn headgear with a sequence of images shown on a display by initially synchronizing the shutter(s) with the sequence of images using an initial synchronization signal generated externally to the headgear and by maintaining synchronization of the shutter(s) with the sequence of images using an ongoing synchronization signal generated independently by the headgear.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60/182,979, filed Feb. 16, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The instant invention relates to a system and method to synchronize one or more shutters with a sequence of images.  
           [0004]    More particularly, the instant invention relates to a system and method to synchronize one or more shutters on user-worn headgear with a sequence of images shown on a display by initially synchronizing the shutter(s) with the sequence of images using an initial synchronization signal generated externally to the headgear and by maintaining synchronization of the shutter(s) with the sequence of images using an ongoing synchronization signal generated independently by the headgear.  
           [0005]    2. Description of the Related Art  
           [0006]    Stereoscopic 3-D viewing systems for video games, computer graphics, movies, and the like are well known. In summary, they operate by showing a sequence of interlaced right-eye images and left-eye images on a display, by closing a right-eye shutter to block a viewer&#39;s view of the display when a left-eye image is shown, and by closing a left-eye shutter to block the viewer&#39;s view of the display when a right-eye image is show.  
           [0007]    More particularly, as seen in the prior art system of FIG. 1, Control Unit  101  (which may be computer, a video game, or a movie projector) includes Image Generator  103 , which provides a sequence of images to Display  105 . The sequence of images is composed of a sequence of interlaced right-eye images and left-eye images. Synchronizing Circuit  107 , which controls the timing of the images generated by Image Generator  103 , also provides an Ongoing Synchronization Signal  109   a  to Infrared Transmitter  111  through Connection  112 . The Ongoing Synchronization Signal  109   a , which is transmitted in infrared form as Ongoing Synchronization Signal  109   b  to Infrared Detector  113  of 3-D Glasses  115 , is used by Control Circuit  117  of 3-D Glasses  115  to synchronize the Right-eye Shutter  119   a  and the Left-eye shutter  119   b  of 3-D Glasses  115  with the right-eye and left-eye images shown on the display.  
           [0008]    [0008]FIG. 2 shows another prior art system which is similar to the system shown in FIG. 1 but uses a hard-wired connection to carry the Ongoing Synchronization Signal to the 3-D Glasses. More particularly, it is seen in this FIG. 2 that Control Unit  201  (which may be computer, a video game, or a movie projector) includes Image Generator  203 , which provides a sequence of images to Display  205 . The sequence of images is composed of a sequence of interlaced right-eye images and left-eye images. Synchronizing Circuit  207 , which controls the timing of the images generated by Image Generator  203 , also provides an Ongoing Synchronization Signal  209  to 3-D Glasses  213  through hard-wired link  211 . The Ongoing Synchronization Signal  209  is used by Control Circuit  215  of 3-D Glasses  213  to synchronize the Right-eye Shutter  217   a  and Left-eye Shutter  217   b  of 3-D Glasses  213  with the right-eye and left-eye images shown on the display.  
           [0009]    Such prior art systems suffer a number of disadvantages. With regard to the system of FIG. 1, which employs the wireless delivery of the Ongoing Synchronization Signal, the use of a wireless transmitter such as an infrared transmitter increases the cost of the system. With regard to the system of FIG. 2, which employs the hard-wired delivery of the Ongoing Synchronization Signal, the wire connecting the 3-D Glasses to the Control Unit restricts movement and is clearly inconvenient to the viewer.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of the present invention to provide a system and method to synchronize one or more shutters on user-worn headgear with a sequence of images shown on a display by initially synchronizing the shutter(s) with the sequence of images using an initial synchronization signal generated externally to the headgear and by maintaining synchronization of the shutter(s) with the sequence of images using an ongoing synchronization signal generated independently by the headgear. The initial synchronization signal generated externally to the headgear may be transmitted to the headgear through a hard-wired link which may be broken after the transmission of the initial synchronization signal. Alternatively, the initial synchronization signal generated externally to the headgear may be transmitted (preferably as visible light) to the headgear from the display upon which the sequence of images is shown.  
