Abstract:
An application for transmission of a three-dimensional eyewear synchronization signal to synchronize the operation of shutters of three-dimensional eyewear uses an industry standard wireless transmission technique. To compensate for inherent latencies of such transmission techniques, the latencies are measured and monitored to determine expected latencies and the shutter synchronization signal is skewed by the latency. In some embodiments, the synchronization signal is further adjusted by a user skew control.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to U.S. patent application titled “PIXEL SYSTEM, METHOD AND APPARATUS FOR SYNCHRONIZING THREE-DIMENSIONAL EYEWEAR,” filed Feb. 1, 2010, attorney docket 10 — 0001. This application is also related to U.S. patent application titled “FRAME SYSTEM, METHOD AND APPARATUS FOR SYNCHRONIZING THREE-DIMENSIONAL EYEWEAR,” filed Feb. 1, 2010, attorney docket 10 — 0002. This application is also related to U.S. patent application titled “PIXEL BASED THREE-DIMENSIONAL ENCODING METHOD,” filed Feb. 1, 2010, attorney docket 10 — 0003. This application is also related to U.S. patent application titled “FRAME BASED THREE-DIMENSIONAL ENCODING METHOD,” filed Feb. 1, 2010, attorney docket 10 — 0004. 
     
    
     FIELD 
       [0002]    This invention relates to the field of display devices worn over an individual&#39;s eyes and more particularly to a system for synchronizing the display devices with content presented on a display screen. 
       BACKGROUND 
       [0003]    There are several ways to present a three-dimensional image to a viewer of a television. The common aspect of the existing methods is to present an image or frame from two perspectives, a left-eye perspective of the content to the left eye and present an image or frame from a right-eye perspective to the right eye. This creates the proper parallax so that the viewer sees both perspectives and interprets what they are seeing as three-dimensional. 
         [0004]    Early three-dimensional content was captured using two separate cameras aimed at the subject but slightly separate from each other providing two different perspectives. This simulates what the left eye and right eye see. The cameras simultaneously exposed two films. Using three-dimensional eyewear, the viewer looks through one film with the left eye and the other film with the right eye, thereby seeing what looks like a three-dimensional image. 
         [0005]    Progressing to motion pictures, three-dimensional movies were produced in a similar way with two cameras, but the resulting images were color encoded into the final film. To watch the film in three-dimension, eyewear with colored filters in either eye separate the appropriate images by canceling out the filter color. This process is capable of presenting a three-dimensional movie simultaneously to a large audience, but has marginal quality and, because several colors are filtered from the content, results in poor color quality, similar to a black and white movie. 
         [0006]    More recently, personal eyewear have been made that have two separate miniature displays, one for each eye. In such, left content is presented on the display viewed by the left eye and right content is presented on the display viewed by the right eye. Such systems work well, but require a complete display system for each viewer. 
         [0007]    Similar to this, Eclipse methods uses a common display, such as a television, along with personal eyewear that have fast-response shutters over each eye. In such, the left eye shutter is open allowing light to pass, the right eye shutter is closed blocking light and the television displays left-eye content, therefore permitting the light (image) from the television to reach the left eye. This is alternated with closing of the left eye shutter, opening of the right eye shutter and displaying right-eye content the television. By alternating faster than the typical human response time, the display appears continuous and flicker-free. 
