Abstract:
A temporal alignment system and method divides and transports video frames and uses average picture level in determining whether data sets within a particular frame are misaligned.

Description:
PRIORITY CLAIM AND INCORPORATION BY REFERENCE 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/217,523 filed Sep. 11, 2015 which is incorporated herein by reference in its entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Broadcast and production signal transport requiring original signal division and multilink transport is in a protracted infancy. Reasons include lack of proven equipment and movie and television industry reluctance to develop, implement, and use equipment capable of transporting ultra-high definition signals such as or similar to 4K signals (see e.g., DCI 4K, UHDTV, UHD-1, UHD 4K, 4K). 
       Field of Invention 
       [0003]    This invention relates to the electrical and process arts. In particular, a system and method for enhancing temporal signal alignment. 
       Discussion of the Related Art 
       [0004]    While temporal signal alignment is well known in some applications, temporal signal alignment and realignment in the context of 4K images transported over multiple lines is not well known. Further, temporal signal alignment systems operating in a 4K environment without the use of time stamps embedded in the signal are to the author&#39;s knowledge unknown. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a temporal alignment system and method. Various embodiments may be used in connection with determining whether frames, panes, signals, and/or data sets are aligned. 
         [0006]    In an embodiment, a system for detecting temporal misalignment in video frames that are divided for transport, the system comprises: a signal divider for dividing a single signal S into N signal portions S 1  . . . S N ; each signal portion for carrying a portion of the same video frame; N transport links, each link for receiving a respective signal Sx from the signal divider and for delivering a signal Sx′ to a signal reassembler (1≦x≦N); the signal reassembler for selectively reassembling signal portions S 1 ′ . . . S N ′ corresponding to S 1  . . . S N  into a single signal S′; and, a misalignment monitor colocated with the signal reassembler; wherein the monitor utilizes information inherent in the signal portions S 1 ′ . . . S N ′ to detect whether temporal frame misalignment has occurred. 
         [0007]    In some embodiments, the system above and one or more of i) wherein the signals are Serial Digital Interface signals for transmitting 4K video, wherein N=4, further comprising a facility of the monitor for evaluating average picture level for each of signal portions S 1 ′ . . . S N ′ and wherein the monitor facility for evaluating average picture level is used in determining whether a temporal frame misalignment has occurred and used in correcting a discovered temporal frame misalignment, iv) further comprising a facility of the monitor for evaluating average picture level for each of signal portions S 1 ′ . . . S N ′ and wherein changes in average picture level caused by one or more scene cuts are used in determining whether a temporal frame misalignment has occurred, v) further comprising a facility of the monitor for evaluating average picture level for each of signal portions S 1 ′ . . . S N ′ and wherein temporal alignment of changes in average picture level among the signal portions is used to determine whether a temporal frame misalignment has occurred, and vi) further comprising a facility of the monitor for evaluating average picture level for each of signal portions S 1 ′ . . . S N ′ and wherein temporal alignment of discontinuities in average picture level among the signal portions S 1 ′ . . . S N ′ is used to determine whether temporal frame misalignment has occurred. 
         [0008]    In an embodiment a video frame temporal misalignment detection method comprising the steps of: providing a 4K video camera for acquiring images, each image contained in a video frame that is divisible into 4 panes; from one or more camera outputs, deriving 4 SDI signals corresponding to respective video frame panes; the SDI signals transporting the video frames over respective links such that during transport a pane of a particular frame is temporally misaligned and appears as a pane of another frame; providing a misalignment monitor with a facility for monitoring average picture level of each of the SDI signals; and, determining a temporal misalignment event has occurred when average picture level changes fail to occur simultaneously. 
         [0009]    In some embodiments, the method above and one or more of the steps i) wherein the monitor is configured to detect changes in average picture level arising from scene cuts, wherein each pane of a frame is a one quarter slice of the image, wherein each pane of a frame reproduces the image at a reduced resolution, and providing a frame reassembler coupled to the links and the monitor and wherein upon discovery of a video frame temporal misalignment event the monitor causes the reassembler to correct the misalignment by time shifting reassembler data received from at least one of the derived SDI signals. 