           [0011]    Thus, the system and method of the instant invention eliminate the need for a continuous hard-wired connection to transmit an ongoing synchronization signal to the headgear. The system and method of the instant invention also eliminate the need to use a dedicated wireless transmitter to transmit an ongoing synchronization signal to the headgear.  
           [0012]    Other objects and advantages will become apparent from the detailed description, claims, and accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a block diagram of a prior art stereoscopic viewing system;  
         [0014]    [0014]FIG. 2 shows a block diagram of another prior art stereoscopic viewing system;  
         [0015]    [0015]FIG. 3 shows a block diagram of a first embodiment of the present invention;  
         [0016]    [0016]FIG. 4 shows a flowchart describing the operation of the first embodiment of the present invention;  
         [0017]    [0017]FIG. 5 shows a block diagram of a second embodiment of the present invention;  
         [0018]    [0018]FIG. 6 shows a flowchart describing the operation of the second embodiment of the present invention;  
         [0019]    [0019]FIG. 7 shows a block diagram of a third embodiment of the present invention;  
         [0020]    [0020]FIG. 8 shows a flowchart describing the operation of the third embodiment of the present invention;  
         [0021]    [0021]FIG. 9 shows a block diagram of a fourth embodiment of the present invention;  
         [0022]    [0022]FIG. 10 shows a flowchart describing the operation of the fourth embodiment of the present invention;  
         [0023]    [0023]FIG. 11 shows a block diagram of a fifth embodiment of the present invention;  
         [0024]    [0024]FIG. 12 shows a flowchart describing the operation of the fifth embodiment of the present invention;  
         [0025]    [0025]FIG. 13 shows a block diagram of a sixth embodiment of the present invention; and  
         [0026]    [0026]FIG. 14 shows a flowchart describing the operation of the sixth embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    A system for cycling a right-eye shutter between a substantially transparent state and a substantially opaque state in substantial synchronism with a right-eye sequence of images shown on a display and for cycling a left-eye shutter between a substantially opaque state and a substantially transparent state in substantial synchronism with a left-eye sequence of images shown on the display is provided, comprising cycling means for cycling the right-eye shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency and for cycling the left-eye shutter between the substantially transparent state and the substantially opaque state at the predetermined frequency; and synchronization means for synchronizing the cycling means with the image sequences shown on the display by detecting at least one synchronization image displayed on the display.  
         [0028]    A system for cycling a right-eye shutter of a shutter system between a substantially transparent state and a substantially opaque state in substantial synchronism with a right-eye sequence of images generated by a control unit external to the shutter system and for cycling a left-eye shutter of the shutter system between a substantially opaque state and a substantially transparent state in substantial synchronism with a left-eye sequence of images generated by the control unit is provided, comprising cycling means for cycling the right-eye shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency and for cycling the left-eye shutter between the substantially transparent state and the substantially opaque state at the predetermined frequency; and synchronization means for synchronizing the cycling means with the image sequences shown on the display by detecting a synchronization signal provided by the control means via a breakable hard-wired connection.  
         [0029]    A system for cycling a shutter between a substantially transparent state and a substantially opaque state in substantial synchronism with a sequence of images shown on a display is provided, comprising cycling means for cycling the shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; and synchronization means for synchronizing the cycling means with the sequence of images shown on the display by detecting at least one synchronization image displayed on the display.  
         [0030]    A system for cycling a shutter of a shutter system between a substantially transparent state and a substantially opaque state in substantial synchronism with a sequence of images generated by a control unit external to the shutter system is provided, comprising cycling means for cycling the shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; and synchronization means for synchronizing the cycling means with the image sequences shown on the display by detecting a synchronization signal provided by the control means via a breakable hard-wired connection.  
         [0031]    The right-eye image sequence and the left-eye image sequence may be displayed on the display in a time-multiplexed fashion, wherein the cycling means places the right-eye shutter in the substantially transparent state and the left-eye shutter in the substantially opaque state when the right-eye image sequence is displayed and wherein the cycling means places the right-eye shutter in the substantially opaque state and the left-eye shutter in the substantially transparent state when the left-eye image is displayed. The cycling means may cycle the right eye shutter and the left-eye shutter in phases substantially  180  degrees apart from one another. The right-eye shutter and the left-eye shutter may be liquid crystal shutters. The predetermined frequency at which the right-eye shutter and left-eye shutter are cycled may substantially match or be a multiple of a refresh frequency of the display. The synchronization means may include a light-sensitive element for detecting the at least one synchronization image displayed on the display. The shutter system may be a head-mounted shutter system.  