         [0008]    One problem with the latter two methods is that the three-dimensional content must be encoded on, for example, a disk and decoded by a player that switches between left/right eye content in synchronization with the left-eye and right-eye shutter. With such, one cannot connect an industry standard player (e.g. BlueRay or DVD) to an industry standard television (e.g., Plasma or LCD television) and watch three-dimensional content with a set of three-dimensional eyewear. Another problem is in synchronizing the eyewear with the images displayed on the television. Currently, the three-dimensional eyewear needs to be connected to the television by a low-latency connection, usually a wired connection to assure the proper eyewear shutter is open when the corresponding image is displayed (the image that relates to the eye associated with the open shutter). Although wireless transmission techniques such as WiFi and Bluetooth are well-known, low-cost and readily available, latency is of concern for transmitting a synchronization signal. For example, if at t 0 , the television displays a left-eye frame and at the same time transmits a Bluetooth packet to eyewear, the eyewear doesn&#39;t know the packet has arrived until t 0 +l, where l is the latency of the transmission. The latency, in an ideal transmission, is equal to the packet size divided by the transmission speed. For high-speed transmission such as 54 Mbs 802.11, the latency is normally rather low, but the latency is often increased due to other wireless devices utilizing the same bandwidth, transmission errors, noise and interference (e.g. interference from a microwave oven, etc). Therefore, the latency ranges from microseconds to many milliseconds. In such a transmission system, when synchronization is skewed due to unpredictable latency, the wrong eye shutter is open for too long, allowing each eye to partially see content/frames designated for the other eye; causing blurring or other artifacts that detract from the three-dimensional viewing experience. 
         [0009]    What is needed is a three-dimensional presentation system that utilizes existing packet wireless transmission techniques. 
       SUMMARY 
       [0010]    In order to synchronize the operation of shutters of three-dimensional eyewear, an industry standard wireless transmission technique is utilized. To compensate for inherent latencies of such techniques, the latencies are measured and monitored to determine expected latencies and the shutter synchronization signal is skewed by the measured latency. In some embodiments, the synchronization signal is further adjusted by a user skew control. 
         [0011]    The eyewear includes shutters over each eye that open and close fast enough to keep up with the frame rate of the television. A wireless signal is periodically sent from the television or other base-located device to the eyewear. The eyewear receives the wireless signal and determines a latency between the start of the transmission and the actual start and/or end of reception and subtracts the latency from each successive reception of the wireless signal to operate the shutters in synchronization with the television/base-located device. Examples of the wireless transmission technique include, but are not limited to, WiFi (802.11x) and Bluetooth. 
         [0012]    A content delivery mechanism (e.g. Internet, cable, fiber-optic, DVD, BlueRay) delivers the content to a television. A circuit associated with the television or external to the television determines when either a left-eye frame or a right-eye frame is being displayed and transmits a minimal amount of information to the eyewear by a wireless transmission (e.g. WiFi or Bluetooth). The wireless packet is received by the three-dimensional eyewear where it is used to properly shutter the first eye and the second eye. A latency value is subtracted from (or added to) the time of reception, resulting in a synchronization point (e.g., a point in time when the left-eye content frame is displayed and left eye shutter should be open). After reception of a sequence of packets, the eyewear determines the expected timing of multiple synchronization points, thereby generating an internal synchronization signal that is closely synchronized with the changing of frames displayed on the television, left content frame to right content frame and right content frame to left content frame. In some systems, a phased-locked loop is used to continue operation of the shutters during periods when the latency is significantly longer than expected; the transmission of the synchronization signal is blocked; or otherwise the transmission of the synchronization signal interrupted. In some systems, the skew is adjustable up or down to provide a fine adjustment of the synchronization should the latency calculation be less than optimal. 
         [0013]    In one embodiment, a three-dimensional eyewear synchronization system is disclosed. The three-dimensional eyewear synchronization system has a transmitter that sends a synchronization packet indicating synchronization timing between left-eye content and right-eye content being displayed. The three-dimensional eyewear has a receiver and a shutter system for alternating image viewing to each eye of a wearer. The three-dimensional eyewear receives the synchronization packet, determines the transmission latency and uses a time of receipt of the synchronization packet and the latency to generate an eyewear internal synchronization timing that approximates the synchronization timing. The three-dimensional eyewear controls the shutter system responsive to the eyewear internal synchronization timing. 
         [0014]    In another embodiment, a method of synchronizing three-dimensional eyewear to a display of content is disclosed including, at a synchronization point, sending a synchronization packet to the three-dimensional eyewear then determining a latency of the sending and generating an internal synchronization timing in the eyewear by combining a time of reception of the synchronization packet with the latency to control eye shutters of the three-dimensional eyewear in synchronization with the internal synchronization timing. 
