The first Pay TV 3D-TV services will use what is called a ‘Frame Compatible’ approach. The Left and Right eye HD images are squeezed into a single HD TV channel. The 3D-TV picture can be viewed courtesy of a normal HDTV set top box, if the viewer has a (new) display that can separate out the Left and Right eye signals. There is a cost for squeezing the L and R signals into one channel, and this is some loss of image resolution for each of the L and R pictures. Some say that what we have now are two “HD minus” images.
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An alternative way to broadcast 3D-TV would be to use a ‘Service Compatible’ approach. Here the L and R signals are reproduced without loss of resolution, but this needs a much wider bandwidth than the Frame Compatible approach. The ‘Service Compatible’ approach, for example, that will be used for BluRay 3D (though not a broadcast system) needs nearly twice the bandwidth of a single HD signal. Will BluRay claim that it provides “Full HD 3D” and is better than the broadcast Frame Compatible picture? Probably, yes. |
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'Top up' system
At the HPA this week, there was a demonstration of a way to ‘upgrade’ a Frame Compatible 3D broadcast to “Full HD 3D”. They claim to have developed a new compression technology that can provide an enhancement signal to ‘top up’ the quality to full resolution. The enhancement signal takes very little space (less than 1 Mbit/s). This would offer an ‘upgrade path’ for those broadcasters who begin with Frame Compatible approach. How well does it work? Within the limits of a short demonstration, the answer is quite well. But, of course, a lot more discussion and testing needs to be done.
Contact 3D-TV expert David Wood (EBU), if you want to learn more.