Projection screen in a home theater, displaying a high-definition television image.
High-definition television (HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.
History of high-definition television
The term high definition once described a series of television systems from the 1930s and 1940s, starting with the British 240 line and 405 line black-and-white systems introduced in 1936, and including the American 525-line NTSC system established in 1941. However, these systems were only "high definition" when compared to earlier systems.
The British high definition TV service started trials in August 1936 and a regular service in November 1936 using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937.
A brief itemized history of early analog HD systems follows; these would be considered standard definition television systems today.
All used interlacing and a 4:3 aspect ratio except the 405 line system which started as 5:4 and later changed to 4:3.
The post–WWII French 819-line black-and-white system was high definition in the contemporary sense, but was discontinued in 1986, a year after the final British 405-line broadcast. Experimental 405 line colour transmissions were made in the 1950s using a modified NTSC system.
Since the formal adoption of DVB's widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as standard definition television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.[1]
Color
In Mexico, Guillermo González Camarena (1917–1965), invented an early color television transmission system. He received patents for colour television systems in 1942 (U.S. Patent 2,296,019), 1960 and 1962. The 1942 patent (filed in Mexico on August 19, 1940) was for a synchronized colour filter wheel adapter for monochrome television, similar to the field sequential colour receiver demonstrated by Baird in England in July 1939[53] and by CBS in the United States in August 1940. __
On August 31, 1946 González Camarena sent his first colour transmission from his lab in the offices of The Mexican League of Radio Experiments at Lucerna St. #1, in Mexico City. The video signal was transmitted at a frequency of 115 MHz. and the audio in the 40 meter band. He made the first publicly announced colour broadcast in Mexico, on February 8, 1963, of the programme Paraíso Infantil on Mexico City's XHGC-TV.
In 1958, the U.S.S.R. created Тransformator (Russian: 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 commercialized.
Modern systems
In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard.[3] However, the system was not launched publicly until late in the 1990s.
In 1981, the first HDTV demonstration in the United States was held. It had the same 5:3 aspect ratio as the Japanese system.[4] Upon visiting a demonstration of the Japanese Multiple sub-nyquist sampling Encoding system (MUSE) HDTV system in Washington, US President Ronald Reagan was most impressed and officially declared it "a matter of national interest" to introduce HDTV to the USA. Several systems were proposed as the new standard for the USA, including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirement.
A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV. It was commonly understood only a digital system could possibly bring desired results, however nothing such had yet been developed. Pattern-recognition research for cruise missile development at the NASA Jet Propulsion Laboratory provided the basis for developing the MPEG set of compression standards.
The rise of digital compression
As soon as the MPEG-1 standard provided the foundation for digital TV, development of modern TV standards started worldwide. After finalization of MPEG-2 in mid 1993, the DVB organisation within the International Telecommunication Union's radio telecommunications sector (ITU-R) developed the ETSI standard 300-327 by the end of December 1993.
It became known as DVB-T for digital terrestrial TV. DVB-S and DVB-C standards soon followed for terrestrial, satellite and cable transmission of SDTV and HDTV. In the USA the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.
In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their mains electrical supplies.
The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.
Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has been suggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy Ratio, and 2.35:1, the widest cinema format in common use, in order to minimise wasted screen space when displaying content with a variety of aspect ratios.)
An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC's R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines).
It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an "enhanced" television format rather than a true HDTV format,[5] and so was not included, although 1920x1080 and 1280x720p systems for a range of frame and field rates were defined by several US SMPTE standards.)
The demise of analog HD systems
However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard-definition (SDTV) broadcast, and despite efforts made to shrink the required bandwidth down to about 2 times that of SDTV, it was still only distributable by satellite. In addition, recording and reproducing a HDTV signal was a significant technical challenge in the early years of HDTV. Japan remained the only country with successful public broadcast 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. The single satellite transponder MUSE service was turned off on January 1, 2007.
In Europe, analog 1,125-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.
Inaugural Digital HDTV Public broadcast
HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies and MIT.[6][7] On April 6, 1997, CBS went on the air with WCBS-HD from the top of the Empire State Building, New York, doing demos and evaluations.[8] Astronaut John Glenn's return to space, on board the Space Shuttle Discovery wasn't the only thing launched on October 29, 1998. The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch during the live coverage of the lift-off.[9] The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.[9] The broadcast was made possible by the Harris Corporation, which sponsored the equipment necessary for transmitting and receiving the broadcast.[9] The broadcast was hosted by former CBS News anchor, Walter Cronkite, former Gemini/Apollo era astronaut Pete Conrad and former NBC News anchor Mary Alice Williams.[10]
Modern digital compression and standardization
Digital compression methods such as MPEG-2 and H.264/MPEG-4 AVC allow the bandwidth of a single analog TV channel (6 MHz in the US) to carry up to 5 standard-definition or up to 2 high-definition digital TV channels instead.
Most developed nations have plans in place for a transition to digital television, but not necessarily (or exclusively) to HDTV.
For example, on February 17, 2009, the US will terminate all full-power terrestrial analog broadcasting (although some smaller local stations have later deadlines), with both standard definition TV (SDTV) and HDTV being allowed.
Current HDTV broadcast standards include ATSC (North America, parts of Central America and South Korea), DVB (Europe, Australia, parts of Asia, South America and Africa) and ISDB-T (Japan, Brazil).
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. It will make it even worse because of scaling artifacts. 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 Astra (in the Netherlands), Premiere (in Germany), DirecTV and Dish Network (both in North America), Sky Digital and freesat (in the UK and Ireland), Bell TV and Star Choice (both 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 PlayStation 3 and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output an HD signal. The Xbox Live Marketplace, iTunes Music Store, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but generally at lower bitrates than a Blu-ray Disc.
Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.
The optical disc standard Blu-ray Disc (25GB-50GB) can provide enough digital storage to store up to 10 hours of HD video content, depending on encoder settings.[12]
A DVD-R disc (~4.7GB-9GB) can also provide storage for up to 3 hours of HD video content, readable by a Blu-ray player, PlayStation 3 video game console or Blu-ray drives installed on PC towers, depending on encoder settings.
Notation
HDTV broadcast systems are identified with three major parameters:
Frame size in pixels is defined as number of horizontal pixels x number of vertical pixels, for example 1280 x 720 or 1920 x 1080. Often number of horizontal pixels is implied from context and is omitted.
Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.
Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used. Recently the uniform notation of specifying number of frames per second both for progressive and interlaced video became increasingly popular.[14]
If all three parameters are used, they are specified in form frame size scanning system frame rate. Often, one parameter can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.
For example, 1920x1080p25 identifies progressive scanning format with 25 frames per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i25 or 1080i50 notation identifies interlaced scanning format with 50 fields(25 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i30 or 1080i60 notation identifies interlaced scanning format with 60 fields (30 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 720p60 notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high, 1280 pixels horizontally are implied.
While 50Hz systems have only three scanning rates: 25i, 25p and 50p, 60Hz systems operate with much wider set of frame rates: 23.98p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, like 23.98p was often called 24p, or 59.94i was often called 60i. High definition television allows using both fractional and whole rates, therefore strict usage of notation is required. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.98p is called 24p.
For commercial naming of a product, the frame rate is often dropped and is implied from context, e.g. a "1080i television set". A frame 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. Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.
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