         [0015]    In another embodiment, a three-dimensional eyewear synchronization system is disclosed including a television that has a display and the display presenting left-eye frames and right-eye frames. A device associated with the television is for transmitting a synchronization packet is synchronized to which of the left-eye frame and the right-eye frame is being displayed on the display. Another device associated with three-dimensional eyewear is for receiving the synchronization packet. There is another device for determining a latency of the transmitting of the synchronization packet and another device for synchronizing shutters of the three-dimensional eyewear using a time of reception of the synchronization packet and the latency to approximate the timing of the display of the left-eye frames and the right-eye frames. 
         [0016]    In another embodiment, a three-dimensional eyewear synchronization system is disclosed including a television, the television having a display, the display presenting left-eye frames and right-eye frames and a synchronization signal representing a change between displaying of the left-eye frame and displaying of the right-eye frame on the display. The television includes a device for determining a latency of a transmission of a synchronization packet and a device for transmitting a synchronization packet synchronized to the synchronization signal but retarded in time by the latency (e.g. sent before the synchronization signal). The three-dimensional eyewear have a device for receiving the synchronization packet and have a device for synchronizing shutters to the reception of the synchronization packet, thereby synchronizing approximately with the timing of the display of the left-eye frames and the right-eye frames. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
           [0018]      FIG. 1  illustrates a plan view of a television and three-dimensional eyewear of the prior art. 
           [0019]      FIG. 2  illustrates a plan view of a television and three-dimensional eyewear. 
           [0020]      FIG. 3  illustrates a schematic diagram of a typical receiver circuit of the three-dimensional eyewear. 
           [0021]      FIG. 4  illustrates a schematic diagram of a typical receiver circuit of the three-dimensional eyewear with adjustable skew. 
           [0022]      FIG. 5  illustrates a synchronization timing chart. 
           [0023]      FIG. 6  illustrates a block diagram of a typical television system with wireless synchronization transmission. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures. Throughout the description, the term transmitter and receiver are either independent transmitters or receivers and/or are the transmitter section/receiver section of a transceiver. 
         [0025]    Referring to  FIG. 1 , a plan view of a television  1  and three-dimensional eyewear  10  of the prior art is described. In prior technology, three-dimensional eyewear  10  functioned with content delivery hardware, such a personal computer or specially equipped television  1 . The personal computer or television  1  displays three-dimensional content on a display  2  and controls the eyewear  10  through a cable  18  that provided control of each eye shutter  14 / 16 , synchronizing the eye shutters  14 / 16  to the content being displayed on the display  2 . The eyewear often includes frames with ear rests  12 . In such systems, content contains left-eye and right-eye encoded frames. Specialized hardware and/or software in the personal computer or television  1  displays the content and synchronizes operation of the left/right shutter  14 / 16  with the display of the content using synchronization signals sent over the cable  18 . 
         [0026]    The cable interface  18  was needed to assure proper timing of the left shutter  14  and right shutter  16  when left frames and right frames are displayed on the display  2 . The cables of the prior art create a comfort, distance and safety issue and are not desired. 
         [0027]    Referring to  FIG. 2 , a plan view of a display device (e.g. television)  5  and three-dimensional eyewear  50 A is described. In this, a transmitter device has an antenna  20  integrated in the television  5 . As will be described, the transmitter periodically transmits a synchronization packet  57  to the three-dimensional eye wear  50 A over a wireless transmission channel, for example, using WiFi or Bluetooth. In one example, the synchronization packet  57  is transmitted each time a left-eye content frame is displayed on the display  7 . The synchronization packet  57  is received by an antenna  58  and decoded within the eyewear  50 A or by an attached circuit to the eyewear  50 A (not shown), to control the eyewear shutters  54 / 56  as will be described. Note, in some embodiments, the eyewear  50 A includes ear rests  52  for support. 
