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.
Twice the bandwidth
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.
'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.