Could the Tile Format revolutionise 3D broadcasting?

Italian company Sisvel Technology were promoting their 3D frame compatible system, named  “Tile Format”  during the recent European Digital Forum – a backwards compatible format capable of delivering 2D HD and 3D content in one signal.

The Tile Format was created by the researchers of Italian company Sisvel Technology almost three years ago. It arose out of the limitations of existing 3D broadcasting formats, the most common of which is known as Side-by-Side, as used by the likes of Sky 3D, 3net and HIGH TV.

Side-by-Side (SBS) is also described as a ‘frame compatible’ format, as the left and right images are packed within one regular full HD frame by squeezing them both horizontally. The SBS image can be broadcast over existing infrastructures without any license fees as the basic patents already lapsed, being established over 20 years ago. A 3D TV will then de-interlace the video and stretch both the left and right images back to their correct aspect ratios. A passive 3D TV will then divide each image into every other line (line interleaved display) and an active 3D TV will display each frame after another (frame sequential display).

Regardless of the viewing method, the Side-by-Side format results in a 50% loss in horizontal resolution due to both images being squeezed into the space of one frame.

In addition to the drop in picture quality, the Side-by-Side format as it is delivered today, is not capable of delivering a 2D HD quality image. Therefore, an extra channel (and extra bandwidth) is required for 2D broadcasting if a platform operator wants to offer its viewers HD 2D programming in simulcast with 3D. 

Sisvel Technology claims to have solved both the resolution and bandwidth problems with its Tile Format and Cropping Rectangle method that can deliver a 2D HD and 3D image: two left and right 720P images for HD 3D video and one of the two for the 2D TV sets with an optional depth map for 3D depth control, all in one signal, compatible with existing broadcast infrastructures.
The Tile Format can be encoded within the existing MPEG2 and MPEG4 standards; the latter provides a metadata called “Cropping Rectangle” that  can ensure existing 2D TVs would only see the 2D image while 3D TVs could process the 3D image, negating the need for broadcasters to duplicate channels to broadcast the same content in 2D and 3D.

In other words, existing HD legacy decoders, without any change of the firmware, can provide a 2D HD compatible picture, while they only need a simple firmware upgrade from the manufacturer in order to be able to feed a 3D display.

This could make the Tile Format very appealing for terrestrial platforms like Freeview in the UK, especially as quantity of 3D content is still limited making the launch of an entire 3D channel unfeasible. Using the Tile Format, terrestrial platform operators could alert viewers that a 3D version of a programme was available at the click of a button (for example “Press red to watch this presentation is 3D”).

How it works

Two 720p frames are packed within a single 1080p frame in an innovative way by splitting the right image into three (as shown).

One 720P picture occupies the space intact, but because there is no physical room for another entire picture, the other image is divided into three pieces. The home decoder then reassembles the second picture. The remaining black part can be used for additional information like a depth map.

The video source, therefore, can be either 3D stereoscopic or 2D HD, live or from file based playout system. In a live TV scenario, a stereo source is fed to a real time ‘panelizer’ that composes the Tile Format. The panelizer is the hardware that divides the right frame into its three sub-divided parts and then assembles the composite frame. The output from the panelizer (that is a plain HD video stream) is fed to a master control used to switch between a plurality of HD video sources which is then sent out for broadcast. One hardware panelizer has been designed by the Italian company BLT, a high professional video equipment manufacturer.

The output from the master control is then compressed with an encoder; in case of an H.264/AVC encoder it is possible to set the Cropping Rectangle parameter to take only one of the two stereoscopic images and to support the usage of the SEI signalling for identifying the stereo arrangement, enabling the broadcaster to signal the Tile Format to suitable decoders and to provide backward compatibility with 2D receivers.

Finally on the users' premises, a DVB-T/S set top box or a TV receives the stream and decodes the video. In case of a 3D external decoder, it can drive the TV in 3D mode by converting the Tile Format to one of the main Frame Packing modes (1280x1470p50, that is a double 720p,  mode), defined by the HDMI specification.

Despite being launched almost three years ago, the uptake for the Tile Format has been limited, but this may not be surprising because the previous system took 20 years before being taken into consideration. Sisvel is currently forming a network between broadcasters and content producers and pushing the technology forward within the international standardisation bodies, mainly the DVB and the MPEG video-encoding group.

In Italy, broadcasters in Turin and Tuscany have begun trials of the Tile Format system. QuartaRete TV, a local Italian TV station broadcasting from Piedmont, was the first to broadcast free-to-air backward compatible HD 3D stereoscopic TV programs in November 2010.

Quartarete’s daily 3D broadcasts include documentaries and events including sport and music. “3D is proving especially effective for tele-sales including real estate,” says Davide Boscaini Managing Director of Quartarete. 50 Canale TV in Tuscany also uses the Tile Format. VTV Broadcom is ready to trial the Tile Format in Vietnam, starting presumably next August.

In May 24th 2011 SES started transmitting a 3D Tile Format demo channel on the ASTRA 19.2° satellite, allowing the Tile Format to be received throughout all Europe. The “3D Tile Format” channel is operational four hours a day and features a range of 3D programmes from the genres of travel & culture, technology, art & music and sports. You can watch the clips here.

 

Barriers to take up might be because existing 3D TVs from the likes of Samsung and LG do not offer a Tile Format viewing option. Sisvel do not believe this will be an issue however saying: “Upgrading the software for the TVs will not be a major investment for the manufacturers. In this respect, we can support them with all the technical details they need in order to address the software development”.

Also, HD broadcasters like Sky HD, present HD programming in the 1080i format, a different type of resolution than 720P (the first one is interlaced, the second one is progressive), and it is unlikely the likes of Sky would want to change their HD picture format to deliver 2D and 3D content in the same stream, especially now that they have ample bandwidth. However, Tile format would allow them to increase the picture quality of the 3D broadcasting. 

Other channels such as 3net and HIGH TV have also adopted the Side-by-Side format, but Vittorio Giovara, Television Project Engineer from Sisvel Technology, told 3D Focus that he expects the Tile Format to be more appealing for terrestrial broadcasts and why the format will come into its own with future 3D panels.

One additional feature of the Tile Format is the lower right square: when the last tile is empty (eg. always black), the overall bandwidth required is lowered by 1/9, as the compression ratio is improved by the constant video section.

Alternatively it could be possible to reuse the remaining space by inserting a depth map of the broadcasted stereo pair: in this way, future decoders will be able to extract precise depth information automatically from the frame compatible picture, useful to properly place on-screen graphical controls (such as volume, channel info and other menus) at right depth, without corrupting the image or spoiling the stereo experience of the users. Also, it might be possible to offer the user to control the depth of the image, since using the depth map the TV set can build up an intermediate view between the broadcasted L and R views. 

For more information visit http://www.sisveltechnology.com/3D_tile_format.asp

 

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