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Introduction
Television was initially intended for sports, newsand entertainment application and was almostentirely distributed by terrestrial broadcasts.
Television is being distributed by other means,such as cable (fiber or coaxial), video tapes ordisks (analog or digital) and satellites (e.G. Directbroadcast).
Moreover, the television signal packaged forterrestrial broadcasting is very wasteful of thebroadcast spectrum and can benefit from modernsignal processing.
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Introduction to HDTV
Three current colour television standards- NTSC(National Television System Committee), PAL(Phase Alternating Line), and SECAM (SequentialCouleur Avec Memoirs) .
Common to the three HDTV standards arewidened aspect ratio (16:9 instead of 4:3),increased picture resolution, and audio of compactdisc quality.
High Definition Services -- invented in Japan .
In Europe, HD-MAC transmission via DBS wasdeveloped. The signal processing of HD-MAC
coding and decoding is digital.
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Introduction to HDTV
Transmission format is analog and suffers fromknown drawbacks.
The four proponents of HDTV are Digi Cipher byGI Corp. and MIT, DSC HDTV (Digital SpectrumCompatible) by Zenith and AT & T, AD-HDTV by
ATRC (Advanced Television Research Consortium,
consisting of Compression Lab. David Sarnoff
Research Center, Thomson Consumer Electronics,
North American Philips, and CCDC(Channel
Compatible Digi Cipher) by MIT and GI Corp.
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HDTV
HDTV-digital processing of TV signal both at thetransmitter and in the receiver.
The analog camera signal and sound signal are
first converted into digital form at the transmitter.
D/A converters are needed at the final stages ofthe receiver to change video and audio signals
from digital to analog form.
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HDTV
HDTV - Increased spatial and temporal resolutionIncreased image aspect ratio-clear Picture
Multi-channel CD-quality surround sound
Reduced artifacts
Bandwidth compression
Channel encoding to make better
utilization of terrestrial spectrumBetter interoperability with the evolving
telecommunications and computing
infrastructure.
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HDTV
Spatial resolution by approximately a factor oftwo in both the horizontal and vertical dimensions.
Picture-1000 scan lines and more than 1000
pixels per scan line .
The result of this is that the number of activepixels in an HDTV signal increases by about a
factor of five, with a corresponding increase in theanalog bandwidth.
Most HDTV systems specify the image aspectratio to be 16:9.
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HDTV
Each audio channel is independently compressed,and these closed captioning, teletext, encryption,
addressing, program identification and other data
services are in a layered fashion. Audio fidelity is nearly as good as that
obtainable from the current generation of CDs.
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HDTV In Various Countries
In the 1970s, the Japan Broadcasting Corporation(NHK) began to design the next generationtelevision system. The main systems work was
done by NHK, but the substantial infra-structureequipment required for a complete system (e.g.cameras, recorders and displays) was developedby other Japanese companies.
Although the European Broadcasting Union(EBUb), had given some indication of support forthe NHK-1125/60 system for professional studiouse, in 1986 the broadcasting and manufacturinginterests in Europe agreed on their own highdefinition standards, called HD-MAC.
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Problems Of Current Analog TV:
Inter-line flicker, line crawl and vertical aliasingare largely a result of interlaced scanning.
Large are flicker as seen from a close distance or
on large screens is due to our ability to resolvetemporal brightness variations at frequencies even
beyond 60Hz when the peripheral areas of vision
are engaged.
Computer displays employ much higher frame
rates (up to 72 Hz) to overcome large area flicker.
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Problems Of Current Analog TV:
Analog television, a number of artifacts arise, due
to transmission- ghosts, which are due to multiple
receptions of the same signal, cannot be entirely
removed from the analog signal. In digital HDTV,ghost cancellation can be done more successfully.
Static raster visibility is more apparent on larger
displays since viewers can make out individual scan
lines. Increased spatial resolution in HDTV will
reduce this effect substantially .
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