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The term high definition once described a series of television systems
originating from August 1936; 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 ongoing competition between companies and
nations to create true "HDTV" spanned the entire 20th century, as each new
system became more HD than the last.
The British high-definition TV service
started trials in August 1936 and a regular service on 2 November 1936 using
both the (mechanical) Baird 240 line sequential scan (later to be inaccurately
rechristened 'progressive') and the (electronic) Marconi-EMI 405 line interlaced
systems. The Baird system was discontinued in February 1937.1 In 1938 France
followed with their own 441-line system, variants of which were also used by a
number of other countries. The US NTSC 525-line system joined in 1941. In 1949
France introduced an even higher-resolution standard at 819 lines, a system that
should have been high definition even by today's standards, but was monochrome
only and the technical limitations of the time prevented it from achieving the
definition of which it should have been capable. 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
"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 as the video baseband bandwidth was required to be not more
than 3 MHz.
Colour broadcasts started at similarly higher resolutions, first
with the US NTSC color system in 1953, which was compatible with the earlier
monochrome systems and therefore had the same 525 lines of resolution. European
standards did not follow until the 1960s, when the PAL and SECAM color systems
were added to the monochrome 625 line broadcasts.
The Nippon H¨s¨ Ky¨kai
(NHK, the Japan Broadcasting Corporation) began conducting research to "unlock
the fundamental mechanism of video and sound interactions with the five human
senses" in 1964, after the Tokyo Olympics. NHK set out to create an HDTV system
that ended up scoring much higher in subjective tests than NTSC's previously
dubbed "HDTV". This new system, NHK Color, created in 1972, included 1125 lines,
a 5:3 aspect ratio and 60 Hz refresh rate. The Society of Motion Picture and
Television Engineers (SMPTE), headed by Charles Ginsburg, became the testing and
study authority for HDTV technology in the international theater. SMPTE would
test HDTV systems from different companies from every conceivable perspective,
but the problem of combining the different formats plagued the technology for
many years.
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 US the Grand Alliance
proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were
based on the MPEG-2 standard, although DVB systems may also be used to transmit
video using 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, the world already having split into two camps, 25/50 Hz and 30/60 Hz,
largely due to the differences in mains frequency. The IWP11/6 working party
considered many views and throughout 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.
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