         [0032]    A method for cycling a right-eye shutter between a substantially transparent state and a substantially opaque state in substantial synchronism with a right-eye sequence of images shown on a display and for cycling a left-eye shutter between a substantially opaque state and a substantially transparent state in substantial synchronism with a left-eye sequence of images shown on the display is provided, comprising cycling the right-eye shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; cycling the left-eye shutter between the substantially transparent state and the substantially opaque state at the predetermined frequency; and synchronizing the cycling of the right-eye shutter and the left-eye shutter with the image sequences shown on the display by detecting at least one synchronization image displayed on the display.  
         [0033]    A method for cycling a right-eye shutter of a shutter system between a substantially transparent state and a substantially opaque state in substantial synchronism with a right-eye sequence of images generated by a control unit external to the shutter system and for cycling a left-eye shutter of the shutter system between a substantially opaque state and a substantially transparent state in substantial synchronism with a left-eye sequence of images generated by the control unit is provided, comprising cycling the right-eye shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; cycling the left-eye shutter between the substantially transparent state and the substantially opaque state at the predetermined frequency; and synchronizing the cycling of the right-eye shutter and left-eye shutter with the image sequences shown on the display by detecting a synchronization signal provided by the control means via a breakable hard-wired connection.  
         [0034]    A method for cycling a shutter between a substantially transparent state and a substantially opaque state in substantial synchronism with a sequence of images shown on a display is provided, comprising cycling the shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; and synchronizing the cycling of the shutter with the sequence of images shown on the display by detecting at least one synchronization image displayed on the display.  
         [0035]    A method for cycling a shutter of a shutter system between a substantially transparent state and a substantially opaque state in substantial synchronism with a sequence of images generated by a control unit external to the shutter system is provided, comprising cycling the shutter between the substantially transparent state and the substantially opaque state at a predetermined frequency; and synchronizing the cycling of the shutter with the image sequences shown on the display by detecting a synchronization signal provided by the control means via a breakable hard-wired connection.  
         [0036]    The right-eye image sequence and the left-eye image sequence may be displayed on the display in a time-multiplexed fashion, wherein the right-eye shutter is placed in the substantially transparent state and the left-eye shutter in the substantially opaque state when the right-eye image sequence is displayed and wherein the right-eye shutter is placed in the substantially opaque state and the left-eye shutter in the substantially transparent state when the left-eye image is displayed. The right-eye shutter and the left-eye shutter may be cycled in phases substantially 180 degrees apart from one another. The right-eye shutter and the left-eye shutter may be liquid crystal shutters. The predetermined frequency at which the right-eye shutter and left-eye shutter are cycled may substantially match or be a multiple of a refresh frequency of the display. The synchronization of the cycling of the right-eye shutter and the left-eye shutter with the image sequences shown on the display may be accomplished by utilizing a light-sensitive element for detecting the at least one synchronization image displayed on the display device. The shutter system may be a head-mounted shutter system.  
         [0037]    Referring now to FIG. 3, a first embodiment of the instant invention is shown. As seen in this FIG. 3, Computer  301  (which may include input means such as a keyboard, a joystick, and a mouse, all of which are not shown) incorporates Image Generator  303  and Computer-based Synchronizer  305 . Each of Image Generator  303  and Computer-based Synchronizer  305  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a keyboard (not shown) associated with Computer  301  the Computer-based Synchronizer  305  directs Image Generator  303  to display an Initial Synchronization Sequence  309  on Display  307 . This Initial Synchronization Sequence  309  may comprise a sequence of predetermined images. Thereafter, the Image Generator  303  sends to Display  307 , under the timing control of Computer-based Synchronizer  305 , a sequence of right-eye images and left-eye images corresponding to a computer simulation or game, for example.  
