Abstract:
The present disclosure relates to a method for transmitting two consecutive pairs of images. The method may include decimating each image with a ratio of 2, assembling the two decimated images of each pair in a composite image, transmitting the composite images, and reconstructing complete images from the composite images. In decimation, the information removed from the images of the first pair may be kept in the images of the second pair, from the spatial point of view, and the complete images may be reconstructed by de-interlacing processing from the composite images.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to transmission of three-dimensional (3D) video streams on legacy transport infrastructures for transmitting two-dimensional (2D) high-definition video streams. 
     BACKGROUND OF THE INVENTION 
     The new High-Definition Multimedia Interface (HDMI) standards (versions 1.4 and 1.4a), defining an interface for transmission of decoded programs to final player equipment, provide for transfer of full-resolution high-definition 3D video streams, i.e. transfer of two stereoscopic full-resolution HD views, which doubles the transmission pass band. This pass band is not available on current transport infrastructures (satellite, DTTV, cable). 
     Pending a transport infrastructure dedicated to 3D programs, the interested parties and normalization committees (DVB, HDMI, MPEG) are working on approaches enabling 3D video to be transmitted on existing transport infrastructures. The progress is published on the Websites of these committees. It is sought to insert two views in place of each image in the transported stream and, by way of minor modifications to the reception equipment, to reconstruct the two views in a format compatible with the HDMI standard. As existing transport infrastructures are not designed for this, the resolution of the views may have to be downgraded. 
     Among the different transport formats that have been reviewed, two generic candidates have been identified: Top-and-Bottom (TaB) and Side-by-Side (SbS). Each of these generic formats can be combined with an existing 2D high definition (HD) format of the progressive type, i.e. the 50 Hz and 60 Hz variants of the 720p format and the 1080p format at 24 Hz. Only the SbS generic format is combined with the 50 and 60 Hz variants of the 1080i interlaced format. 
       FIG. 1 a    represents an HD image according to the TaB format, i.e. a composite image. The top half of the image comprises the left stereoscopic view L at half the vertical resolution, and the bottom half comprises the right stereoscopic view R, also at half the vertical resolution. 
       FIG. 1 b    represents an HD image, also composite, according to the SbS format. The left half of the composite image comprises the left stereoscopic view L at half the horizontal resolution, and the right half of the composite image comprises the right stereoscopic view R, also at half the horizontal resolution. 
       FIGS. 2 a  to 2 c    illustrate decimation matrices that have been proposed for reducing the resolution of the stereoscopic images so as to be able to transport the latter in TaB or SbS format. 
     The complementary matrices of  FIG. 2 a    enable one line out of two to be kept to create an image in TaB format (FIG.  1   a ). The top matrix keeps the odd lines and the bottom matrix keeps the even lines. 
     The complementary matrices of  FIG. 2 b    enable one column out of two to be kept to create an image in SbS format ( FIG. 1 b   ). The top matrix keeps the odd columns and the bottom matrix keeps the even columns. 
     The matrices of  FIG. 2 c   , called quincunx (checkerboard) matrices, enable one pixel out of two to be kept per line and per column. In the top matrix, the process starts from a pixel in the top left corner. The bottom matrix defines the complementary decimation. The pixels kept by application of these matrices are compacted by lines for the TaB format or compacted by columns for the SbS format. 
     There appears to be no consensus on the choice of decimation matrices. The CableLabs consortium is the first to propose a choice in the document OpenCable Specifications, Content Encoding Profiles 3.0 Specification, C-SP-CEP3.0-I01-100827, section 10.2, sub-paragraph #6, published on their Website on Aug. 27, 2010. It proposes using the same matrix for all the images, more precisely one of the matrices of  FIG. 2   a.    
       FIG. 3  schematically illustrates an example of a reception chain of TaB composite images. The composite images  10  reach a vertical interpolator  12  at the refresh frequency, for example, 60 Hz. The interpolator completes the left half-resolution image L of the composite image with the missing lines and then does the same with the right half-resolution image R. The interpolator works at twice the refresh frequency (120 Hz) and supplies the two obtained, left and right, full-resolution HD images to an HDMI transmission circuit  14  at this frequency. Circuit  14  assembles the left and right images into a double-resolution image  16 , for example, of double height, and transmits the latter at the initial refresh frequency (60 Hz) to a 3D display. To process SbS composite images, interpolator  12  would be replaced by a horizontal interpolator completing the half-resolution images with the missing columns. It is noteworthy that these transmission techniques divide the spatial resolution of the stereoscopic views by 2. 
