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High definition television

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High Definition Television, or HDTV, is one of the formats used in digital television (DTV) broadcasting.

The HDTV screen uses a 16:9 aspect ratio. The high resolution images (1920 pixels × 1080 lines or 1280 pixels × 720 lines) allow much more detail to be shown. The images are expected to be at least 6 times as sharp as standard definition television or NTSC or PAL standard analog television. Like NTSC and PAL, most 1920x1080 broadcasts are to use interlacing to reduce bandwidth demands (giving the format the alternate name 1080i), a progressive-scan format is available, but reduces the number of frames per second to 24 (1080p24); 1280x720 will be broadcast in progressive-scan (with the entire frame refreshed each time) and is thus termed 720p. The refresh rate can be any of 24, 30 or 60 pictures per second.

It has been technically possible to create higher-resolution televisions for many years—for instance, computer monitors have been able to display high-resolution images with superior color and refresh rates since the 1980s. Japan began broadcasting analogue HDTV signals in the early 1990s using an interlaced resolution of 1035 lines (1035i)(more details anyone). Broadcasts of HDTV elsewhere are, as of 2002, only just beginning, and many countries show limited interest (most of Europe has instead gone to widescreen SDTV).

Because HDTV requires more broadcast spectrum, it has been the topic of great political controversy in the United States. According to FCC rules, all television broadcasting in the United States will by 2006 be conducted through HDTV, thereby rendering conventional televisions obsolete. The FCC ruled in August 2002 that all TV sets with screens of at least 36 inches must have digital tuners by July 2004, while the requirement for smaller sets would be phased in over the following three years.

Many have expressed doubts as to whether this will actually occur. TV monitors capable of showing HDTV pictures have started to appear on the marketplace, but they are quite expensive (upwards of 2000 USD as of 2002), and are only available in large screen sizes, where the extra resolution of HDTV makes the greatest difference. For more compact televisions, the benefits are considerably more marginal.

In an attempt to provide a bitrate-compatible high-definition format for high-definition DVDs, Microsoft introduced into their Windows Media 9 codec the ability to compress a high-definition bitstream into the same space as a conventional NTSC bitstream (approximately 5 to 9 megabits per second). It remains to be seen if the codec will be adopted for widespread use, if only as an ad hoc industry standard.

One of the reasons for the FCC's push for digital transmission is the desire to auction off the VHF band for a non-broadcast television use.


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