         [0038]    In any case, the Initial Synchronization Sequence  309  is identified by Detector  311  of 3-D Glasses  313 . Upon detection of the Initial Synchronization Sequence  309  the Detector  311  notifies Headgear Synchronization Circuit  315  that the Initial Synchronization Sequence  309  has been received. Headgear Synchronization Circuit  315  then begins cycling Right-eye Shutter  317   a  and Left-eye Shutter  317   b  between their transparent states and their opaque states. The Right-eye Shutter  317   a  and Left-eye Shutter  317   b  are cycled in response to Ongoing Synchronization Signal  319   a  and  319   b  from Headgear Synchronization Circuit  315 . Headgear Synchronization Circuit  315  cycles Right-eye Shutter  317   a  and Left-eye Shutter  317   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  303  shows right-eye and left-eye images on the Display  307 . Headgear Synchronization Circuit  315  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case, suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0039]    Regarding the Initial Synchronization Sequence  309 , this is preferably a predetermined sequence of dark and light images which may readily be detected by Detector  311 . Alternatively, a single image may be utilized rather than a sequence of images. In yet another alternative, the Initial Synchronization Sequence  309  may be one or more images of a predetermined color, or containing predetermined data. In any case, the manner of implementing each of these coding and detection alternatives is well known to those of ordinary skill in the art and shall not be described further.  
         [0040]    Referring now to FIG. 4, a flowchart describing the operation of the embodiment of FIG. 3 will now be described. As seen in this FIG. 3, at Step  1  a user initiates the synchronization process by using an input means (such as a keyboard) to command Computer-based Synchronizer  305  to direct Image Generator  303  to display the Initial Synchronization Sequence  309  on Display  307 . There may preferably be a delay between the input by the user initiating the process and the display of the Initial Synchronization Sequence  309  in order to give the user time to position the 3-D Glasses  313  appropriately (that is, so that the Detector  311  has a line-of sight view of Display  307 ). At Step  2  the Initial Synchronization Sequence  309  is identified by Detector  311  of 3-D Glasses  313 . At Step  3  the Detector  311  notifies Headgear Synchronization Circuit  315  that the Initial Synchronization Sequence  309  has been received. At Step  4  Headgear Synchronization Circuit  315  cycles Right-eye Shutter  317   a  and Left-eye Shutter  317   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  303  shows right-eye and left-eye images on the Display  307 .  
         [0041]    Referring now to FIG. 5, a second embodiment of the instant invention is shown. As seen in this FIG. 5, Computer  501  (which may include input means such as a keyboard, a joystick, and a mouse, all of which are not shown) incorporates Image Generator  503  and Computer-based Synchronizer  505 . Each of Image Generator  503  and Computer-based Synchronizer  505  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a keyboard (not shown) associated with Computer  501  the Computer-based Synchronizer  505  directs Image Generator  503  to display an Initial Synchronization Sequence  509  on Display  507 . This Initial Synchronization Sequence  509  may comprise a sequence of predetermined images. Thereafter, the Image Generator  503  sends to Display  507 , under the timing control of Computer-based Synchronizer  505 , a sequence of right-eye images and left-eye images corresponding to a computer simulation or game, for example.  
         [0042]    In any case, Detector One  511   a  and Detector Two  511   b  of 3-D Glasses  513  are placed adjacent the Display  507 . Upon detection of stimulus such as light of a certain intensity or color each of Detector One  511   a  and Detector Two  511   b  notifies Comparison Circuit  512 . Comparison Circuit  512  uses the input from Detector One  511   a  and Detector Two  511   b  to determine when Initial Synchronization Sequence  509  has been received. When Comparison Circuit  512  determines that the Initial Synchronization Signal  509  has been received it so notifies Headgear Synchronization Circuit  515 . Headgear Synchronization Circuit  515  then begins cycling Right-eye Shutter  517   a  and Left-eye Shutter  517   b  between their transparent states and their opaque states. The Right-eye Shutter  517   a  and Left-eye Shutter  517   b  are cycled in response to Ongoing Synchronization Signal  519   a  and  519   b  from Headgear Synchronization Circuit  515 . Headgear Synchronization Circuit  515  cycles Right-eye Shutter  517   a  and Left-eye Shutter  517   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  503  shows right-eye and left-eye images on the Display  507 . Headgear Synchronization Circuit  515  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case, suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0043]    Regarding the Initial Synchronization Sequence  509 , this is preferably a predetermined sequence of images having predetermined light and dark areas which may readily be detected by Detector One  511   a  and Detector Two  511   b . Each of the light and dark areas may preferably comprise one-half of the Display  507 . Alternatively, a single image may be utilized rather than a sequence of images. In yet another alternative, the Initial Synchronization Sequence  509  may be one or more images of a predetermined color, or containing predetermined data. In any case, the manner of implementing each of these coding and detection alternatives is well known to those of ordinary skill in the art and shall not be described further.  
