Multiviewer display system for television monitors

A display monitor (12) operates in a time-multiplexed fashion to display a plurality of viewer-selected video channels on a single display screen. A visual apparatus (22) worn by the viewers is synchronized to the operation of the display monitor for enabling each of the viewers to observe the display screen only at times when the viewer-selected video channel is being displayed.

FIELD OF THE INVENTION
 This invention is related to television (TV) monitors and display systems
 and, in particular, to display systems providing simultaneous visual/audio
 presentations to a plurality of viewers.
 BACKGROUND OF THE INVENTION
 A problem is created when different people desire to view different TV
 programs, or to listen to audio in different languages. In a home
 environment this situation typically results in different members of the
 family watching different TVs in different rooms of the home. For a number
 of reasons this common solution to the problem is less than desirable. For
 example, this solution to the problem requires the family to own multiple
 TVs, and possibly multiple reception devices, such as cable converter
 boxes and/or satellite antennas. This problem is compounded if one of the
 TVs is a large screen TV, which may be in demand by all of the family
 members.
 In the field of stereo computer graphics it is known to project different
 images for the left and right eyes. A viewer then uses so-called shutter
 glasses to view the image in stereo. The shutter glass system works by
 closing the shutter for one eye for a brief period during which the other
 eye views what is displayed on the screen. This process is alternated for
 the left eye and the right eye. The images on the screen are adapted for
 each eye, based on the displacement between the viewer's eyes. So when the
 shutter for the left eye is open, it displays the image for the left eye
 and vice-versa. The persistence of human vision ensures that the images
 are "seen" simultaneously. The use of such a system enables a viewer to
 view a displayed image in a stereoscopic sense, and thus perceive depth.
 In greater detail, in such traditional stereo graphics displays a receiver
 on the shutter glasses, such as an infrared (IR) receiver, receives a
 synchronization signal from the stereo monitor. The synchronization signal
 causes liquid crystal (LC) panels or shutters in the glasses (one for each
 eye) to switch from being opaque to transparent and vice versa. When
 opaque, the viewer cannot see through the shutter. The shutter for the
 left and right eye switch in an alternate fashion and, at any given time,
 only one eye can see the displayed image. However, the persistence of
 human vision results in both eyes seeing their corresponding images
 simultaneously.
 While the LC shutters are being controlled in this fashion, the display
 monitor is displaying images alternately for the left eye and right eye.
 The image for the left eye differs from the image for the right eye. This
 difference is what gives the perception of depth. In a computer generated
 image, the image for the left eye is created by treating the center of the
 camera to coincide with the center of the left eye and vice-versa. As a
 result, the two images differ in camera position.
 Some stereo and virtual reality systems use small displays (e.g., LCDs)
 provided within head sets worn by a user. However, the use of such a
 system presents at least two problems. The first is the current low
 resolution of such displays, resulting in poor image quality. The second,
 and more important problem, is that the use of the head set isolates the
 viewer from his or her surroundings, making it difficult for the viewer to
 interact with objects and persons in the viewer's environment.
 At present, there is no system known to the inventor that allows viewers to
 simultaneously watch different programs using the same TV monitor.
 OBJECTS OF THE INVENTION
 It is a first object of this invention to provide a solution to the
 foregoing problems that enables multiple viewers in a room to
 unobtrusively and simultaneously view different TV programs.
 It is a further object of this invention to provide a display monitor that
 operates in a time-multiplexed fashion to display a plurality of
 viewer-selected video channels on a single display screen, and to also
 provide visual apparatus worn by the viewers, the video apparatus being
 synchronized to the operation of the display monitor for enabling each of
 the viewers to observe the display screen only at times when the
 viewer-selected video channel is being displayed.
 SUMMARY OF THE INVENTION
 The foregoing and other problems are overcome and the objects of the
 invention are realized by methods and apparatus in accordance with
 embodiments of this invention.
 In a method of this invention steps are disclosed for simultaneously
 viewing a plurality of video channels, on one display screen, with a
 plurality of viewers. The steps of the method include (a) providing each
 of the plurality of viewers with visual apparatus that operates in two
 modes, wherein in a first mode the viewer is enabled to view an image on
 the display screen through the visual apparatus, while in the second mode
 the viewer is disabled by the visual apparatus from viewing an image on
 the display screen. A second step (b) operates a display monitor that
 includes the display screen so as to time multiplex the display of a
 plurality of video channels selected by the plurality of viewers. A third
 step (c) synchronizes the operation of each of the plurality of visual
 apparatus with the display screen such that each viewer is enabled to view
 the image on the display screen only during a time when a viewer-selected
 video channel is being displayed on the display screen.
