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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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