         [0044]    Referring now to FIG. 6, a flowchart describing the operation of the embodiment of FIG. 5 will now be described. As seen in this FIG. 6, at Step  1  a user initiates the synchronization process by using an input means (such as a keyboard) to command Computer-based Synchronizer  505  to direct Image Generator  503  to display the Initial Synchronization Sequence  509  on Display  507 . There may preferably be a delay between the input by the user initiating the process and the display of the Initial Synchronization Sequence  509  in order to give the user time to position the 3-D Glasses  513  appropriately (that is, so that the Detector One  511   a  and the Detector Two  511   b  are adjacent the Display  507 ). At Step  2  the Initial Synchronization Sequence  509  is identified by Comparison Circuit  512  using input from Detector One  511   a  and Detector Two  511   b . At Step  3  the Comparison Circuit  512  notifies Headgear Synchronization Circuit  515  that the Initial Synchronization Sequence  509  has been received. At Step  4  Headgear Synchronization Circuit  515  cycles Right-eye Shutter  517   a  and Left-eye Shutter  517   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  503  shows right-eye and left-eye images on the Display  507 .  
         [0045]    Referring now to FIG. 7, a third embodiment of the instant invention is shown. This embodiment is similar to the first and second embodiments except that an Initial Synchronization Signal is carried from the Computer  701  to the 3-D Glasses  712  via a hardwired connection that may be broken after the Initial Synchronization Signal is received. In any case, as seen in this FIG. 7, Computer  701  (which may include input means such as a keyboard, a joystick, and a mouse, all of which are not shown) incorporates Image Generator  703  and Computer-based Synchronizer  705 . Each of Image Generator  703  and Computer-based Synchronizer  705  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a keyboard (not shown) associated with Computer  701  the Computer-based Synchronizer  705  directs Image Generator  703  to send Initial Synchronization Signal  709  to Headgear Synchronization Circuit  710  via Connection  708 . Thereafter, the Image Generator  703  sends to Display  707 , under the timing control of Computer-based Synchronizer  705 , a sequence of right-eye images and left-eye images corresponding to a computer simulation or game, for example. The user may break Connection  708  after the Initial Synchronization Signal is sent to Headgear Synchronization Circuit  710 .  
         [0046]    In any case, after the Initial Synchronization Signal  709  has been received Headgear Synchronization Circuit  710  then begins cycling Right-eye Shutter  711   a  and Left-eye Shutter  711   b  between their transparent states and their opaque states. The Right-eye Shutter  711   a  and Left-eye Shutter  711   b  are cycled in response to Ongoing Synchronization Signal  713   a  and  713   b  from Headgear Synchronization Circuit  710 . Headgear Synchronization Circuit  710  cycles Right-eye Shutter  711   a  and Left-eye Shutter  711   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  703  shows right-eye and left-eye images on the Display  707 . Headgear Synchronization Circuit  710  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0047]    Referring now to FIG. 8, a flowchart describing the operation of the embodiment of FIG. 7 will now be described. As seen in this FIG. 8, at Step  1  a user initiates the synchronization process by using an input means (such as a keyboard) to command Computer-based Synchronizer  705  to send the Initial Synchronization Signal  709  to the Headgear Synchronization Circuit  710  via Connection  708 . At Step  2  the Initial Synchronization Signal is received by Headgear Synchronization Circuit  710 . At Step  3  the Connection  708  may be broken by the user if desired at this point forward. At Step  4  Headgear Synchronization Circuit  710  cycles Right-eye Shutter  711   a  and Left-eye Shutter  711   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  703  shows right-eye and left-eye images on the Display  707 .  
