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High-definition

A general term for a video signal with a significantly higher resolution than standard definition.

High-definition video (HD video) is a video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with considerably more than 480 vertical lines (North America) or 576 vertical lines (Europe) is considered high-definition. Four hundred and eighty scan lines are generally the minimum even though the majority of systems greatly exceed that. Images of standard resolution captured at rates faster than normal (60 frames/second North America, 50 fps Europe), by a high-speed camera may be considered high-definition in some contexts. Some television series shot on high-definition video are made to look as if they have been shot on film, a technique which is often known as filmizing.

The first electronic scanning format, 405 lines, was the first "high definition" television system since the mechanical systems it replaced had far fewer. From 1939, Europe and the US tried 605 and 441 lines until, in 1941, the FCC mandated 525 for the US. In wartime France, René Barthélemy tested higher resolutions, up to 1,042. In late 1949, official French transmissions finally began with 819. In 1984, however, this standard was abandoned for a 625-line color on the TF1 network.

Analog

Modern HD specifications date to the early 1980s when Japanese engineers developed the HighVision 1,125-line interlaced TV standard (also called MUSE) that ran at 60 frames per second. The Sony HDVS system was presented at an international meeting of television engineers in Algiers, April 1981 and Japan's NHK presented it's analog high-definition television (HDTV) system at a Swiss conference in 1983.

The NHK system was standardized in the United States as Society of Motion Picture and Television Engineers (SMPTE) standard #240M in the early 1990s but abandoned later on when it was replaced by a DVB analog standard. HighVision video is still usable for HDTV video interchange, but there is almost no modern equipment available to perform this function. Attempts at implementing HighVision as a 6 MHz broadcast channel were mostly unsuccessful. All attempts at using this format for terrestrial TV transmission were abandoned by the mid-1990s.

Europe developed HD-MAC (1,250 lines, 50 Hz), a member of the MAC family of hybrid analog/digital video standards; however, it never took off as a terrestrial video transmission format. HD-MAC was never designated for video interchange except by the European Broadcasting Union.

Digital

High-definition digital video was not possible with uncompressed video due to impractically high memory and bandwidth requirements, with a bit-rate exceeding 1 Gbps for full HD video. Digital HDTV was enabled by the development of a discrete cosine transform (DCT) video compression. The DCT is a lossy compression technique that was first proposed by Nasir Ahmed in 1972 and was later adapted into a motion-compensated DCT algorithm for video coding standards such as the H.26x formats from 1988 onwards and the MPEG formats from 1993 onwards. Motion-compensated DCT compression significantly reduced the amount of memory and bandwidth required for digital video, capable of achieving a data compression ratio of around 100:1 compared to uncompressed video. By the early 1990s, DCT video compression had been widely adopted as the video coding standard for HDTV.

The current high-definition video standards in North America were developed during the advanced television process initiated by the Federal Communications Commission in 1987 at the request of American broadcasters. In essence, the end of the 1980s was a death knell for most analog high definition technologies that had developed up to that time.

The FCC process, led by the Advanced Television Systems Committee (ATSC) adopted a range of standards from interlaced 1,080-line video (a technical descendant of the original analog NHK 1125/30 Hz system) with a maximum frame rate of 30 Hz, (60 fields per second) and 720-line video, progressively scanned, with a maximum frame rate of 60 Hz. In the end, however, the DVB standard of resolutions (1080, 720, 480) and respective frame rates (24, 25, 30) were adopted in conjunction with the Europeans that were also involved in the same standardization process. The FCC officially adopted the ATSC transmission standard (which included both HD and SD video standards) in 1996, with the first broadcasts on October 28, 1998.

In the early 2000s, it looked as if DVB would be the video standard far into the future. However, both Brazil and China have adopted alternative standards for a high-definition video that preclude the interoperability that was hoped for after decades of largely non-interoperable analog TV broadcasting.

Key Terms

europe
fcc
high definition
high definition video
hz
lines
north america
us
vertical lines
video

Additional Resources

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Acronymn

HD

Synonymns

High-definition
(none found)

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Sources & Credits

Last modified on November 3 2019
Content adapted from Wikipedia
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