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High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). more...

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HDTV is digitally broadcast, because digital television (DTV) requires less bandwidth if sufficient video compression is used. HDTV technology was introduced in the U.S. in the 1990s by the Digital HDTV Grand Alliance, a group of television companies.

History of high-definition television

In 1949, France launched 819 lines television, first high definition public television network (778 active lines). This 819 lines network remained operational until 1983.

In 1958, the U.S.S.R. created Трансформатор (Transformer), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of televison conferences among military commands; as it was a military product, it was not commercialised.

In 1969, Nippon Hōsō Kyōkai (NHK) first developed commercial, high-definition television, yet, the system was not commercialised until late in the 1990s.

Currently, the International Telecommunication Union (ITU-R BT.709) defines three high-definition television systems: (i) the 1080i (1,080 actively-interlaced lines of resolution), (ii) the 1080p (1,080 progressively-scanned lines), and (iii) the 720p (720 progressively-scanned lines), each system produces a 16:9 aspect ratio image.

High-definition television refers to the image resolution and, loosely, to photo- and videographic media capable of such image resolution, i.e. photographic film and digital video. Current HDTV broadcast standards are in the ATSC and DVB specifications. HDTV is capable of cinema-quality audio, because it uses the Dolby Digital (AC-3) format to support the 5.1 surround sound system.

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. To get a better picture HDTV 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 an HD tuner is required. Most newer HDTV televisions have an 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 CableCARD 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) and Bell ExpressVu (in Canada), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.; Video game systems, such as the Xbox (NTSC only), Xbox 360, and Playstation 3, can output an HD signal. The Xbox Live Marketplace service offers HD movies, TV shows, movie trailers, and clips for download to Xbox 360 consoles.; Two optical disc standards, Blu-ray and HD DVD, can provide enough digital storage to store hours of HD video content.;

Read more at Wikipedia.org