         [0010]    In an embodiment, method for finding misaligned data sets comprising the steps of: dividing a 4K video signal for transport along 4 SDI links; transporting the 4K video signal along the SDI links; near a transport terminus, comparing temporal alignment of an average picture level discontinuity in each SDI link; and, finding a temporal correction is needed when the discontinuities are not substantially temporally aligned. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention is described with reference to the accompanying figures. The figures, incorporated herein and forming part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art to make and use the invention. 
           [0012]      FIG. 1  shows a multi-link signal transport system of the present invention. 
           [0013]      FIG. 2  shows a source with signal division for use with the system of  FIG. 1 . 
           [0014]      FIG. 3A  shows a 4K image. 
           [0015]      FIG. 3B  shows a square division quad split of the image of  FIG. 3A . 
           [0016]      FIG. 4A  shows a 4K image. 
           [0017]      FIG. 4B  shows an interleaved or two sample interleave of the image of  FIG. 4A . 
           [0018]      FIG. 5  shows an exemplary multi-link signal transport system with temporal alignment monitoring. 
           [0019]      FIG. 6A  illustrates temporally aligned signal transport  600 A. 
           [0020]      FIG. 6B  shows an exemplary inherent temporal alignment assessment method. 
           [0021]      FIG. 7A  illustrates temporally misaligned signal transport  700 A. 
           [0022]      FIG. 7B  shows an exemplary inherent temporal misalignment assessment method. 
           [0023]      FIG. 8  shows another embodiment of the multi-link signal transport system with temporal alignment monitoring of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The disclosure provided in the following pages describes examples of some embodiments of the invention. The designs, figures, and descriptions are non-limiting examples of certain embodiments of the invention. For example, other embodiments of the disclosed device may or may not include the features described herein. Moreover, disclosed advantages and benefits may apply to only certain embodiments of the invention and should not be used to limit the disclosed inventions. 
         [0025]    Where parts are connected, descriptions herein using the words “coupled,” “connected,” or “interconnected” refer to either direct or indirect connections. Direct connections provide for a first part connected directly to a second part, for example A connected directly to B. Indirect connections provide for a first part connected indirectly to a second part, for example A connected indirectly to C via B. 
         [0026]      FIG. 1  shows a multi-link signal transport system  100 . As seen, a transport block  112  interconnects a source block  102  and a destination block  122 . 
         [0027]    In the source block  102 , a signal such as an image signal is divided among four signal outputs s 1 -s 4 . In an embodiment, the source block includes a video camera that i) acquires a 4K or similar image and provides multiple output signals s 1 -s 4  that may be combined to reproduce the acquired 4K image. 
         [0028]    Signals such as image signals transported from a source  102  to a destination  122 , which may be and/or include a reassembler, can be divided at the source, transported via links, and reassembled at the destination. For example, where a 4K image is transported  112 , it may be transported via multiple HD-SDI links. In particular, four (4) HD-SDI links  114  at 3 Gb/s might be used where each link carries one quarter (¼) of the 4K image information. As shown, signals s 1 -s 4  from the source  102  are transported via links  114  and arrive at the destination  122  as signals s 1 ′-s 4 ′. 
         [0029]    Notably, to the extent that signals s 1 -s 4  are transported  112  with temporal and content fidelity, then signals s 1 ′-s 4 ′ may be reassembled to reproduce a 4K image that was acquired by the camera. However, it is not always the case that fidelity is maintained. In particular, loss of temporal fidelity may occur due, for example, to varying signal transit times among the transport links  114 . 
         [0030]      FIG. 2  shows a source with signal division  200 . Where content such as 4K imagery is captured via a device such as a digital video camera, the content may be readied for transport by multiple links as described above. For example, imagery captured is a source capture block  202  results in a signal “s” that is fed  203  to a source outputs block  212 . The four square checkerboard icon with all four blocks marked indicates a full bandwidth 4K signal. 
         [0031]    In the source outputs block  212 , the 4K signal is repackaged for transport by four links. At a first output  213 , a signal s 1  provides ¼ of the 4K bandwidth and carries % of the 4K content as indicated by the top left block of the checkerboard icon. At a second output  215 , a signal s 2  provides % of the 4K bandwidth and carries % of the 4K content as indicated by the top right block of the checkerboard icon. At a third output  217 , a signal s 3  provides % of the 4K bandwidth and carries % of the 4K content as indicated by the bottom right block of the checkerboard icon. At a fourth output  219 , a signal s 4  provides % of the 4K bandwidth and carries % of the 4K content as indicated by the bottom left block of the checkerboard icon. 
