Analog high-definition television system
From Wikipedia, the free encyclopedia
Historically, the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines. Not so long afterwards,John Logie Baird, Philo T. Farnsworth and Vladimir Zworykin had each developed competing TV systems but resolution was not the issue that separated their substantially different technologies. It was patent interference lawsuits and deployment issues given the tumultuous financial climate of the late '20s and '30s.
The British 405-line system was the first to advertise itself as high definition and see widespread use. Most patents were expiring by the end of World War II leaving the market wide open and no worldwide standard for television agreed upon. The world used analog PAL, NTSC, SECAM and other standards for over half a century.
Contents |
[edit] French 819-line system
When Europe resumed TV transmissions after WWII, i.e. in the late 1940s and early 1950s, most countries standardized on a 625-line television system. The two exceptions were the British 405-line system, which had already been introduced in 1936, and the French 819-line system, introduced in 1948. The French TV system was arguably the world's first HDTV system, and, by today's standards, it could be called 755i. It was used only for France's first television channel, along with broadcasters in Belgium and Monaco. However, the theoretical picture quality far exceeded the capabilities of the equipment of its time, and each 819-line channel occupied a wide 14 MHz of VHF bandwidth.
When, in the late 1960s, a second TV channel and color TV were introduced in much of Europe, the UK adopted the 625-line system beginning with BBC Two in 1964. Likewise, despite some attempts to create a color SECAM version of the 819-line system, France abandoned it in favor of 625 (with the final 819-line transmissions from Paris in 1986)
[edit] Multiple sub-nyquist sampling Encoding system (MUSE)
(main article:Multiple sub-nyquist sampling Encoding system)
Japan had the earliest working HDTV system, with design efforts going back to 1979. The country began broadcasting analog HDTV signals in the early 1990s using an interlaced resolution of 1035 or 1080 active lines (1035i) or 1125 total lines.
The Japanese system, developed by NHK Science and Technical Research Laboratories (STRL) in the 1980s, employed filtering tricks to reduce the original source signal to decrease bandwidth utilization. MUSE was marketed as "Hi-Vision" by NHK.
- Japanese broadcast engineers immediately rejected conventional vestigial sideband broadcasting for well-founded technical reasons.
- It was decided early on that MUSE would be a satellite broadcast format as Japan economically supports satellite broadcasting.
In the typical setup, three picture elements on a line were actually derived from three separate scans. Stationary images were transmitted at full resolution.However, as MUSE lowers the horizontal and vertical resolution of material that varies greatly from frame to frame, moving images were blurred in a manner similar to using 16 mm movie film for HDTV projection. In fact, whole-camera pans would result in a loss of 50% of horizontal resolution.
MUSE's "1125 lines" are an analog measurement, which includes non-video "scan lines" during which a CRT's electron beam returns to the top of the screen to begin scanning the next field. Only 1035 lines have picture information. Digital signals count only the lines (rows of pixels) that have actual detail, so NTSC's 525 lines become 480i, and muse would be 1035i.
Shadows and multipath still plague this analog frequency modulated transmission mode.
Considering the technological limitations of the time, MUSE was a very cleverly-designed analog system. Though Japan has since switched to a digital HDTV system based on ISDB, the original MUSE-based BS Satellite channel 9 (NHK BS Hi-vision) is still being broadcast. It broadcasts the same programs as BS-digital channel 103, but will end sometime in 2007.
[edit] HD-MAC
(main article:HD-MAC)
HD-MAC was a proposed television standard by the European Commission in 1986 (MAC standard) . It was an early attempt by the EEC to provide HDTV in Europe. It was a complex mix of analogue signal (Multiplexed Analogue Components), multiplexed with digital sound. The video signal ( 1250 (1152 visible) lines/50 frames in 16:9 aspect ratio) was encoded with a modified D2-MAC encoder.
In the 1992 Summer Olympics, an experimental HD-MAC broadcasting took place. 100 HD-MAC receivers (in that time, retroprojectors) in Europe were used to test the capabilities of the standard. This project was financed by the EEC. The PAL-converted signal was used by mainstream broadcasters such as SWR, BR and 3Sat.
The HD-MAC standard was abandoned in 1993, and since then all EU and EBU efforts have focused on the DVB system (Digital Video Broadcasting), which allows both SDTV and HDTV.
[edit] See also
The analog TV systems these systems were meant to replace
Related standards
- NICAM-like audio coding is used in the HD-MAC system.
- Chroma subsampling in TV indicated as 4:2:2, 4:1:1 etc...
[edit] External links
- HDTV coverage of the Barcelona Olympic Games by M. Romero and E. Gavilan (EBU)
- The HDTV demonstrations at the Expo 92 by J.L. Tejerina and F. Visintin (EBU)
- European Broadcasting Union
- COUNCIL DIRECTIVE 92/38/EEC of 11 May 1992.
