High-definition television

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High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). HDTV is digitally broadcast, because digital television (DTV) requires less bandwidth if sufficient video compression is used. HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies.^[1][2]

[edit] History of high-definition television

Main article: Analog high-definition television systems

The term high definition described the television systems of the 1930s and 1940s beginning with the British 405-line black-and-white system, introduced in 1936; however, it and the American 525-line NTSC system established in 1941, were high definition in comparison with previous mechanical and electronic television systems. Today, the American 525-line NTSC system and the European 625-line PAL and SECAM systems are standard definition television, whereas the post–WWII French 819-line black-and-white system, was high definition in the contemporary sense, it required more bandwidth and was discontinued in 1986, a year after the final British 405-line broadcast.

In 1949, France launched the first high definition public television network with 819-line (778 active-line) resolution. This network remained operational until 1983.^{[citation needed]}

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 television conferences among military commands; as it was a military product, it was not commercialised.^[3]

In 1969, NHK of Japan first developed commercial, high-definition television.^[4] However, the system was not commercialized until late in the 1990s.

In 1983, the International Telecommunication Union's radiotelecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. This WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas such as conversion between 30/60 and 25/50 picture rates using motion vectors that led to other outcomes. While a single standard was never finalized, a common aspect ratio of 16:9 was agreed to at the first meeting at the BBC's R & D establishment at Kingswood Warren. Initially the Japanese 5:3 ratio was considered but a proposal to widen it to 5 1/3:3 = 16:9 was accepted. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, specified colorimetry, and 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines) scanning modes. It also includes the 1440 x 1152 HDMAC scanning format. 720p formats were strongly resisted by some ITU-R members^{[citation needed]} and were not standardized there. Both 1920x1080 and 1280x720p (720 progressively-scanned lines) systems for a range of frame and field rates are also defined by several SMPTE standards.

However, the standardization of HDTV did not lead to its adoption. Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard definition broadcast, and despite the effort made to shrink the required bandwidth into about 2 times of that of the SDTV's, it still was distributable only by satellite. In addition, recording and reproducing an HDTV signal was also a technical challenge in the early years of HDTV. Nevertheless, the first HDTV sets went on sale in the United States in 1998.

Japan is the only country with successful commercial analog HDTV, known as "Hi-vision", featuring a 5:3 aspect ratio screen with 1,125 interlaced lines (1,035 active lines) at the rate of 60 fields per second. Elsewhere, in Europe, analog 1,125-line HD-MAC television failed in its test broadcasts in the early 1990s.

However, it was not until the early 2000's that storage means of enough capacity and computer processing power for dense compression algorithms made commercial applications of HDTV affordable for consumers and profitable for TV channels or the video rental industry.

HDTV became viable due to the transition from analog to digital TV broadcasting. Digital compression methods such as MPEG-2 and MPEG-4 allow the bandwidth of a single TV channel (in the US, 6 MHz) to carry up to 5 TV programs of standard definition or up to 2 channels of high definition.

Current HDTV broadcast standards include ATSC (US) and DVB (Europe). HDTV can also provide 5.1-channel surround sound audio using e.g. the Dolby Digital (AC-3) format.

On February 17, 2009, the US will terminate all terrestrial analog broadcasting in favor of digital broadcasting, which can be standard-definition (SDTV) or HDTV.^[5]

[edit] 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 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 an HD tuner is required. Most newer high definition 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), Bell ExpressVu (in Canada) and NTV Plus (in Russia), 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, Playstation 2 (Gran Turismo 4) and Playstation 3 can output an HD signal. The Xbox Live Marketplace and Playstation Network services offers HD movies, TV shows, movie trailers, and clips for download to their respective consoles.
• Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.
• Two optical disc standards, Blu-ray Disc and HD DVD, can provide enough digital storage to store hours of HD video content.DVDs look best on screens that are smaller than 36 inches, so they're not always up to the challenge of today's high-definition (HD) sets. To store and play HD movies, you need a disc that holds more information, like an HD-DVD. A DVD holds about two hours of standard definition video, but an HD-DVD can hold about 48 hours.^[6]

[edit] Notation

HDTV broadcast systems are defined threefold, by:

• The number of lines in the vertical display resolution.

• The scanning system: progressive scanning (p) or interlaced scanning (i). Progressive scanning redraws an image frame (all of its lines) when refreshing each image. Interlaced scanning redraws the image field (every second line) per each image refresh operation, and then redraws the remaining lines during a second refreshing. Interlaced scanning yields greater image resolution if subject is not moving, but loses up to half of the resolution and suffers "combing" artifacts when subject is moving.

• The number of frames per second or fields per second.

The 720p60 format is 1280 × 720 pixels, progressive encoding with 60 frames per second (60 Hz). The 1080i50 format is 1920 × 1080 pixels, interlaced encoding with 50 fields per second. Sometimes interlaced fields are called half-frames, but they are not, because two fields of one frame are temporally shifted. Frame pulldown and segmented frames are special techniques that allow transmitting full frames by means of interlaced video stream.

For commercial naming of the product, either the frame rate or the field rate is dropped, e.g. a "1080i television set" label indicates only the image resolution.^[7] Often, the rate is inferred from the context, usually assumed to be either 50 or 60, except for 1080p, which denotes 1080p24, 1080p25, and 1080p30, but also 1080p50 and 1080p60 in the future.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second. Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.

[edit] Standard Display Resolutions

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution of 720 or 704 "pixels".