Analog high-definition television system
Analog high-definition television was an analog video broadcast television system developed in the 1930s to replace early experimental systems with as few as 12-lines. On 2 November 1936 the BBC began transmitting the world's first public regular analog high-definition television service from the Victorian Alexandra Palace in north London. It therefore claims to be the birthplace of television broadcasting as we know it today. 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 1920s and 1930s.
Most patents were expiring by the end of World War II leaving no worldwide standard for television. The standards introduced in the early 1950s stayed for over half a century.
UK 405-line system
When the UK introduced 405-line television broadcasting in 1936, it was described as 'high definition television'. By today's standards it can't be described as "high definition". The description merely referred to its definition in comparison to the early 30-line (largely) experimental system broadcast in the 1920s.
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 576i (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. During the 1940s René Barthélemy already reached 1015-lines and even 1042-lines. On November 20, 1948, François Mitterrand, the then Secretary of State for Information, decreed a broadcast standard of 819-lines developed by Henri de France; broadcasting began at the end of 1949 in this definition.
This was arguably the world's first high-definition television system, and, by today's standards, it could be called 737i (as it had 737-lines active) with a maximum theoretical resolution of 408×368-line pairs (which in digital terms can be expressed as equivalent to 816×736 pixels) with a 4:3 aspect ratio (and thus a slightly wide effective "pixel aspect ratio" of 6:5, square pixel recording needing approx 980x736 instead). It was used only in France by TF1, and in Monaco by Tele Monte Carlo. 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.
By comparison, the modern 720p standard is 1280×720 pixels, of which the 4:3 portion would be 960×720 pixels, while PAL DVDs have a resolution of 720×576 pixels.
Television channels were arranged as follows:
|Ch||picture (MHz)||sound (MHz)|
Technical specifications of the broadcast television systems used with 819-lines.
|Field frequency||Active picture||Field blanking||No. of broad pulses||Broad pulse width||Line frequency||Front porch||Line sync||Back porch||Active line time||Video/syncs ratio|
|50 Hz||737-lines||41-lines||1 per field||20.0 µs||20475 Hz||0.5 µs||2.5 µs||5.0 µs||40.8 µs||70/30|
|System||Lines||Frame rate||Channel bandwidth (in MHz)||Visual bandwidth (in MHz)||Sound offset||Vestigial sideband||Vision mod.||Sound mod.|
|System E||819||25||14||10||±11.15 (Sound carrier separation +11.15 MHz on odd numbered channels, -11.15 MHz on even numbered channels.)||2.00||Pos.||AM|
System E implementation provided very good (near HDTV) picture quality but with an uneconomical use of bandwidth; a 625/50 signal providing the same clarity as an 819-line image, but matted down 4:3 with the same number of lines, would still need nearly 6mhz for the vision carrier alone (vs typical 5 to 6mhz in actual use), and 5mhz for 525/60 (vs typical 4.2mhz), although a 405/50 transmission could get away with only 2.5mhz (typical 3mhz, as System A made no allowance for Kell Factor and thus had a "narrow pixel"/"tall line" appearance). Thus even an unusually crisp "standard" definition (or slightly soft 405-line) image only needed half, or even one-quarter the vision bandwidth of the 819-line system to give a "balanced" appearance, despite their lower overall resolution still seeming perfectly clear on the more affordable small-screen receivers often used in the pre-color era. With the usual additions of sound carrier and vestigial sideband the result was a combined signal that demanded approximately two to three times the bandwidth of more moderately specified standards, even when colour was added to them (as the color subcarrier resides within the luma signal space).
System F was an adapted 819-line system used in Belgium and Luxembourg as an answer to this problem, with only half the vision bandwidth and approximately half the sound carrier offset. It allowed French 819-line programming to squeeze into the 7 MHz VHF broadcast channels used in those neighbouring countries, albeit with a substantial loss of horizontal resolution (408×737 effective, with what would now be considered extra-wide 12:5 aspect ratio pixels); although this still offered approximately twice the actual clarity of 405-line System A (twice the lines, roughly the same horizontal definition), the contrast between vertical and horizontal resolution would have made it seem perceptually worse. Use of System F was discontinued in Belgium in February 1968, and in Luxembourg in September 1971.
Despite some attempts to create a color SECAM version of the 819-line system (which would have then also had the highest pre-HDTV colour signal resolution, with lines of FM encoding alternately centred on 8.82 and 8.5mhz, if arranged similarly to 625-line SECAM), France abandoned it in favor of the Europe-wide standard of 625-lines (576i50), with the final 819-line transmissions from Paris in 1984. TMC in Monaco were the last broadcasters to transmit 819-line television, closing down their System E transmitter in 1985.
However, between 1976 and 1981 when French channel TF1 was switching area by area to the new analog 625-lines UHF network with SECAM color, some transmitters and gapfillers broadcast the 819-line signal in UHF. When switching to 625-lines, most gapfillers did not change UHF channel (e.g. many gapfillers using this transmission located in French Alps near Grenoble, Mont Salève and Geneva began broadcasting on UHF channel 42, and continue to use this frequency to this day). They were switched to 625-lines in June 1981.
Multiple sub-nyquist sampling Encoding system (MUSE)
Japan had the earliest working HDTV system, with design efforts going back to 1979. The country began broadcasting wideband analog high-definition video signals in the late 1980s using an interlaced resolution of 1035 or 1080-lines active (1035i) or 1125-lines total supported by the Sony HDVS line of equipment.
The Japanese system, developed by NHK Science & Technology Research Laboratories 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 rejected conventional vestigial sideband broadcasting.
- 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) of the picture makeup as there are no other scanning lines (though conversion to an analogue format will introduce them), 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) was still being broadcast as of 2007[update]. It broadcast the same programs as BS-digital channel 103, but transmission ended on November 30, 2007.
Subsampling lives on in modern MPEG systems based on JPEG coding, as JPEG offers Chroma sub-sampling. High quality HD television has a sampling structure approximating 4:2:1 (Luma : Chroma : Saturation) for reference images (I-Frames), though 4:0.75:0.65 is probably typical for multi-channel delivery.
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 analog signal (Multiplexed Analog 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 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 European Union (EU). The PAL-converted signal was used by mainstream broadcasters such as SWR, BR and 3Sat.
The analog TV systems these systems were meant to replace
- NICAM-like audio coding is used in the HD-MAC system.
- Chroma subsampling in TV indicated as 4:2:2, 4:1:1 etc...
- http://819lignes.free.fr/index.html Restore operation on a French 1951 TV set (French language only)
- 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.