‘3D Tile’ Broadcasting Technology Would Require New Receivers
3D Tile, the 3D broadcasting technology that Sisvel, an Italian company, plans to showcase at next month’s IFA show in Berlin (CED July 16 p7), builds on the company’s previous work with another Italian company, 3DSwitch. That collaboration produced a system that lets a TV set recognize the 3D format in which source material was coded, while detecting whether viewers are wearing 3D glasses. So a 3D TV can automatically show 2D content when viewers aren’t wearing stereographic glasses, and it immediately switches to 3D when viewers put the glasses on.
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3D Tile allows the storage of two HD frames in a single HD frame, without the compression currently used to squeeze left- and right-eye images into a TV frame, Sisvel said. This is done by using 1080p transmission to carry 720p 3D, it said. But broadcasters would need to make transmission changes to use 3D Tile and only the newest receivers could handle the changes, we've found.
Current “frame packing” of 3D broadcasts in side-by-side or top-bottom formats are “frame-compatible": They work with existing broadcast channels and receivers and need only a new 3D TV for reception. The downside, Sisvel says, is that when the images are anamorphically squeezed side by side, or one above the other, the horizontal and vertical resolutions are different. If the compression is done electronically by discarding pixels, in a staggered “quincunx” pattern, the balance between horizontal and vertical resolution is preserved, but there is loss of diagonal resolution. “Edges look somewhat jagged,” Sisvel says.
3D Tile leaves the left-eye image whole and untouched and slices the right-eye image into small tiles -- usually three -- that are jigsawed around the whole image, Sisvel says. If the original left- and right-eye images are in 720p resolution, everything can be made to fit inside a single 1080p frame, it says. So when the receiver rebuilds the left- and right-eye images there is no loss of 720p resolution, it says. And since one of the two images never altered, the signal can also be made “service-compatible” for showing 2D on 2D TVs, it says.
Encoding is by standard H.264 compression, with metadata in the bitstream to define the way one image has been sliced and should be rebuilt in the receiver, Sisvel says. The company says “existing H.264 decoders, without any change of the firmware, can provide a 2D compatible picture” and need only “a very simple firmware upgrade (through downloading) in order to be able to feed a 3D display."
We asked Sisvel to explain this claim, since broadcast services carry 720p or 1080i signals, not the 1080p signals that 3D Tile requires. We also asked how current receivers designed for 720p and 1080i signals will cope. “From the point of view of a broadcaster,” responded a Sisvel spokeswoman, “recent compression tests performed by the European Broadcasting Union demonstrate that the bitrate needed to broadcast the 1080p 50 fps format equals the bitrate needed for the 1080i 25 fps format.” She said that 1080p 50/60 fps H.264 encoders “are now widely available from all the manufacturers.” As for decoding, most Full HD 1080p TV sets marketed since 2008 “are already equipped with an internal 1080p 50/60 fps H.264 decoder,” the spokeswoman said.
A recent EBU technical document says 1080p/50 “may be used for future broadcasting.” The same document also warns that although 1080p displays “can normally display 1080p/50 images … consumers will need a new set-top-box that can decode MPEG-4 H.264 … to show the benefit of 1080p/50 on their 1080p display.” So only the latest receivers will be able to handle 3D Tile, according to the EBU document.