         [0028]    Referring to  FIG. 3 , a schematic diagram of a typical receiver circuit  80  of the three-dimensional eyewear  50 A is described. In such, the radio frequency signal (packet)  57  is received on the antenna  58  and detected/demodulated by a transceiver  53 . The transceiver  53  is any known transceiver such as a Bluetooth transceiver or WiFi transceiver. In most packet-based transmission techniques, the entire packet is received and error checked/corrected, then an acknowledgement is transmitted back to the sender (e.g. television  5 ). The transceiver  53  emits a synchronization signal  70  when it receives a timing packet  57 . The synchronization signal  70  is connected to a timing circuit  55 . It is anticipated that in some embodiments, the same transceiver  53  also receives other packets for use within the eyewear  50 A for other purposes such as audio packets, etc. 
         [0029]    The transceiver  53  determines or receives a latency time, l, and relates the latency time, l, to the timing circuit  55  by a latency interface  72  which is any interface as known in the industry such as a voltage, current, digital value (e.g. I 2 C), etc. In some embodiments, the latency time, l, is determined by the transceiver  53  based on the packet  57  size and the current transmission rate. The transceiver knows the transmission rate, which often varies up and down based upon collisions, interference, competing wireless networks, etc. In other embodiments, the latency, l, is determined at the television  5  (or other base-device) by measuring the time from start of transmission of the packet  57  until start or end of reception of the acknowledgement, then allocating part or all of the time to the latency l. For example, if the transmission packet length is 128 bits and the acknowledgement packet length is 64 bits, and the time measured is 12 microseconds, then ⅔ of the time or 8 microseconds is allocated to the latency l. In such, the latency value is then transmitted as part of the next packet  57 , received by the transceiver  53  and provided to the timing circuit  55  over the latency interface  72  for determining synchronization of the shutters  54 / 56 . 
         [0030]    The timing circuit locks onto the synchronization signal  70  and adds or subtracts the latency value to generate a left-eye (Q) control signal and a right-eye (−Q) that are coupled to the left-eye shutter  54  and right-eye shutter  56 , respectively, by shutter drivers  60 / 59 . In the preferred embodiment, the timing circuit  55  includes a phased-locked-loop that provides the left-eye and right-eye control signals during a loss of the synchronization signal  70 , for example when interference temporarily disables transmission of the packets  57 . In some embodiments, the phase-locked-loop also performs a filter function, ignoring spurious extreme latency values that occur, for instance, when the wireless interface is used to transfer data, etc. 
         [0031]    Referring to  FIG. 4 , a schematic diagram of a typical receiver circuit  81  of the three-dimensional eyewear  50 A with adjustable skew is described. In such, the radio frequency signal (packet)  57  is received on the antenna  58  and detected/demodulated by a transceiver  53 . The transceiver  53  is any known transceiver such as a Bluetooth transceiver, WiFi transceiver or infrared transceiver. In most packet-based transmission techniques, the entire packet is received and error checked/corrected, then an acknowledgement is transmitted back to the sender (e.g. television  5 ). The transceiver  53  emits a synchronization signal  70  when it receives a timing packet  57 . The synchronization signal  70  is connected to a timing circuit  55 . It is anticipated that in some embodiments, the same transceiver  53  also receives other packets for use within the eyewear  50 A for other purposes such as audio packets, etc. 
         [0032]    The transceiver  53  determines or receives a latency time, l, and relates the latency time, l, to the timing circuit  55  by a latency interface  72  which is any interface as known in the industry such as a voltage, current, digital value (e.g. I 2 C), etc. In some embodiments, the latency time, l, is determined by the transceiver  53  based on the packet  57  size and the current transmission rate. The transceiver knows the transmission rate, which often varies up and down based upon collisions, interference, competing wireless networks, etc. In other embodiments, the latency, l, is determined at the television  5  (or other base-device) by measuring the time from start of transmission of the packet  57  until start or end of reception of the acknowledgement, then allocating part or all of the time to the latency l. For example, if the transmission packet length is 128 bits and the acknowledgement packet length is 64 bits, and the time measured is 12 microseconds, then ⅔ of the time or 8 microseconds is allocated to the latency l. In such, the latency value is then transmitted as part of the next packet  57 , received by the transceiver  53  and provided to the timing circuit  55  over the latency interface  72  for determining synchronization of the shutters  54 / 56 . 