 The visual apparatus includes at least one electrically actuated liquid
 crystal shutter that is transparent in the first mode and opaque in the
 second mode, and wherein the step of synchronizing includes a step of
 transmitting information to the visual apparatus, preferably over a
 wireless link, for indicating a time when the at least one liquid crystal
 shutter is to switch from being transparent to being opaque, and from
 being opaque to being transparent.
 The method further includes steps of: (d) receiving, at each of the visual
 apparatus, an audio channel associated with the viewer-selected video
 channel; and (e) converting the received audio channel into an audio
 signal for the viewer.
 At least one of the video channels may provide access to a data
 communications network such as the internet.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to FIG. 1, and in accordance with the teaching of this invention,
 a TV monitor 12 receives a signal from a broadcaster 14 through a
 conventional rooftop or satellite antenna, or though a coaxial cable or a
 fiber optic cable. Signals may also be received from a computer interface,
 a VCR, a video game interface, an internet television interface, or any
 device capable of generating video and/or audio for display or
 reproduction on a television monitor. These plurality of program sources,
 and individual channels within a given program source, may be considered,
 for the purposes of this invention, to represent a plurality of video
 channels. Preferably the TV monitor 12 is a digital TV monitor, such as
 one compatible with a specification entitled ATSC Digital Television
 Standard, Doc. A/53, Sep. 16, 1995, by James C. McKinney and Robert
 Hopkins, that is modified in accordance with the teachings of this
 invention.
 Each viewer, for example three viewers A, B and C, is provided with a video
 apparatus embodied as a pair of shutter glasses 22 (see FIGS. 5 and 7,
 described below). Each pair of shutter glasses 22 (designated 22A, 22B and
 22C) includes a pair of electrically or mechanically actuated shutters
 (24A, 24B) which are positioned in front of the left and right eyes,
 respectively. The shutters 24A and 24B are preferably LC shutters that can
 be rapidly switched between an opaque and a transparent state. In this
 invention, as opposed to the conventional shutter glasses used for viewing
 three dimensional stereoscopic displays, the two shutters 24A and 24B are
 operated simultaneously to either both pass light to the viewer's eyes or
 both block
 light from reaching the viewer's eyes. The shutter glasses 22 also include
 one or more earphones or speakers 25, and a receiver, such as an IR
 receiver 23, for receiving control, synchronization, and possibly audio
 signals from a corresponding IR transmitter 12A located at the TV monitor
 12. In other embodiments of this invention a wired connection could be
 made between the shutter glasses 22 and the monitor 12, or a radio
 frequency connection could be made. The particular type of connection made
 between the TV monitor 12 and the shutter glasses 22 is not particularly
 important, so long as the selected communication medium can support the
 required communication protocol, while being unobtrusive to the user. As
 such, an IR wireless connection is preferred.
 Each viewer also has an associated, separately identifiable remote control
 (RC) 28 for at least selecting a video channel to be viewed. Other
 functions, such as adjusting or muting the audio volume, etc., can
 typically also be performed using the remote control 28.
 The TV monitor 12 has the capability to vary its refresh rate to
 simultaneously provide different programs to variable numbers of viewers.
 For example, instead of refreshing one channel at 60 Hz, the TV monitor 12
 refreshes the channel for each of the viewers at 60 Hz. For the case where
 there are three viewers A, B, C, as in FIG. 1, who have different viewing
 preferences, the TV monitor 12 refreshes one frame for viewer A, followed
 by one frame for viewer B, and then one frame for viewer C, before
 returning to the next frame for A and so on. This order of viewer
 refreshing is not mandatory, as shown in FIG. 6C, as the viewer's frames
 could be refreshed in some other order.
 In the example of FIG. 1 the TV monitor 12 refreshes at a compound rate of
 60*3=180 Hz. Conventional display screen phosphor persistence ranges from
 10 to 60 microseconds for a typical computer screen. However, low
 persistence phosphors with persistence times in the range of 70 to 150
 nanoseconds are available and are preferred, as the TV monitor screen can
 be refreshed at significantly higher rates than the current maximum of
 105-135 Hz, even with the 60 microsecond persistence phosphors. As is well
 known, the persistence of the human visual system is at least 1/24 of a
 second, as motion pictures are shown at 24 frames/sec.