     SUMMARY OF THE INVENTION 
     An approach is disclosed whereby the spatial resolution of the stereoscopic views transported on a legacy infrastructure can be enhanced. 
     A method is provided for transmitting two consecutive pairs of images and may comprise decimating each image with a ratio of 2, assembling the two decimated images of each pair in a composite image, transmitting the composite images, and reconstructing complete images from the composite images. In decimation, the information removed from the images of the first pair are kept in the images of the second pair, from the spatial point of view, and the complete images are reconstructed by de-interlacing processing from the composite images. 
     According to one embodiment, the information removed by decimation from the first image of a pair is kept, from the spatial point of view, in the second image of the pair. 
     According to one embodiment, decimation removes the lines of a first parity in the first image of a first of the two pairs, the lines of a second parity in the second image of the first pair, the lines of second parity in the first image of the second pair, and the lines of first parity in the second image of the second pair. 
     Other advantages and features will become more clearly apparent from the following description of particular embodiments of the present disclosure given for non-restrictive example purposes only and represented in the appended drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 a  and 1 b    illustrate two proposed image formats for transporting stereoscopic images on prior art infrastructures; 
         FIGS. 2 a  to 2 c    illustrate proposed decimation matrices to reduce the spatial resolution of the stereoscopic images to be transported according to the formats of  FIGS. 1 a    and  1   b;    
         FIG. 3 , described in the above, represents a processing chain, on reception, of transported images according to the format of  FIG. 1 a   , according to the prior art; 
         FIGS. 4 a  to 4 d    represent particular combinations of the parities of the lines or columns used in two consecutive composite images, which, with adequate processing, may enable the spatial resolution to be substantially enhanced, according to the present invention; and 
         FIG. 5  is a schematic diagram of a processing chain designed to make use of the composite images of  FIGS. 4 a  and 4 b   , according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In order to increase the spatial resolution of images that have been decimated, in particular, to transport the latter on a legacy infrastructure, it is disclosed to use de-interlacing techniques rather than spatial interpolation techniques. De-interlacing techniques do in fact enable spatial information to be retrieved, from two consecutive frames, on account of the fact that the missing lines in one frame are found in the following frame with a temporal offset. 
     For this purpose, consecutive composite images, even if they originate from decimation of progressive images, are made to conform to an interlaced video stream. 
       FIGS. 4 a  to 4 d    illustrate combinations of possible parities of lines or columns in the previously described composite image formats, enabling an interlaced video stream to be reproduced. The combinations of parities affect two consecutive composite images, which thereby become two consecutive frames of an interlaced stream. 
       FIG. 4 a    illustrates two consecutive composite TaB images conformed in two consecutive frames. The top half of the first frame (on the right) includes the odd lines (suffix “ 1 ”) of the corresponding first left view L. The bottom half of this frame includes the even lines (suffix “ 0 ”) of the corresponding first right view R. 
     The second frame (on the left), constructed by decimation of a second pair of stereoscopic views, includes the lines that are missing, from the spatial point of view, from the first frame. In other words, the top half of the frame includes the even lines (suffix “ 0 ”) of the second left view L. The bottom half of the frame includes the odd lines (suffix “ 1 ”) of the second right view R. 
       FIG. 4 b    corresponds to an alternative embodiment of  FIG. 4 a   . Instead of using different parities in the top and bottom halves of each frame, the same parity is used. The first frame thus includes the odd lines of the first pair of left and right views and the second frame includes the even lines of the second pair of left and right views. 
       FIG. 4 c    illustrates the combination of parities of  FIG. 4 a    applied to SbS composite images. In other words, the left half of the first frame includes the odd columns of the first left view, and the right half of the first frame includes the even columns of the first right view. The left half of the second frame includes the even columns of the second left view, and the right half of the second frame includes the odd columns of the second right view. 