         [0033]    The timing circuit locks onto the synchronization signal  70  and adds or subtracts the latency value l to generate a left-eye (Q) control signal and a right-eye (−Q) that are coupled to the left-eye shutter  54  and right-eye shutter  56 , respectively, by shutter drivers  60 / 59 . In the preferred embodiment, the timing circuit  55  includes a phased-locked-loop that provides the left-eye and right-eye control signals during a loss of the synchronization signal  70 , for example when interference temporarily disables transmission of the packets  57 . In some embodiments, the phase-locked-loop also performs a filter function, ignoring spurious extreme latency values that occur, for instance, when the wireless interface is used to transfer data, etc. 
         [0034]    In this example, since the latency value is a prediction and has inherent, minor inaccuracies due to interference, distances, reflections, etc, a skew control is provided. Any known skew control device is anticipated such as up/down buttons  61 / 63  (as shown), thumb wheels, rotary controls such as potentiometers, etc. In the example shown, the skew control includes an up-skew  61  and a down-skew  63  which moves the synchronization timing forward or backward, respectively. In such, the user adjusts the skew for maximum viewing enjoyment. 
         [0035]    Referring to  FIG. 5 , an exemplary synchronization timing chart is described. In this example, the alternation of the eye shutters  54 / 56  is intended to occur during the leading edge transition and falling edge transition of the synchronization signal  90  at the television  5 . It is anticipated that when non-three-dimensional content is displayed, a special transmission packet is sent to signal the eyewear  50 A to open both shutters  54 / 56 . 
         [0036]    In one embodiment, the internal television  5  (or other base-device) has an internal synchronization signal  90  that is true (1-value, positive, etc) when left-eye content is displayed on the display  7  and is false (0-value, zero, etc) when right-eye content is displayed on the display  7 . Ideally, the left-eye  54  shutter opens when the internal synchronization signal  90  is true and closes when the internal synchronization signal  90  is false and the right-eye shutter  56  is opens when the internal synchronization signal  90  is false and closes when the internal synchronization signal  90  is true. The television  5  (or other base-device) begins transmission of a synchronization packet  57  at t 0  and the transceiver  53  does not have a completely received and processed packet  57  until t 0 +l. At t 0 +l, the transceiver  53  transitions the output synchronization signal  70  from zero to one to signal the timing circuit  55 . This synchronization signal  70  lags the television&#39;s  5  internal synchronization signal  90  and is not directly used to control shuttering of the left-eye shutter  54  and right-eye shutter  56  because such shuttering would result in blurred images and/or other undesirable artifacts. The eyewear synchronization signal  70  is combined with the latency value l to recreate an eyewear internal synchronization signal  96  that closely aligns with the television  5  internal synchronization signal  90 . In this example, the latency value l is determined during the first synchronization packet  57  transmission at t 0  and is subsequently subtracted from the eyewear synchronization signal  70  to determine the positive transition for the internal synchronization signal  98 . After receiving two synchronization packets at t 0  and t 2 , the timing circuit  55  determines the full cycle time by subtracting t 0 +l from t 1 +l. The timing circuit  55  divides the full cycle time by two to determine the half-cycle time (e.g. the time each shutter  54 / 56  alternate). The timing circuit determines when the leading edge  97  of the internal synchronization signal  96  will occur by subtracting the latency value l from the internal synchronization signal  94  pulse at t 2  and adding one full cycle time. The timing circuit determines when the falling edge  98  of the internal synchronization signal  96  will occur by adding the half cycle time to the time of the leading edge  97 . This sequence continues until any loss of the synchronization packets  57 , at which time, it is preferred, but not required, that the timing circuit include a phase locked loop that locks onto the internal synchronization signal  96  and continues the operation of the shutters  54 / 56  until the synchronization packets  57  are again received. 