         [0048]    Regarding the Connection  708  it is noted that this may be any suitable connection for carrying the Initial Synchronization Signal  709  between the Computer-based Synchronizer  705  and the Headgear Synchronization Circuit  710 . For example, a wire with easily connectable plugs or jacks at one or both ends may be used. In the alternative, there may be a more direct connection between the Computer  701  and the  3 -D Glasses  712 , such as mating electrical connections. In this regard it is noted that Computer-based Synchronizer  705  may send Initial Synchronization Signal  709  to Headgear Synchronization Circuit  710  whenever there is a connection between the two and thus no user input would be required to initiate the synchronization process.  
         [0049]    Referring now to FIG. 9, a fourth embodiment of the instant invention is shown. As seen in this FIG. 9, Video Game Console  901  (which may include input means such as a joystick, which is not shown) incorporates Image Generator  903  and Console-based Synchronizer  905 . Each of Image Generator  903  and Console-based Synchronizer  905  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a joystick (not shown) associated with Video Game Console  901  the Console-based Synchronizer  905  directs Image Generator  903  to display an Initial Synchronization Sequence  909  on Display  907 . This Initial Synchronization Sequence  909  may comprise a sequence of predetermined images. Thereafter, the Image Generator  903  sends to Display  907 , under the timing control of Console-based Synchronizer  905 , a sequence of right-eye images and left-eye images corresponding to a video game, for example.  
         [0050]    In any case, the Initial Synchronization Sequence  909  is identified by Detector  911  of 3-D Glasses  913 . Upon detection of the Initial Synchronization Sequence  909  the Detector  911  notifies Headgear Synchronization Circuit  915  that the Initial Synchronization Sequence  909  has been received. Headgear Synchronization Circuit  915  then begins cycling Right-eye Shutter  917   a  and Left-eye Shutter  917   b  between their transparent states and their opaque states. The Right-eye Shutter  917   a  and Left-eye Shutter  917   b  are cycled in response to Ongoing Synchronization Signal  919   a  and  919   b  from Headgear Synchronization Circuit  915 . Headgear Synchronization Circuit  915  cycles Right-eye Shutter  917   a  and Left-eye Shutter  917   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  903  shows right-eye and left-eye images on the Display  907 . Headgear Synchronization Circuit  915  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case, suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0051]    Regarding the Initial Synchronization Sequence  909 , this is preferably a predetermined sequence of dark and light images which may readily be detected by Detector  911 . Alternatively, a single image may be utilized rather than a sequence of images. In yet another alternative, the Initial Synchronization Sequence  909  may be one or more images of a predetermined color, or containing predetermined data. In any case, the manner of implementing each of these coding and detection alternatives is well known to those of ordinary skill in the art and shall not be described further.  
         [0052]    Referring now to FIG. 10, a flowchart describing the operation of the embodiment of FIG. 9 will now be described. As seen in this FIG. 9, at Step  1  a user initiates the synchronization process by using an input means (such as a joystick) to command Console-based Synchronizer  905  to direct Image Generator  903  to display the Initial Synchronization Sequence  909  on Display  907 . There may preferably be a delay between the input by the user initiating the process and the display of the Initial Synchronization Sequence  909  in order to give the user time to position the 3-D Glasses  913  appropriately (that is, so that the Detector  911  has a line-of sight view of Display  907 ). At Step  2  the Initial Synchronization Sequence  909  is identified by Detector  911  of  3 -D Glasses  913 . At Step  3  the Detector  911  notifies Headgear Synchronization Circuit  915  that the Initial Synchronization Sequence  909  has been received. At Step  4  Headgear Synchronization Circuit  915  cycles Right-eye Shutter  917   a  and Left-eye Shutter  917   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  903  shows right-eye and left-eye images on the Display  907 .  
