High-definition television (HDTV; also known as high-definition or HD) describes a television or video system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since at least 1933; in more recent times, it refers to the generation following standard-definition television (SDTV). It is the standard video format used in most broadcasts: terrestrial broadcast television, cable television, and satellite television.
Formats HDTV may be transmitted in various formats: 720p (): 921,600 pixels 1080i () interlaced scan: 1,036,800 pixels (≈1.04Mpx). 1080p () progressive scan: 2,073,600 pixels (≈2.07Mpx). Some countries also use a non-standard CTA resolution, such as : 777,600 pixels (≈0.78Mpx) per field or 1,555,200 pixels (≈1.56Mpx) per frame
When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD (standard-definition television). The increased resolution provides for a clearer, more detailed picture. In addition, progressive scan and higher frame rates result in a picture with less flicker and better rendering of fast motion. Modern HDTV began broadcasting in 1989 in Japan, under the MUSE/Hi-Vision analog system. HDTV was widely adopted worldwide in the late 2000s.
Standards
All modern high-definition broadcasts utilize digital television standards.
The major digital television broadcast standards used for terrestrial, cable, satellite, and mobile devices are: DVB, originating in Europe and also used in much of Asia, Africa, and Australia ATSC, used in much of North America DTMB, used in China and some neighboring countries ISDB, used in two incompatible variations in Japan and South America DMB, used by mobile devices in South Korea
These standards use a variety of video codecs, some of which are also used for internet video.
History
The term high definition once described a series of television systems first announced in 1933 and launched starting in August 1936; however, these systems were only high definition when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution. The ongoing competition between companies and nations to create true HDTV spanned the entire 20th century, as each new system became higher definition than the last. With the 525-line NTSC and 625-line PAL and SECAM analog TV standards used in most countries through the 1980s, the term High Definition Television became used for future broadcast systems with much higher resolution, typically at least 4-5X the resolution of these NTSC, PAL, and SECAM standards. Digital HDTV signals with 720p (Progressive) and 1080i (Interlaced) resolutions started to be delivered in the late 1990s and early 2000s, followed by 1080p. In the 2014-16 timeframe, this race continued with 4K, and later 5K (with some computer monitors), and 8K systems.
The British television service started trials in August 1936, and a regular service debuted on 2 November 1936, using both the (mechanical) Baird 240 line sequential scan (later referred to as progressive) and the (electronic) Marconi-EMI 405 line interlaced systems. The Baird system was discontinued in February 1937. In 1938, France followed with its own 441-line system, variants of which were also used by a number of other countries. The US NTSC 525-line system joined in 1941. In 1949, France introduced an even higher-resolution standard at 819 lines, a system that would have been high definition even by modern standards, if it had not required such bandwidth for a color version, which prevented the addition of other TV channels (nevertheless, it remained in use until 1983). All of these systems used interlacing and a 4:3 aspect ratio except the 240-line system which was progressive (actually described at the time by the technically correct term sequential) and the 405-line system which started as 5:4 and later changed to 4:3. The 405-line system adopted the (at that time) revolutionary idea of interlaced scanning to overcome the flicker problem of the 240-line with its 25 Hz frame rate. The 240-line system could have doubled its frame rate but this would have meant that the transmitted signal would have doubled in bandwidth, an unacceptable option as the video baseband bandwidth was required to be not more than 3 MHz.
Color broadcasts started at similar line counts, first with the US NTSC color system in 1953, which was compatible with the earlier monochrome systems and therefore had the same 525 lines per frame. European standards did not follow until the 1960s, when the PAL and SECAM color systems were added to the monochrome 625-line broadcasts.
In the late 1980s, both Japan (NHK) and Europe (the EU and various companies such as Philips and Thomson) were developing analog HDTV systems, called MUSE and HD-MAC respectively. Then, General Instrument Corporation's VideoCipher Division, based in San Diego, California, announced the development of an all-digital HDTV system, marking the possibility that HDTV signals could be efficiently broadcast over satellite, cable, and over-the-air spectrum. General Instrument demonstrated the feasibility of an all-digital HDTV signal, persuading the FCC to delay its decision on an advanced television (ATV) standard for the US until a digitally-based standard could be developed, resulting in several actions. First, the FCC declared that the new TV standard must be more than an enhanced analog signal, capable of providing a genuine HDTV signal with at least twice the resolution of existing television images. Second, to ensure that viewers who did not wish to buy a new digital television set could continue to receive conventional television broadcasts, it dictated that the new ATV standard must be capable of being simulcast with NTSC on different channels. The new ATV standard also allowed the new DTV signal to be based on entirely new design principles, incorporating many improvements over existing analog television.
