By David Wood, EBU
3DTV has taken steps forward. The DVB specification for ‘Phase 1’ 3DTV was approved by the DVB Steering Board in February 2011. It can be downloaded now from the DVB website.
Phase 1 is a system that does not need a new home set-top box (though it could also be used if there was a new set-top box). This is a ‘Frame Compatible ‘system. The Left and Right images needed by the 3D display are ‘spatially multiplexed’ to ‘look like’ a normal HDTV image to the set-top box. The set-top box passes the combined image to the display, where the two pictures are unraveled, and displayed so they can be viewed with 3D glasses.
The price for making the two Left and Right images look collectively like an HDTV picture is that they have to ‘share’ the HDTV resolution, though the 3DTV results are still very good quality.
The DVB specification asks display makers to allow for eight different spatial multiplex forms, to cater for the different HDTV formats used in different countries of the world, and for the prospect that a broadcaster may also receive 3DTV content in different forms.
The specification also allows for special treatment for subtitles for 3DTV services. It will be possible to include in the broadcast signal the depth location of blocks of subtitles. In this way, the subtitles can be positioned immediately in front of the particular character speaking. This will need a software upgrade of existing set-top boxes to be activated. But it is a great feature, and worth doing.
Another feature is an option of signaling to the set-top box to take one of the images of the spatial multiplex, stretch it out, and pass it to the display as a normal 2D picture. The specification explains that this is an option which may or may not be available, depending on the properties of the set-top boxes in a given market. This means it will probably be a ‘national option’ used where circumstances allow.
In the DVB project, attention has now shifted to a ‘Phase 2’ 3DTV system, for the world where it is not mandatory to use an existing set-top box. This is really exciting. Phase 1 does work very well, but now we look for additional features, provided they are commercially sound, to include in the Phase 2 specification.
One question is what picture quality it would be commercially viable to provide. At the moment most people believe it should be based on two ‘normal HDTV’ quality Left and Right images, without the limitation of sharing the HDTV bandwidth.
Another question is what ‘compatibility’ is required? What should still work when there is a Phase 2 broadcast? Should it be a 2D HDTV receiver (giving just one of the Left and Right images)? Should it be a set-top box and display that works with a Frame Compatible 3DTV broadcast? Possibly Phase 2 should actually do both.
One of the other features could be to build-in the capacity for the viewer to alter the ‘depth range’ of the 3DTV picture. On the remote control there would be a button to change the ‘3D-ness’ of the picture from flat 2D (good for older people?) to maximum depth range (good for younger people?).
The DVB group is also looking at other elements such as creating a 3DTV picture partially by broadcast and partially by internet download. Another issue is how sophisticated 3D multimedia should be.
Probably the number one issue however is ‘when should the Phase 2 system be ready’. The longer we wait, the better compression technology will become, and the more efficient the system will be. On the other hand, while we wait we are not serving the public – and (in relevant cases) not making any money. If you have a crystal ball please bring it along to our meetings.
David Wood is Chairman of the DVB-3DTV Commercial Module and the Deputy Director, Technology and Development at the European Broadcasting Union.
Copyright Tech-i 2011. Published with kind permission of EBU Technical.