         [0053]    Referring now to FIG. 11, a fifth embodiment of the instant invention is shown. As seen in this FIG. 11, Video Game Console  1101  (which may include input means such as a joystick, which is not shown) incorporates Image Generator  1103  and Console-based Synchronizer  1105 . Each of Image Generator  1103  and Console-based Synchronizer  1105  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a joystick (not shown) associated with Video Game Console  1101  the Console-based Synchronizer  1105  directs Image Generator  1103  to display an Initial Synchronization Sequence  1109  on Display  1107 . This Initial Synchronization Sequence  1109  may comprise a sequence of predetermined images. Thereafter, the Image Generator  1103  sends to Display  1107 , under the timing control of Console-based Synchronizer  1105 , a sequence of right-eye images and left-eye images corresponding to a video game, for example.  
         [0054]    In any case, Detector One  1111   a  and Detector Two  1111   b  of 3-D Glasses  1113  are placed adjacent the Display  1107 . Upon detection of stimulus such as light of a certain intensity or color each of Detector One  1111   a  and Detector Two  1111   b  notifies Comparison Circuit  1112 . Comparison Circuit  1112  uses the input from Detector One  1111   a  and Detector Two  1111   b  to determine when Initial Synchronization Sequence  1109  has been received. When Comparison Circuit  1112  determines that the Initial Synchronization Signal  1109  has been received it so notifies Headgear Synchronization Circuit  1115 . Headgear Synchronization Circuit  1115  then begins cycling Right-eye Shutter  1117   a  and Left-eye Shutter  1117   b  between their transparent states and their opaque states. The Right-eye Shutter  1117   a  and Left-eye Shutter  1117   b  are cycled in response to Ongoing Synchronization Signal  1119   a  and  1119   b  from Headgear Synchronization Circuit  1115 . Headgear Synchronization Circuit  1115  cycles Right-eye Shutter  1117   a  and Left-eye Shutter  1117   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  1103  shows right-eye and left-eye images on the Display  1107 . Headgear Synchronization Circuit  1115  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case, suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0055]    Regarding the Initial Synchronization Sequence  1109 , this is preferably a predetermined sequence of images having predetermined light and dark areas which may readily be detected by Detector One  1111   a  and Detector Two  1111   b . Each of the light and dark areas may preferably comprise one-half of the Display  1107 . Alternatively, a single image may be utilized rather than a sequence of images. In yet another alternative, the Initial Synchronization Sequence  1109  may be one or more images of a predetermined color, or containing predetermined data. In any case, the manner of implementing each of these coding and detection alternatives is well known to those of ordinary skill in the art and shall not be described further.  
         [0056]    Referring now to FIG. 12, a flowchart describing the operation of the embodiment of FIG. 11 will now be described. As seen in this FIG. 12, at Step  1  a user initiates the synchronization process by using an input means (such as a joystick) to command Console-based Synchronizer  1105  to direct Image Generator  1103  to display the Initial Synchronization Sequence  1109  on Display  1107 . There may preferably be a delay between the input by the user initiating the process and the display of the Initial Synchronization Sequence  1109  in order to give the user time to position the  3 -D Glasses  1113  appropriately (that is, so that the Detector One  1111   a  and the Detector Two  1111   b  are adjacent the Display  1107 ). At Step  2  the Initial Synchronization Sequence  1109  is identified by Comparison Circuit  1112  using input from Detector One  1111   a  and Detector Two  1111   b . At Step  3  the Comparison Circuit  1112  notifies Headgear Synchronization Circuit  1115  that the Initial Synchronization Sequence  1109  has been received. At Step  4  Headgear Synchronization Circuit  1115  cycles Right-eye Shutter  1117   a  and Left-eye Shutter  1117   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  1103  shows right-eye and left-eye images on the Display  1107 .  
         [0057]    Referring now to FIG. 13, a sixth embodiment of the instant invention is shown. This embodiment is similar to the fourth and fifth embodiments except that an Initial Synchronization Signal is carried from the Video Game Console  1301  to the 3-D Glasses  1312  via a hard-wired connection that may be broken after the Initial Synchronization Signal is received. In any case, as seen in this FIG. 13, Video Game Console  1301  (which may include input means such as a joystick, which is not shown) incorporates Image Generator  1303  and Console-based Synchronizer  1305 . Each of Image Generator  1303  and Console-based Synchronizer  1305  may be implemented with hardware, with software, or with a combination of both. When directed by a user through input means such as a joystick (not shown) associated with Video Game Console  1301  the Console-based Synchronizer  1305  directs Image Generator  1303  to send Initial Synchronization Signal  1309  to Headgear Synchronization Circuit  1310  via Connection  1308 . Thereafter, the Image Generator  1303  sends to Display  1307 , under the timing control of Console-based Synchronizer  1305 , a sequence of right-eye images and left-eye images corresponding to a video game, for example. The user may break Connection  1308  after the Initial Synchronization Signal is sent to Headgear Synchronization Circuit  1310 .  