 The shutter glasses 22 for each viewer are synchronized with the operation
 of the TV monitor 12, as shown in FIG. 2. The TV monitor 12 transmits
 synchronization signals to synchronize the operation of the left and right
 shutters 24A and 24B for each viewer. The shutter glasses 22 receive the
 synchronization signals and regulate the opening and closing of the
 shutters 24A and 24B in accordance therewith. As can be seen, viewer A's
 shutter glasses 22 (both eyes) are open when the TV monitor 12 is
 displaying the viewer A's channel (Channel A), and are closed while the TV
 monitor 12 is displaying the Channels B and C for the other two viewers B
 and C, respectively. The operation is the same when displaying Channels B
 and C, such that each viewer is enabled to view only his or her selected
 channel. In that the channels are displayed at a rate that exceeds the
 persistence period of human vision, the viewer sees the associated channel
 with out flicker, and is not aware of the images displayed for the other
 viewers.
 The audio portion is customized for each viewer by broadcasting a compound
 signal that is decoded in the shutter glasses 22 such that each viewer's
 shutter glasses 22 receives the audio for the correct channel. Each viewer
 may receive high fidelity stereo sound. The audio information may be
 broadcast using either a wired or wireless connection, with the wireless
 connection being preferred.
 It should be noted that the shutter glasses 22 in accordance with an aspect
 of this invention do not have the physiological drawbacks, such as eye
 strain, that is associated with conventional stereo glasses. Eye strain
 occurs while viewing a stereoscopic display because content providers
 typically employ a significant amount of depth disparity to enhance the
 viewer's perception of depth. Also, the viewer's visual system is strained
 to coordinate the two different images being seen (first left, then right,
 then left, etc.) In the instant invention both eyes view the same image,
 and there is no depth disparity. As such, eye strain is reduced or
 eliminated.
 The IR transmitter 12A could be isolated from the TV monitor 12 (such as
 being ceiling mounted) and, in such a system, the TV monitor 12 includes
 an IR receiver, like that of the shutter glasses 22, in order to switch
 between selected channels.
 One conventional type of stereoscopic shutter glasses are available from
 StereoGraphics.TM. Corporation, and are known as SimulEyes.TM. VR. In this
 product a cable connects the glasses to the video output of the computer,
 and electronics in the glasses is responsive to the display
 synchronization signals to alternately activate left and right eye LC
 shutters.
 The shutter glasses 22 of this invention can be similar in some respects to
 such conventional stereoscopic shutter glasses, but are otherwise modified
 to operate both LC shutters simultaneously, to adjust the timing to
 variable numbers of viewers, and to provide selective audio decoding, as
 described below.
 Since there may be more than one channel being displayed each pair of
 glasses 22 is required to know when it should activate the LC shutters 24A
 and 24B. As such, the TV monitor 12 informs each pair of shutter glasses
 22 (via the IR transmitter 12A and IR receiver 23) of the length of time
 for which it should control the LC shutters 24A and 24B to be transparent
 and opaque.
 In a first embodiment of this invention a signal is sent to each pair of
 shutter glasses 22 each time the shutter glasses are required to switch
 states, thereby maintaining continuous, active synchronization of the
 operation of each pair of shutter glasses 22 to the operation of the TV
 monitor 12. In a second embodiment the shutter glasses 22 are only
 initially or periodically synchronized to the operation of the monitor 12,
 and thereafter each pair of shutter glasses 22 maintains synchronization
 using an internal synchronizing clock. Only when a change in the viewing
 situation occurs, such as when a new viewer is added, is another active
 synchronization signal sent from the monitor 12 to the pairs of shutter
 glasses 22, as shown in the logic flow diagram of FIG. 4. The first
 embodiment simplifies the design and operation of the shutter glasses 22,
 while the second embodiment simplifies the design and operation of the
 monitor 12.
 FIG. 6A illustrates the timing for the first embodiment described above.
 Assume the signal is transmitted for viewer A, and that the signal is
 modulated to indicate the shutter open and closed times. The signal for
 viewer A is distinguished from the signals transmitted for viewer B
 (assuming two viewers for this example) by, for example, either amplitude
 modulation or frequency modulation.
 FIG. 6B illustrates an embodiment of a monitor signal command packet that
 is transmitted by the monitor 12 in accordance with the second embodiment.
 The command packet includes, by example, the current number of viewers,
 the viewing order (e.g., viewers A, B, C, or viewers A, C, B), and
 transmitted frequencies, or markers in a composite audio data stream, of
 associated audio channels. The command packet need be sent only when the
 viewing situation changes (e.g., a viewer is added or dropped).