         [0032]    Signals such as images and 4K images in 4K camera video can be carried by multiple links as described above.  FIGS. 3A-B ,  4 A-B illustrate two types of signal or image division enabling multilink transport. 
         [0033]      FIG. 3A  shows a 4K image  300 A and  FIG. 3B  shows a square division quad split  300 B of the image of  FIG. 3A . In particular, the image of  FIG. 3A  is divided into four image portions, each image portion reproducing or indicating a ¼ share of the original 4K image. Pane  1  is upper left, pane  2  is upper right, pane  4  is lower right, and pane  3  is lower left. As skilled artisans will appreciate, reproduction of the original 4K image from a group of 4 panes representing a single frame requires temporal alignment of the panes. 
         [0034]      FIG. 4A  shows a 4K image  400 A and  FIG. 4B  shows an interleaved or two sample interleave of the image  400 B of  FIG. 4A . As in  FIGS. 3A-B , the 4K image is divided into 4 panes. But, here, each pane carries the whole image at % of its original resolution. This method is referred to as interleaving, here a  2  sample interleave. For example, pane  1  is the whole image with 0-25% of the content, pane  2  is the whole image with 26-50% of the content, pane  3  is the whole image with 51-75% of the content, and pane  4  is the whole image with 76-100% of the content. 
         [0035]      FIG. 5  shows an exemplary multi-link signal transport system with temporal alignment monitoring  500 . As seen, a transport block  512  interconnects a source block  502  and a destination block  522 . 
         [0036]    In the source block  502 , a signal such as an image signal is divided among four signal outputs s 1 -s 4 . In an embodiment, the source block includes a video camera that i) acquires a 4K or similar image and provides multiple output signals s 1 -s 4  that may be combined to reproduce the acquired 4K image. 
         [0037]    As described above, signals such as image signals transported from a source  502  to a destination  522  can be divided at the source, transported via links, and reassembled at the destination. Signal processing such as compression may occur at a first signal processor  511  and signal processing such as decompression may occur at a second signal processor  513  (e.g., JPEG 2000, 11264). In some embodiments, the compression and decompression method provides for a lossless data transfer. 
         [0038]    Signals s 1 -s 4  from the source  502  are transported via links  114  and arrive at the destination  522  as signals s 1 ′-s 4 ′. Notably, to the extent that signals s 1 -s 4  are transported  512  with temporal and content fidelity, then signals s 1 ′-s 4 ′ may be combined to reproduce a 4K image that is a replica or near replica of the image acquired by the camera. However, it is not always the case that temporal fidelity is maintained. In particular, loss of temporal fidelity may occur due, for example, to varying signal transit times among the transport links  114 . 
         [0039]    As shown, the transported signals s 1 ′-s 4 ′ are inputs to a monitor or monitoring block  532 . The monitoring block provides a means for determining temporal alignment and/or temporal misalignment of signals s 1 ′-s 4 ′. In some embodiments, the destination block  522  and monitor block may be collocated and/or packaged in a common main (as in a rack) or sub (as in a chassis enclosure) housing. In some embodiments the packaged destination  522  and monitor  532  blocks may be referred to as a receiver  542 . 
         [0040]      FIG. 6A  illustrates temporally aligned signal transport  600 A. As seen, signals s 1 -s 4  load frames  1 ,  2  for transport  610 . Each frame is divided for transport along four links  614 . 
         [0041]    At the transport input, frame  1  includes four temporally aligned data sets resulting from dividing a first signal such as a 4K signal. Frame  2  includes 4 temporally aligned data sets resulting from dividing a second signal such as a 4K signal. 
         [0042]    At the transport output, frame  1 ′ includes the four temporally aligned data sets that were input as frame  1  and frame  2 ′ includes the four temporally aligned data sets that were input as frame  2 . 
         [0043]    Methods of monitoring the temporal alignment illustrated in  FIG. 6A  include time stamp methods where information added, i.e., the “time stamp,” to the content being transported provides a basis for assessing temporal alignment. 
         [0044]    Another temporal alignment assessment method does not require that information be added. Rather, information inherent in the content provides a basis for assessing temporal alignment. One or both of inherent and non-inherent assessment methods may be used in the temporal alignment monitor  532  of  FIG. 5 . 