General Instrument (GI), however, recognized that digital HDTV would likely take many years for market development, therefore deciding to focus its original product development and marketing plans on a digital standard definition system (digital SDTV) for satellite TV and cable TV applications, receivable via a home digital set-top box for display on the enormous global installed base of NTSC, PAL, and SECAM television sets.
Because there were no technical standards yet for digital TV, GI had to develop a complete (proprietary) end-to-end digital TV system comprising: (a) its breakthrough video compression algorithms; (b) a new digital transmission system (forward error correction coding and digital modulation for satellite and cable delivery); and (c) a conditional access and encryption system for content security and monetization by media companies.
At the September 1990 International Broadcasting Convention (IBC) trade show in Brighton, England, GI demonstrated its DigiCipher digital television system, incorporating a flexible degree of compression from 2:1 (HD) and up to 10:1 (SD) within a single satellite transponder or 6 MHz cable TV channel, effectively giving a 10X bandwidth efficiency improvement relative to analog TV. The advent of digital SDTV television meant, in the US and elsewhere, that Direct Broadcast Satellite (DBS) services could suddenly deliver hundreds of digital TV channels through a single high-power satellite to pizza-size home dishes, thereby becoming the first real competitive threat to the dominant cable operators.
Meanwhile, the US over-the-air broadcast HDTV process was undergoing a rigorous process conducted by the FCC's Advisory Committee on Advanced Television Service (ACATS) through its Advanced Television Test Center (ATTC) located in Alexandria, Virginia. After GI announced digital HDTV, six HDTV systems were tested sequentially in 1992. The digital HDTV prototypes were developed by: General Instrument, in partnership with MIT; a competing consortium comprising Philips, Thomson, Sarnoff Labs, and NBC; and another alliance of Zenith Electronics and AT&T. After the competitive testing phase, the various companies were strongly encouraged to come together in a "Grand Alliance," with a goal of combining the various technologies into a unified digital HDTV broadcast system. Key technical elements of the system included MPEG-2 video (with interlaced and progressive formats), Dolby AC-3 audio, MPEG-2 transport, System Information (SI) tables, and 8-VSB transmission.
Since the formal adoption of Digital Video Broadcasting's (DVB) widescreen HDTV transmission modes in the mid to late 2000s, the 525-line NTSC (and PAL-M) systems, as well as the European 625-line PAL and SECAM systems, have been regarded as standard definition television systems.
Analog systems
Early HDTV broadcasting used analog technology that was later converted to digital television with video compression.
In 1949, France started its transmissions with an 819-line system (with 737 active lines). The system was monochrome only and was used only on VHF for the first French TV channel. It was discontinued in 1983.
In 1958, the Soviet Union developed Transformator (, meaning Transformer), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution aimed at providing teleconferencing for military command. It was a research project and the system was never deployed by either the military or consumer broadcasting.
Development The NHK (Japan Broadcasting Corporation) began researching to "unlock the fundamental mechanism of video and sound interactions with the five human senses" in 1964, after the Tokyo Olympics. In 1970 they began developing HDTV with extensive pyschophysical testing and in 1972 submitted a draft of their study program to Study Group II of Comité Consultatif International Radio (CCIR). NHK set out to create an HDTV system that scored much higher in subjective tests than NTSC's previously dubbed HDTV. This new system, NHK Color, created in 1972, included 1125 lines, a 5:3 (1.67:1) aspect ratio and 60 Hz refresh rate. In 1973, NHK published papers on a 1125 line camera and CRT display devices, and the following year, the CCIR Study Group II issued Report 801 on HDTV.
In 1977, the Society of Motion Picture and Television Engineers (SMPTE), headed by Charles Ginsburg, formed a study group on HDTV and became the testing and study authority for HDTV technology internationally. SMPTE would test HDTV systems from different companies from every conceivable perspective, but the problem of combining the different formats plagued the technology for many years.
There were four major HDTV systems tested by SMPTE in the late 1970s: EIA monochrome: 4:3 aspect ratio, 1023 lines, 60 Hz NHK color: 5:3 aspect ratio, 1125 lines, 60 Hz NHK monochrome: 4:3 aspect ratio, 2125 lines, 50 Hz BBC colour: 8:3 aspect ratio, 1501 lines, 60 Hz
The output of the SMPTE study group was released in 1980.
In 1978, A Study of High Definition Television Systems in the Future by Dr Takashi Fujio of NHK was published in the Institute of Electrical and Electronics Engineers' Transactions on Broadcasting. The same year, the first satellite transmission tests of 1125 line HDTV signals were performed in Japan (although not reported on until 1980) and the BBC published a report raising the possibility of broadcasting by satellite and the potential impact on HDTV standards.