 FIG. 6C illustrates a further aspect of this second embodiment, and assumes
 the viewing order of viewer A, C, B. In this embodiment a synchronizing
 signal 19 can be transmitted by the monitor 12 at the beginning of every
 viewing cycle. For example, based on the number of viewers and viewing
 order received in the command packet of FIG. 6B, a given pair of shutter
 glasses 22 can determine the duration of the viewer's viewing slot during
 one viewing cycle, and the beginning and end of the viewer's slot relative
 to the other viewing slots. By example, assume that the viewing cycle has
 a duration of x milliseconds, and that from the command packet of FIG. 6B
 the shutter glasses 22 determine that there are three viewers ordered as
 A, C, B. The viewing period for one pair of shutter glasses 22 is thus x/3
 milliseconds, the viewing period for viewer A starts coincident with the
 synchronizing signal 19 and ends x/3 milliseconds later, the viewing
 period for viewer C starts x/3 milliseconds after the synchronizing signal
 19, and ends 2x/3 milliseconds later, and the viewing period for viewer B
 starts 2x/3 milliseconds after the synchronizing signal 19, and ends 3x/3
 milliseconds later, or coincident with the next synchronizing signal 19.
 Referring to FIGS. 5 and 7 there is illustrated an elevational front view
 of a representative pair of shutter glasses 22, and a simplified diagram
 of the electronics 30 of a pair of shutter glasses 22, respectively. The
 IR receiver 23 is comprised of an IR detector 32 and an amplifier,
 receiver, demodulator 34. The output of the receiver 34 is applied to a
 controller 36 wherein time slot decoding, LC shutter timing, and audio
 functions are performed. Each pair of shutter glasses 22 preferably
 includes an audio decoding apparatus for use with a digital TV monitor 12
 that digitally broadcasts the audio for all viewed channels as a digital
 stream. A given pair of shutter glasses 22 receives and demodulates the
 audio data stream, selects the audio data associated with the channel
 being viewed, and converts the digital data to an analog signal in a D/A
 controller 38. The audio signal is then applied to one or more earphones
 or speakers 25 so that each viewer is individually supplied with the audio
 portion of the channel being viewed.
 In another embodiment the audio stream for each channel is decoded in the
 monitor 12 and is then either amplitude or frequency modulated and
 transmitted into the room on a transmitted audio frequency channel (e.g.,
 for three viewers three different audio frequency channels are used). The
 shutter glasses 22 tune to and select their assigned frequency and receive
 the audio for their channel. The shutter glasses 22 are informed of the
 transmitted frequency of the associated audio channel by the command
 packet shown in FIG. 6B. The IR link can be modulated so as to convey the
 audio portion, or a separate transmitter/receiver link (e.g., a low power
 FM RF link) can be used.
 As was stated above, the TV monitor 12 is preferably a digital television
 monitor that is modified so as to operate with the shutter glasses 22.
 Further modifications relate to the time-multiplexed channel display and
 to the interaction with the remote controls 28.
 Digital TV monitors currently have the ability to receive and decode many
 channels simultaneously. These channels may be received via cable,
 satellite or terrestrial broadcasts, from the internet, or from a VCR.
 They may be analog or digital.
 In accordance with this invention, and referring to FIG. 8, the monitor 12
 has an input for receiving digital signals from one or more programming
 sources and a channel decoder 40 controlled by a monitor controller 42.
 The monitor controller 42 receives inputs from the remote controls 28A-28C
 via an RC interface 44. The signal transmitted from each RC controller 28
 can be separately identified, such as by transmitting a unique
 identification tag, so that a given viewer's channel selection, volume
 control, etc. can be separately identified. Based on the selected channel
 from each remote control 28, that channel's video information is stored in
 a corresponding channel full frame buffer (e.g., channel frame buffers
 A-C) 46, 48, 50. For HDTV applications each frame buffer 46, 48, 50 may
 have a number of storage locations to store RGB or YUV data for, by
 example, 1080.times.1920 display screen pixels or 720.times.1280 display
 screen pixels. A channel output multiplexer 52 is controlled by the
 monitor controller 42 so as to timemultiplex the video information onto a
 display screen 54. Digital audio is processed by the controller 42 and
 output to the shutter glasses 22 via the IR transmitter 12A, along with
 command packet and/or synchronization information (see FIGS. 6A-6C). Using
 this technique, and by example, viewer A may be viewing a cable news
 channel, viewer B may be viewing a motion picture received from a cable,
 satellite, or VCR, and viewer C may be browsing the internet using an
 internet television channel and appropriate interface.
 It should be realized that two or more viewers may select the same program
 source, and that each viewer is not required to view a different program.
 In this case it is preferred that those viewers watching the same program
 be placed in the same time slot so that their respective shutter glasses
 22 open and close their shutters 24A and 24B simultaneously. In an
 alternative embodiment each viewer is assigned a separate time slot, and
 the commonly watched channel is simply displayed two or more times during
 one viewing cycle.
 In general, the timing of the occurrence of shutter open and closed times
 within the viewing cycle can be varied by the receipt of the
 synchronization signal to accommodate at least one of a change in a total
 number of viewers, or two or more viewers selecting the same video
 channel.
 It should be further realized that a given viewer may select a video
 channel x, and an audio channel y associated with another video channel,
 assuming that the remote control 28 or some other input device is suitably
 configured. This mode of operation is useful if, for example, a viewer
 wishes to listen to a news or sports broadcast while viewing a movie, or
 wishes to listen to the dialog of a video presentation in another language
 (assuming that the audio portion of channel y is synchronized with the
 video portion of channel x).
 Still referring to FIG. 8, in an alternative embodiment a single channel
 frame buffer may be reused for different channels. However, the required
 synchronization and decoding may make this a less desirable approach to
 the use of separate frame buffers 46-48.
 When a given one of the remote controls 28A-28C issues a command the TV
 monitor 12 receives it via the RC interface 44 and takes the necessary
 action, as shown in Block F of FIG. 3. Any changes become visible at the
 start of next time slot for the associated viewer.
 When the TV monitor 12 is first turned on it may initialize to a single
 viewer, non-multiplexed mode, wherein a default channel or a last selected
 channel is displayed. The monitor may stay in the single viewer mode so
 long as it receives inputs from only one remote control 28. However, as
 soon as an input is received from a second remote control 28, the monitor
 12 switches to a two viewer, time-multiplexed mode, requiring the use of
 the shutter glasses 22 to view two selected channels. The receipt of an
 input from a third remote control 28 places the monitor into a three
 viewer time-multiplexed mode, etc. Each remote control 28 can be provided
 with a button that functions as an on-off button, or simply as an off
 button, so that a viewer can signal that he or she has stopped viewing the
 monitor 12. By example, and if operating in the two viewer
 time-multiplexed mode, the receipt of the off signal from one of the
 remote controls 28 causes the monitor 12 to revert to the single viewer,
 non-multiplexed mode, and to display only the channel selected by the
 still active remote control 28.
 It is also within the scope of this invention to provide an activity signal
 from a pair of shutter glasses 22 to indicate to the monitor 12 that the
 shutter glasses are operational. For example, switching on a power switch
 on the shutter glasses 22 may cause a transmitter mounted in the shutter
 glasses 22 to transmit a signal (through a wired or wireless link) to a
 suitable receiver at the monitor. A number of different embodiments of
 activity signal generating devices can be provided. As one further
 example, a small microswitch or a proximity sensor can be positioned in
 the shutter glasses 22 at a location where the microswitch or sensor is
 activated only when the shutter glasses are worn by a viewer. In this case
 the monitor 12 can be notified of those times when the viewer is actually
 wearing the shutter glasses 22, and is assumed to be watching his or her
 selected video channel.
 Referring to FIG. 3, it can be seen that at Block A the monitor 12
 determines if only one channel is being viewed. If yes, control passes to
 Block B to operate as a conventional television display. If no at Block A,
 control passes to Block C to determine the number of distinct channels
 being viewed, and then to Block D to inform the viewers, such as by the
 command packet of FIG. 6B, as to the number of viewers and channel order.
 At Block E the monitor 12 cycles through and displays all of the currently
 selected channels in one viewing cycle (see FIG. 6C), and then determines
 at Block F if a channel change has been commanded from one of the remote
 controls 28. If yes, control passes to Block A, else control passes to
 Block E to display the selected channels during the next viewing cycle.
 During this time each pair of active shutter glasses 22 operates in
 accordance with the logic flow diagram of FIG. 4. At Block A the shutter
 glass controller 36 receives and decodes a command packet as described
 above. At Block B the controller 36 simultaneously opens and then closes
 the LC shutters during the assigned viewing slot, and at Block C makes a
 determination if any change has been indicated as occurring in the viewing
 or listening configuration. If no, control passes to Block B to continue
 operating the LC shutters at the appropriate times, otherwise control
 passes to Block A to determine the new viewing and timing parameters.
 Although described above in the context of shutter glasses that employ
 separate shutters 24A and 24B for the left and right eyes, in other
 embodiments of this invention a single, larger shutter could be employed
 for blocking light from reaching both eyes. Also, while described above
 primarily in the context of a three-viewer system, more or less that three
 viewers can be served, with the maximum number being a function of
 available display screen phosphor persistence times, and the constraints
 imposed by human visual persistence.
 Thus, while the invention has been particularly shown and described with
 respect to preferred embodiments thereof, it will be understood by those
 skilled in the art that changes in form and details may be made therein
 without departing from the scope and spirit of the invention.