         [0045]    Corresponding to  FIG. 6A ,  FIG. 6B  shows an exemplary inherent temporal alignment assessment method  600 B. For each of four links and link signals s 1 -s 4  values of average picture level (“APL”) are plotted against a common time axis. In an embodiment, average picture level is an average level of the picture signal. In an embodiment, average picture level is the average level of the picture signal during active scanning time integrated over a frame period. APL may be defined as a percentage of the range between blanking and reference white level. In some embodiments, any consistently used measure of APL suffices (see e.g., IDMS 1.03 Information Display Measurements Standard (IDMS), pre-gamma APL (Type 1 APL) for gamma corrected input signal(R, G, B) and post-gamma APL (Type 2 APL) for gamma de-corrected panel display signal(R′, G′, B′)). 
         [0046]    As the plots show, APL data on each of the links (APLs 1  . . . APLs 4 ) indicates a change or discontinuity in average picture level such as an APL change associated with a scene cut. Moreover, this change in APL occurs simultaneously, at time t 1 , for all of the links. 
         [0047]    Monitoring this information, temporal alignment of changes or discontinuities, provides a method of finding when data on multiple links representing a particular frame is not temporally aligned. Notably, this telltale sign of temporal misalignment is part of the picture content and thus is inherent in the signals being transported. 
         [0048]      FIG. 7A  illustrates a signal transport that is temporally misaligned  700 A. As seen, signals s 1 -s 4  load frames  1 ,  2  for transport  710 . Each frame is divided for transport along four links  714 . 
         [0049]    At the transport input, frame  1  includes four temporally aligned data sets resulting from dividing a first signal such as a 4K signal. Frame  2  includes 4 temporally aligned data sets resulting from dividing a second signal such as a 4K signal. 
         [0050]    At the transport output, frame  1 ′ includes three temporally aligned data sets that were input as frame  1  and one temporally misaligned data set  731 . Frame  1 ′ is therefore temporally misaligned, for example because the frame excludes data it should include or includes input data sets from different input data frames. In similar fashion, frame  2 ′ is temporally misaligned, for example because it includes a misaligned frame  733 . 
         [0051]    Corresponding to  FIG. 7A ,  FIG. 7B  shows an assessment of temporal alignment  700 B. For each of four links and link signals s 1 -s 4  values of average picture level (“APL”) are plotted against a common time axis. 
         [0052]    As the plots show, APL data on each of the links (APLs 1  . . . APLs 4 ) indicates a change or discontinuity in average picture level such as an APL change associated with a scene cut. As the plots show, APL data on each of the links (APLs  1  . . . APLs 4 ) indicates a change or discontinuity in average picture level such as an APL change associated with a scene cut. 
         [0053]    For three of the links, APLs 1 , APLs 3 , APLs 4 , the change in APL occurs simultaneously, at time t 1  and corresponds with a first discontinuity, for example a scene cut, such as scene cut  1 . 
         [0054]    For one of the links, APLs 2 , the change in APL occurs at a different time t 2  corresponding with a second discontinuity such as scene cut  2  where t 2 −t 1 =dt. 
         [0055]    Monitoring this information, temporal alignment of changes or discontinuities, provides a method of finding when data on multiple links representing a particular frame is not temporally aligned. Notably, this telltale sign of temporal misalignment is part of the picture content and thus is inherent in the signals being transported. 
         [0056]      FIG. 8  shows another embodiment  800  of the multi-link signal transport system with temporal alignment monitoring of  FIG. 5 . 
         [0057]    In an embodiment, a first signal line  551  interconnecting the monitor and transport blocks  532 ,  512  enables the monitor block to realign data sets along links such that data sets within frames are aligned. Control function capabilities include speeding or slowing transport throughput on any one or more of the links  514 . 
         [0058]    In an embodiment, a second signal line  553  interconnecting the monitor and source blocks  532 ,  502  enables the monitor block to realign data sets along links such that data sets within frames are aligned. Control function capabilities including speeding or slowing source data rates along any one or more of the data source outputs. 
         [0059]    The appendix to this application provides descriptions of similar and/or other embodiments of the present invention. 
         [0060]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the art that various changes in the form and details can be made without departing from the spirit and scope of the invention. As such, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and equivalents thereof.