         [0058]    In any case, after the Initial Synchronization Signal  1309  has been received Headgear Synchronization Circuit  1310  then begins cycling Right-eye Shutter  1311   a  and Left-eye Shutter  1311   b  between their transparent states and their opaque states. The Right-eye Shutter  1311   a  and Left-eye Shutter  1311   b  are cycled in response to Ongoing Synchronization Signal  1313   a  and  1313   b  from Headgear Synchronization Circuit  1310 . Headgear Synchronization Circuit  1310  cycles Right-eye Shutter  1311   a  and Left-eye Shutter  1311   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  1303  shows right-eye and left-eye images on the Display  1307 . Headgear Synchronization Circuit  1310  may maintain synchronization using any suitable means, such as a Phase Locked Loop. In any case, suitable synchronization means are well known to those of ordinary skill in the art and shall not be described further.  
         [0059]    Referring now to FIG. 14, a flowchart describing the operation of the embodiment of FIG. 13 will now be described. As seen in this FIG. 14, at Step  1  a user initiates the synchronization process by using an input means (such as a joystick) to command Console-based Synchronizer  1305  to send the Initial Synchronization Signal  1309  to the Headgear Synchronization Circuit  1310  via Connection  1308 . At Step  2  the Initial Synchronization Signal is received by Headgear Synchronization Circuit  1310 . At Step  3  the Connection  1308  may be broken by the user if desired at this point forward. At Step  4  Headgear Synchronization Circuit  1310  cycles Right-eye Shutter  1311   a  and Left-eye Shutter  1311   b  at phases substantially 180 degrees out of phase with one another and at a predetermined frequency which substantially matches the frequency with which the Image Generator  1303  shows right-eye and left-eye images on the Display  1307 .  
         [0060]    Regarding the Connection  1308  it is noted that this may be any suitable connection for carrying the Initial Synchronization Signal  1309  between the Console-based Synchronizer  1305  and the Headgear Synchronization Circuit  1310 . For example, a wire with easily connectable plugs or jacks at one or both ends may be used. In the alternative, there may be a more direct connection between the Video Game Console  1301  and the 3-D Glasses  1312 , such as mating electrical connections. In this regard it is noted that Console-based Synchronizer  1305  may send Initial Synchronization Signal  1309  to Headgear Synchronization Circuit  1310  whenever there is a connection between the two and thus no user input would be required to initiate the synchronization process.  
         [0061]    While a number of embodiments of the instant invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. For example, while the embodiments described refer principally to simulations and games played on computers and video game consoles, the instant invention may of course be applied to other display systems and other content, such as movies, broadcast television, recorded video (i.e., VCR&#39;s, Video Disks, DVD&#39;s, etc), and digital media files, to name a few. Further, while the embodiments described refer principally to 3-D imaging systems, the instant invention may of course be applied to other imaging systems using shutters which must be synchronized with a sequence of images, such as described in U.S. Pat. No. 5,892,505 to Tropper relating to an apparatus and method for displaying on a display screen a first image sequence exclusively to a first viewer and a second image sequence exclusively to a second viewer. Further still, it is noted that embodiments of the instant invention utilizing detector(s) to detect an Initial Synchronization Sequence may employ a moveable shade or shutter over the detector(s) which blocks ambient light from reaching the detector(s) when the detector(s) are not in use. Further still, the headgear of the instant invention may include means for indicating when independent synchronization by the headgear is active. Such indicating means may comprise an LED or LCD, for example. Further still, while embodiments of the instant invention using 1 and 2 detector(s) for detecting the Initial Synchronization Sequence have been described any number of suitable detectors may of course be utilized.