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october 2010
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3D Television
3D is no longer just a 1950s fad. Leaps in HD TV technology mean that 3D viewing has progressed a long way from the cardboard glasses of yesteryear The start of consumer 3D TV in the UK is another milestone in the development of our home entertainment. For 3D viewing, TV has got a bit more complicated.
The illusion of depth is given by displaying two separate images at once, one for each eye
What is 3D TV?
01 3D TV imitates the way we perceive solid objects and scenes with depth by presenting each of our eyes with a different (moving) image. Two images are captured for each TV frame, with cameras spaced apart like our own eyes, then these images are displayed so each of your eyes sees only the appropriate left or right image, and together these make up a stereoscopic 3D image, as though actually observing the recorded scene. 3D TV provides only an illusion of depth with a fixed point of view – you cannot ‘look around’ an object – but it increases realism and involvement in your viewing. What’s new about 3D?
02 3D images have been around for many years, in photography, cinema and TV. So-called ‘anaglyphic’ films of the 1960/1970s coloured the left and right images differently and projected both onto the screen at once. The audience wore glasses with coloured lenses (red and cyan) to separate the image for each eye. Anaglyphic 3D TV programmes have been broadcast in the past but image quality (especially colour) is poor. More recently, 3D films have projected two concurrent images of different polarisations and the audience uses glasses with oppositely polarised lenses so each eye sees only the correct image. This produces better colour fidelity and less ghosting than anaglyphic 3D. The 3D TV technology arriving in homes today also employs polarisation but it is ‘frame sequential’ – the left and right images are displayed one after another in very quick succession. Special 3D glasses direct each image in turn to the correct eye. Successful 3D TV using this technique has only been practical with the widespread availability and use of digital HD TV sets. What are the special 3D TV
03 glasses?
2 What Satellite & Digital TV October 2010
Capture
Signal processing
Broadcast
Reception
Display
Viewing
The 3D glasses are probably the biggest stumbling block for universal enthusiasm for 3D TV. Two systems for displaying and separating the left and right images are currently available. One system uses a special TV screen (or projector) to polarise the left and right images differently, and simple, cheap ‘passive’ polarising glasses (like the cinema ones) to separate the images.
An alternative, and more common, system displays both the left and right images in turn on a normal screen but uses expensive battery-operated ‘active’ LCD glasses, which blank and clear the lenses alternately, synchronised (usually by an infrared signal) with the TV display, to allow each eye to see only the image intended for it. With the Passive system, the expense is
abc guide to... in the TV and the glasses should cost from about 50p to a few pounds each. What’s more, they are light and robust. An Active system TV is almost unchanged from a ‘normal’ HD TV but the glasses are heavier, fragile (would you trust your kids with them?), require (battery) power, and can cost £100 a pair. Obviously, the more viewers you have (or will have), the better the passive system is financially. Performance-wise, the general consensus is that Active glasses have the edge, but it’s a close call. Glasses for both systems will fit over most existing prescription glasses. Where can I get 3D content?
04 3D TV content is available now from Blu-ray 3D discs (on a Blu-ray 3D player), from games consoles, and from satellite (Sky 3D). In the coming months, Virgin Media aims to provide on-demand 3D TV by cable and, looking further ahead, digital terrestrial TV may one day carry 3D content too, maybe using a slightly different 3D delivery format. For the moment, 3D TV is the realm of pay-TV providers and, with the exception of demo channels, watching TV 3D, requires a subscription to pay-TV, even if you don’t have to pay extra for a particular 3D channel itself. It’s likely, however, that should 3D TV continue to catch on, 3D TV sales rise and production costs fall, in the future free-to-air and public broadcasters will also begin to show 3D content. Do I need a new TV for 3D?
05 To watch any kind of 3D
programming you will need a 3D-Ready TV and the corresponding type of 3D glasses. All 3D TVs are also (2D) HD TVs, and some more recent HD sets can be retrofitted with extra equipment to enable them to display 3D images and drive 3D glasses. The 3D glasses required to see the 3D effect are expensive, so if you want to ‘go 3D’ you should think about buying any extra glasses you will need in a package along with the TV as it may be cheaper. Be aware that there is no standard for 3D glasses, so you will need to buy the ones from your own TV’s manufacturer. Also note that a few TVs advertised as ‘3D-Ready’ have the required fast refresh rate and HDMI 1.4 input but no 3D image processing or 3D glasses synchronisation, and can’t actually be used for 3D viewing. Do I need a new set-top box for
06 3D?
Although Blu-ray 3D requires a special Blu-ray 3D player to watch 3D content, 3D broadcast by satellite (and cable) requires a standard HD receiver, such as the Sky+
HD box (or Virgin V+ box). This is because the 3D programmes are broadcast in a ‘side by side’ format – with the left and right images compressed horizontally to fit in one normal-sized frame. The 3D-Ready TV separates the images and displays them sequentially to give the 3D effect. Although this means that if you have Sky HD you won’t need a new box, it also means that 3D programming is not broadcast or viewed in full HD resolutions. Can I watch 2D on a 3D TV, or 3D
07 on a 2D TV?
You will not be able to watch satellite, cable, DTT or Blu-ray 3D programmes on a normal 2D screen. You can watch a 3D Blu-ray disc (in 2D) played on a normal 2D player but 3D broadcasts will not be shown at all on a 2D TV set. However, if you have a 3D-Ready TV, this can be used to watch 2D programmes (including HD material) as well as 3D – and you don’t need to wear
‘Active’ 3D TV glasses separate the left and right images by blocking the wrong one from each eye as they are displayed in turn
the 3D glasses when watching 2D shows. Some 3D TV sets also provide a pseudo-3D facility to make 2D programming look more 3D (when viewed in 3D mode with 3D glasses) but this is a far cry from proper 3D. Is 3D TV safe?
08 There are some signs that prolonged use of 3D glasses can produce eye fatigue, headaches, dizziness or disorientation, or even nausea in some viewers. It seems these problems are largely restricted to early 3D TVs that flashed up the alternate left and right images at a slower rate than more recent sets, and some studies put ill effects down to the programming and not the equipment. While it’s probably not necessary to take off 3D glasses for while after an hour (as has been suggested) it would be wise to resurrect the common advice of 40 years ago, and not to sit watching (3D) TV too close or for too long n Geoff Bains October 2010 What Satellite & Digital TV 3