High-definition television


High-definition television 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. 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.
  • 1080p progressive scan: 2,073,600 pixels.
  • * Some countries also use a non-standard CTA resolution, such as : 777,600 pixels per field or 1,555,200 pixels per frame
When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD. 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. In the early 21st century, this race has continued with 4K, 5K and 8K systems.
The British high-definition television service started trials in August 1936 and a regular service debuted on 2 November 1936, using both the Baird 240 line sequential scan and the 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. All of these systems used interlacing and a 4:3 aspect ratio except the 240-line system which was progressive and the 405-line system which started as 5:4 and later changed to 4:3. The 405-line system adopted the 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.
The NHK began researching to "unlock the fundamental mechanism of video and sound interactions with the five human senses" in 1964, after the Tokyo Olympics. 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 aspect ratio and 60 Hz refresh rate. The Society of Motion Picture and Television Engineers, headed by Charles Ginsburg, became the testing and study authority for HDTV technology in the international theater. 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, and in 1979 an SMPTE study group released A Study of High Definition Television Systems:
  • 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
Since the formal adoption of Digital Video Broadcasting's widescreen HDTV transmission modes in the mid to late 2000s; the 525-line NTSC 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 lines system. 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, the first high-resolution 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.
In 1986, the European Community proposed HD-MAC, an analog HDTV system with 1,152 lines. A public demonstration took place for the 1992 Summer Olympics in Barcelona. However HD-MAC was scrapped in 1993 and the DVB project was formed, which would foresee development of a digital HDTV standard.

Japan

In 1979, the Japanese public broadcaster NHK first developed consumer high-definition television with a 5:3 display aspect ratio. The standard was known as Hi-Vision and used a system called MUSE for encoding the signal. It required about twice the bandwidth of the existing NTSC system but provided about four times the resolution. In 1981, the MUSE system was demonstrated for the first time in the United States, using the same 5:3 aspect ratio as the Japanese system. Upon visiting a demonstration of MUSE in Washington, US President Ronald Reagan was impressed and officially declared it "a matter of national interest" to introduce HDTV to the US. NHK taped the 1984 Summer Olympics with a Hi-Vision camera, weighing 40 kg.
Satellite test broadcasts started June 4, 1989, the first daily high-definition programs in the world, with regular testing starting on November 25, 1991, or "Hi-Vision Day"dated exactly to refer to its 1,125-lines resolution. Regular broadcasting of BS-9ch commenced on November 25, 1994, which featured commercial and NHK programming.
Several systems were proposed as the new standard for the US, including the Japanese MUSE system, but all were rejected by the Federal Communications Commission because of their higher bandwidth requirements. At this time, the number of television channels was growing rapidly and bandwidth was already a problem. A new standard had to be more efficient, needing less bandwidth for HDTV than the existing NTSC.

Decrease of analog HD systems

The limited standardization of analog HDTV in the 1990s did not lead to global HDTV adoption as technical and economic constraints at the time did not permit HDTV to use bandwidths greater than normal television. Early HDTV commercial experiments, such as NHK's MUSE, required over four times the bandwidth of a standard-definition broadcast. Despite efforts made to reduce analog HDTV to about twice the bandwidth of SDTV, these television formats were still distributable only by satellite. In Europe too, the HD-MAC standard was considered not technically viable.
In addition, recording and reproducing an HDTV signal was a significant technical challenge in the early years of HDTV. Japan remained the only country with successful public broadcasting of analog HDTV, with seven broadcasters sharing a single channel.
However, the Hi-Vision/MUSE system also faced commercial issues when it launched on November 25, 1991. Only 2,000 HDTV sets were sold by that day, rather than the enthusiastic 1.32 million estimation. Hi-Vision sets were very expensive, up to US$30,000 each, which contributed to its low consumer adaption. A Hi-Vision VCR from NEC released at Christmas time retailed for US$115,000. In addition, the United States saw Hi-Vision/MUSE as an outdated system and had already made it clear that it would develop an all-digital system. Experts thought the commercial Hi-Vision system in 1992 was already eclipsed by digital technology developed in the U.S. since 1990. This was an American victory against the Japanese in terms of technological dominance. By mid-1993 prices of receivers were still as high as 1.5 million yen.
On February 23, 1994, a top broadcasting administrator in Japan admitted failure of its analog-based HDTV system, saying the U.S. digital format would be more likely a worldwide standard. However this announcement drew angry protests from broadcasters and electronic companies who invested heavily into the analog system. As a result, he took back his statement the next day saying that the government will continue to promote Hi-Vision/MUSE. That year NHK started development of digital television in an attempt to catch back up to America and Europe. This resulted in the ISDB format. Japan started digital satellite and HDTV broadcasting in December 2000.