         [0037]    The third waveform  94  represents the transmission of an acknowledgement packet from the eyewear  50 A to the television  5 . In general, most wireless protocols use acknowledgement packets to signal the transmitter of successful reception of packets such as the synchronization packet  57 . 
         [0038]    Referring to  FIG. 6 , a first exemplary schematic view of an exemplary television will be described. This figure is intended as a representative schematic of a typical monitor/television  5  and in practice, some elements are not present in some monitors/televisions  5  and/or additional elements are present in some monitors/televisions  5  as known in the industry. In this example, a display panel  7  is connected to a processing element  100 . The display panel  7  is representative of any known display panel including, but not limited to, LCD display panels, Plasma display panels, OLED display panels, LED display panels and cathode ray tubes (CRTs). 
         [0039]    The processing element  100  accepts video inputs and audio inputs selectively from a variety of sources including an internal television broadcast receiver  102 , High Definition Multimedia Interface (HDMI), USB ports and an analog-to-digital converter  104 . The analog-to-digital converter  104  accepts analog inputs from legacy video sources such as S-Video and Composite video and converts the analog video signal into a digital video signal before passing it to the processing element. The processing element controls the display of the video on the display panel  7 . 
         [0040]    Audio emanates from either the broadcast receiver  102 , the legacy source (e.g., S-Video) or a discrete analog audio input (Audio-IN). If the audio source is digital, the processing element  100  routes the audio to a digital-to-analog converter  106  and then to an input of a multiplexer  108 . The multiplexer  108 , under control of the processing element  100 , selects one of the audio sources and routes the selected audio to the audio output and an internal audio amplifier  110 . The internal audio amplifier  110  amplifies the audio and delivers it to internal speakers  134 / 136 . 
         [0041]    The processing element  100  accepts commands from a remote control  111  through remote receiver  113 . Although IR is often used to communicate commands from the remote control  111  to the remote receiver  113 , any known wireless technology is anticipated for connecting the remote control  111  to the processing element  100  including, but not limited to, radio frequencies (e.g., Bluetooth), sound (e.g., ultrasonic) and other spectrums of light. Furthermore, it is anticipated that the wireless technology be either one way from the remote  111  to the receiver  113  or two way. 
         [0042]    The television internal synchronization signal  90  is generated by, for example, the processing element  100 . The processing element  100  determines when a three-dimensional content is being displayed and when left-eye content or right-eye content is being displayed by receiving such indication on an input signal (e.g., HDMI, USB, etc) or extracting such information from the video display signal, for example, a specific set of pixels of each frame dedicated to indicate left-frame or right-frame. The processing element  100  communicates with an RF transceiver  120  to initiate transmission of the synchronization packet  57  at, for example, the start of the left-eye frame. In other embodiments, the processing element  100  communicates with an RF transceiver  120  to initiate transmission of the synchronization packet  57  at the start of each frame and each synchronization packet  57  includes an indication of which type of frame (left-eye or right-eye or two-dimensional) is being displayed. 
         [0043]    In embodiments in which the television computes the latency l, the RF transceiver  120  signals the processing element  100  when an acknowledgement of the synchronization packet  57  is received back from the eyewear  50 A. The processing element  100  then determines the round-trip time from the start of transmission until the receipt of the acknowledgement and allocates a portion of the round-trip time to generate a latency l value. The latency l value is then encoded into the next synchronization packet  57  for use within the receiver  80 / 81  to correctly synchronize to the synchronization packet  57 . In some embodiments, instead of transmitting the latency value to the receiver  80 / 81  within the eyewear  50 A, the processing element  100  uses the latency value l to transmit the synchronization packet  57  earlier than the actual synchronization point so that, under normal conditions, the reception of the synchronization packet  57  by the receiver  80 / 81  coincides with the synchronization point. 
         [0044]    Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result. 
         [0045]    It is believed that the system and method and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.