Tuesday, March 25, 2008

High-Definition Television

High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC -National Television System Committee, SECAM-Sequential Couleur Avec Memoire or Sequential Color with Memory, PAL-Phase Alternating Line). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. A HDTV compatible television set will not improve the quality of SDTV channels. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal a HD tuner is required. Most new high definition televisions have a HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.

Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or Cable CARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.

Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu and Star Choice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade.

Video game systems, such as the Xbox, PlayStation 3, and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output a HD signal. The Xbox Live Marketplace, iTunes, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but at lower bit rates than Blu-ray or HD-DVD.

Most new computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to a HDTV.

Two optical disc standards, Blu-ray Disc (25GB-50GB) and HD DVD (15GB-30GB), can provide enough digital storage to store hours of HD video content.

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