       FIG. 4 d    illustrates the combination of parities of  FIG. 4 b    applied to SbS composite images. In other words, the first frame includes the odd columns of the first pair of left and right views, and the second frame includes the even columns of the second pair of left and right views. 
     For streams formatted according to  FIGS. 4 a  and 4 b   , vertical de-interlacing may be used, of the type used for conventional interlaced streams. For streams formatted according to  FIGS. 4 c  and 4 d   , horizontal de-interlacing may be performed. To achieve this, the vertical de-interlacing techniques may simply be transposed. 
     The de-interlacing principles can also apply if quincunx decimation matrices are used ( FIG. 2 c   ). Views decimated by way of these matrices can be transported in either of the TaB and SbS formats, according to the compacting direction of the pixels. The parities  1  and  0  used in  FIGS. 4 a  to 4 d    then respectively identify the first and second matrices of  FIG. 2 c   . Diagonal de-interlacing may be operated on the frames constituted in this way. Variants of complementary parity to each of the  FIGS. 4 a  to 4 d    are naturally available. 
       FIG. 5  schematically illustrates a processing chain that can be suitable for processing an interlaced stream according to the formats of  FIGS. 4 a  and 4 b   . Such a processing chain may be available in typical HD reception equipment, in particular to process the 1080i format. According to this format, each frame includes 540 lines and the parity of the lines alternates from one frame to the next. 
     Frames  10 ′, represented according to the format of 
       FIG. 4 a   , arrive at a frequency of 60 Hz, for example, on a vertical de-interlacing circuit  18 . This circuit performs de-interlacing on two consecutive frames, for example (the number of frames on which de-interlacing is performed, and therefore the number of frames that circuit  18  stores in advance, depends on the technique used). Among the available de-interlacing techniques, the following may be used: reverse film mode using film mode detection techniques, motion adaptive de-interlacing, and motion compensated de-interlacing. De-interlacing is first performed on the top halves of the consecutive frames, for example, to produce a progressive full-resolution left image, and then on the bottom halves of the consecutive frames to produce a progressive full-resolution right image. These two full-resolution images are produced at twice the refresh frequency, here at 120 Hz. As in  FIG. 3 , these images are then processed by an HDMI transmission circuit  16 . 
     De-interlacing circuit  18  is typically intended to process frames of 540 lines at the most, to produce progressive images of 1080 lines at the refresh frequency rate, here 60 Hz. To process frames according to  FIGS. 4 a  and 4 b   , it would process 720-line frames and produce images at twice the frequency. It would further be configured to produce a full-resolution image from each half frame it receives. In fact, these operational details can most of the time be dealt with in software by updating the firmware of existing equipment intended for 2D HD video reception. 
     This approach, with the frame formats of  FIGS. 4 a  and 4 b   , thereby enables 3D HD programs with a quality between full resolution and half-resolution to be transmitted on existing transport infrastructures, and enables these programs to be viewed on existing reception equipment (through a simple firmware update in a large number of cases). The display equipment should of course be 3D video-capable. 
     To process frames according to the formats of  FIGS. 4 c  and 4 d   , the circuit  18  would be designed to perform horizontal de-interlacing. This is no more complex than vertical de-interlacing, but it is likely that existing reception equipment will not be able to do this through a simple firmware update. 
     The formats of  FIGS. 4 c  and 4 d    may in particular be used to transport a 3D video stream in SbS 1080i format. In this case, circuit  18  performs horizontal de-interlacing to reconstitute the left and right views in full horizontal resolution in 1080i format. The circuit  18  may simultaneously perform conventional de-interlacing to obtain a 1080p format. Vertical de-interlacing can also be delegated to a conventional de-interlacing circuit often provided downstream from the HDMI interface, for example in a television set. 
     To process frames where decimation has been performed using the quincunx matrices of  FIG. 2 c   , circuit  18  would be designed to perform diagonal de-interlacing. 
     Among the formats of  FIGS. 4 a  to 4 d   , the formats of  FIGS. 4 a  and 4 c    are preferred, i.e. where the parities of information of the left and right views of a frame are opposite. This enables an exact full-resolution image to be constructed, when the left and right views corresponding to a frame are spatially correlated, by combining the odd lines of the left view and the even lines of the right view (or vice-versa).