High-definition television: Encyclopedia II - High-definition television - Early systems

High-definition television - Early systems

High-definition television - SECAM 755i

When Europe resumed TV transmissions after WWII, i.e. in the late 1940s and early 1950s, different countries used different resolutions. The UK used 405 lines, most other countries 625 lines (both numbers include the vertical gap, the actual resolution were lower), but France decided in 1948 to go for 819 lines. The French TV system thus became the world's first HDTV system, and by today's standards, the French system could be called 755i (not all lines could be used for the actual image — some lines were lost during the vertical retrace). The French 819-line (or 755i) HDTV system was introduced in the 1950s. When, in the late 1960s, a second TV channel and color TV were introduced in Europe, the UK dropped its 405-line TV system (completely in 1985) and France dropped its 819-line system, making all European countries agree to use 625 lines (576i) for their TV transmissions.

The French "755i" 819-line HDTV system was used only in France and in Monaco, and in France only for the first French TV channel. It was discontinued in 1986. It was used only for black-and-white TV; color TV in 819-line SECAM never went beyond the experimental stage. It was transmitted only on VHF channels, and a French 819-line TV channel occupied 14 MHz of bandwidth.

High-definition television - MUSE

Japan has the earliest working HDTV system still in use, with design efforts going back to 1979. Japan began broadcasting analog HDTV signals in the early 1990s using an interlaced resolution of 1035 lines (1035i). The Japanese MUSE 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.

• Typically three picture elements on a line were actually derived from three separate scans. Moving images were thus blurred in a manner similar to using 16mm movie film for HDTV projection.
• Stationary images were transmitted at full resolution.
• Whole camera pans would result in a loss of 50% of horizontal resolution.
• Considering the technological limitations of the time, MUSE was a very cleverly designed analog system.
• MUSE had a bit-reduced stereo audio transmission system that was notable in its design as it was not psychoacoustical like Musicam.

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.

High-definition television - HD-MAC

The European Commission established a European standard for uncompressed digital HDTV in a 1986 directive (MAC). However, it never became popular among broadcasters. It was required that all high-powered satellite broadcasters used MAC from that year. Owing to the advance of technology and the launch of middle powered satellites by SES Astra, broadcasters could avoid MAC, and lower transmission costs. HD-MAC (the high definition variant of MAC) was left for transcontinental satellite links, though.

Another reason for HD-MAC's failure was that it was not realistic to use 36 MHz for a high definition signal in terrestrial broadcasting (SDTV uses 6, 7 (VHF), or 8 MHz (UHF)). HD-MAC could only be used by cable and satellite providers, where there is a wider bandwidth available. Thus, analogue HDTV could not replace conventional SDTV (terrestrial) PAL/SECAM, making HD-MAC sets unattractive to potential consumers.

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.

See also: COUNCIL DIRECTIVE 92/38/EEC of 11 May 1992.

Adapted from the Wikipedia article "Early systems", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki