The term high definition once described a series of television systems originating from the late 1930s; 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 British high definition TV service started trials in August 1936 and a regular service in November 1936 using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937. In 1938 France followed with their own 441 line system, which was also used by a number of other countries. The US NTSC system joined in 1939. In 1949 France introduced an even higher resolution standard at 819 lines, a system that would be high definition even by today’s standards, but it was monochrome only. All of these systems used interlacing and a 4:3 aspect ratio except the 240 line system which was progressive (actually described at the time by the technically correct term of ‘sequential’) and the 405 line system which started as 5:4 and later changed to 4:3. The 405 line system adopted the (at that time) 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.
Color broadcasts started at similar “high” resolutions, first with the US’s NTSC color system in 1953, which was compatible with the earlier B&W systems and therefore had the same 525 lines of resolution. European standards did not follow until the 1960s, when the PAL and SECAM colour systems were added to the monochrome 625 line broadcasts.
Since the formal adoption of Digital Video Broadcasting‘s (DVB) widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as “standard definition” television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.
In 1958, the Soviet Union created Тransformator (Russian: Трансформатор, “Transformer”), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of television conferences among military commands; as it was a military product, it was not commercialized.
In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard. The system, known as Hi-Vision or MUSE after its Multiple sub-Nyquist sampling encoding for encoding the signal, required about twice the bandwidth of the existing NTSC system but provided about four times the resolution. Satellite test broadcasts started in 1989, with regular testing starting in 1991 and regular broadcasting of BS-9ch commenced on 25 November 1994, which featured commercial and NHK programming.
In 1981, the MUSE system was demonstrated for the first time in the United States. It had the same 5:3 aspect ratio as the Japanese system. Upon visiting a demonstration of MUSE in Washington, US President Ronald Reagan was most impressed and officially declared it “a matter of national interest” to introduce HDTV to the USA.
Several systems were proposed as the new standard for the USA, including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirements. At the same time that the high definition systems were being studied, the number of television channels was growing rapidly and bandwidth was already a problem. A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV.
Rise of digital compression
Since 1972 International Telecommunication Union‘s radio telecommunications sector (ITU-R) ITU-R has been working on creating a global recommendation for Analogue HDTV. These recommendations however did not fit in the broadcasting bands which could reach home users. The standardization of MPEG-1 in 1993 also lead to the acceptance of recommendations ITU-R BT.709. In anticipation of these standards the DVB organisation was formed, an alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees on specifications which are formally standardised by ETSI.
DVB created first the standard for DVB-S digital satellite TV, DVB-C digital cable TV and DVB-T digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the USA the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirements.
In 1983, the International Telecommunication Union‘s radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their main electrical supplies.
The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.
Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has been suggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy ratio, and 2.35:1, the widest cinema format in common use, in order to minimize wasted screen space when displaying content with a variety of aspect ratios.)
An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC‘s R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 (“Rec. 709“) includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines). The current BBC freeview trials of HD use MBAFF, which contains both progressive and interlaced content in the same encoding.
It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an “enhanced” television format rather than a true HDTV format, and so was not included, although 1920×1080 and 1280x720p systems for a range of frame and field rates were defined by several US SMPTE standards.)
Demise of analog HD systems
However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK’s MUSE required over four times the bandwidth of a standard-definition broadcast, and despite efforts made to shrink the required bandwidth down to about two times that of SDTV, it was still only distributable by satellite with one channel shared on a daily basis between seven broadcasters. 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 broadcast analog HDTV. Digital HDTV broadcasting started in 2000 in Japan, and the analog service ended in the early hours of 1 October 2007.
In Europe, analogue 1,250-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.