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High Definition Television

Photograph of Philips HDTV plasma TVAs larger television screens have become available along with the introduction of liquid crystal and plasma displays, it has been found that on screens with a diagonal of above 37-40 inches, standard definition television pictures with 576 vertical lines show up various forms of undesirable artefacts, and that more detail (i.e. higher resolution), which can be provided by High Definition TV, which has 720 or 1080 lines as well as more picture elements along each TV line, provides more acceptable pictures. The highest resolution you can appreciate depends on the size of the screen and how close you view it from, as well as on how good your eyesight is.

Research by the BBC showed that the average TV viewing distance in the home is currently between six and eight times the picture height, which turned out to be an average distance of around 2.7 metres. As screen sizes increase, since it will not generally be possible to move the chairs further away from the screen, the effective viewing distance will become closer in terms of screen height, and one of the assumptions for HDTV has been that the pictures will need to be excellent when viewed from the much closer distance of 3H – three times the height of the screen.

Diagram showing viewing distances

One rough estimate is that at such a distance those with 20/20 vision will be content with standard definition 576 lines up to screen diagonal sizes of 37", 720 lines up to 45" and 1080 lines up to 70". People with poorer eyesight, perhaps 20/30 or 20/40 vision, may not benefit from HDTV at all, whereas those with better than average vision, 20/15 or 20/10 will be able to appreciate the benefits of HDTV on smaller screens.

Photograph from Philips showing clarity of HDTVHDTV gives very clear, crisp pictures with vivid colours and much more detail than ordinary standard-definition TV, and some programmes are made with cinema-style "surround sound". At the present time in the UK, HDTV transmissions are available only from satellite and cable platforms, since there is insufficient bandwidth available to carry HD services on DTT – digital terrestrial television. In the longer term, towards the end of the digital switchover period, it may become possible to broadcast a limited number of HD channels on DTT using newer technologies, which will include the adoption of a new coding standard, called MPEG4, which is expected to be up to twice as efficient as the current MPEG2 standard, and the use of a new European transmission standard, called DVB-T2, which will increase transmission capacity by over 40 per cent..

To watch HD programmes, you need an HD-ready TV set and a special set-top box which is designed for HD. You also need a satellite dish or cable connection. Sky TV currently offers, as part of a subscription service, some six HD programme channels, including movies, sports, and arts programmes, plus other HD programmes ‘on demand’, via the Sky HD box, which also contains a hard drive for storing and pausing programmes.

BBC HD is currently broadcasting several hours a day of HD material via an Astra satellite (and also supplies the HD programmes to the Virgin Media cable companies for transmission in HD). This service is free, and once the freesat satellite service is launched there will be an increased amount of HD broadcasting from both BBC and the Independent Television companies, again on a free to air basis. The only cost will be the initial cost of the box and its installation.

The Virgin Media cable service offers a range of broadcast and ‘on-demand’ HD services via its V+ box, which contains a hard-disk which offers easy recording and programme pause facilities. There are various charging schemes.

Buying HDTV equipment

TV technology is changing fast, and it is important to take advice before making the sizeable investment that HD involves. When buying a TV set, make sure it is marked "HD ready", but note that this only specifies a minimum standard for HD, and there are other decisions to be made, some of which can affect how ‘future proof’ the equipment may turn out to be, including whether you want to go for a 720 line progressive display, 1080 line interlaced, or 1080 line progressive (sometimes called Full HD) – each has its pros and cons. Note that some form of box is required to receive any of the current or planned HDTV services – if you buy a current integrated Digital TV (i.e. a TV with a built-in digital tuner) this will provide only standard definition services, even though it may be marked ‘HD Ready’.

Photograph of High Definition Multimedia Interface (HDMI) connectorsThe HD Ready TV will be connected to the HD set top box with an HDMI (High Definition Multimedia Interface) connector and lead. The same type of lead will be used for connecting new high definition DVD players such as Blu-Ray to the TV, and also for some games consoles, which can provide the highest quality 1080 line progressive outputs, so it is useful to ensure that the TV has more than one HDMI connector.

To experience the ‘surround sound’ that accompanies some HD broadcasts it is necessary to install a multiple speaker surround sound amplifier system and connect this to your TV.

Programmes have to be specially made in HD, and then broadcast in HD too. An HD-ready TV set won't turn a standard-definition programme into an HD one, and it won't display HD unless you feed it from an HD source.

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