Notes MS Lecture7

8/12/2019 Notes MS Lecture7

1/25

Multimedia Systems

Lecture - 7


2/25

2

Lecture Outline

Video

Analog TV

Analog Television Broadcast Standards

Digital TV Digital Television Broadcast Standards


3/25

3

Analog TV

Analog TV encodes televisionpictureand soundinformation and transmits it as an analog signal.

Examples of analog television systems are:

NTSC PAL

SECAM

Broadcasters using analog television systems

encode the signals using NTSC, PAL or SECAMencoding, and then modulate this encoded signalonto VHF or UHF carrier.


4/25

4

Analog TV

Ignoring color (handling), all TV systems work in

essentially the same manner.

The monochrome image seen by camera

(luminance component of color image) is divided

into horizontal scan lines, some number of which

make up a single image/frame.

All analog TV systems are interlaced, alternaterows of the frame are transmitted in sequence

followed by remaining rows in sequence.


5/25

5

Analog TV Standards by Regions


6/25

6

NTSC -National Television System Committee

It is the analog television system used in most of

North America, South America, Japan, South

Korea, and some other Pacific regions.

NTSC is also the name of the U.S. standardization

body that developed the broadcast standard.

The first NTSC standard, developed in 1941 had no

provision for colour TV. The second version, adopted in 1953, allowed color

broadcast compatibility with existing receivers.


7/25

7

NTSC

NTSC uses YIQ color model.

Quadrature modulation is used to combine I & Q toproduce a single chroma signal.

Composite signal is formed by

Fsc is 3.58MHz.

The available bandwidth is 6MHz, in which the audio issignal centered at 5.75MHz and the lower spectrumcarries picture information


8/25

8

NTSC -National Television System Committee

NTSC signal is an interlaced video signal with

262.5 lines per field (525 scan lines per frame)

60 fields per second (30 frames per second)

4:3 aspect ratio Out of these 525 scan lines

485 make up the visible raster (active lines)

The remaining 20 lines are blanked for vertical retrace and

synchronization. Blanking pulses are inserted during the retrace intervals to blank

out retrace lines on CRT and Sync pulses ensure that picture

starts at the top left corner of the receiving CRT.


9/25

9

PAL - Phase Alternate Line

PAL is an analog television system used in most part of

western Europe, most part of Asia and other countries

It was developed in 1960s (in western Europe) to

overcome the weakness related to colour reproductionthat existed in NTSC.

PAL is also interlaced like NTSC. Itconsists of

625 lines per frame


Both PAL and SECAM have better color reproduction

than NTSC.


10/25

10

PAL

PAL uses YUV color model.

Uses an 8 MHz channel and allocates a bandwidth

of 5.5 MHz to Y, and 1.8 MHz each to U and V.

In PAL, the phase of part of the colour

information on the video signal is reversed with

each line, which automatically corrects phase

errors in the transmission of the signal bycancelling them out


11/25

11

SECAM - SEquential Couleur Avec Memoire

SEquential Couleur Avec Memoire is French for

"Sequential Color with Memory

It is historically the first European color TV

standard, developed in France in 1960s.

SECAM is also interlaced andconsists of

625 lines per frame



12/25

12

SECAM

SECAM differs from the other systems by the way thechrominance (R-Y and B-Y) signals are carried.

First, SECAM uses frequency modulation to encodechrominance information on the sub carrier.

Second, instead of transmitting the red and blueinformation together, it only sends one of them at a time,and uses the information about the other color from the

preceding line.

It uses a delay line (an analog memory device), forstoring one line of color information.

This justifies the "Sequential, With Memory" name.


13/25

13

Summary of the Analog TV Standards

fps lines Band-

width

(MHz)

B&W

Mod.

Colour

Mod.

Audio

Mod.

NTSC 30 525 6 AM QAM FM

PAL 25 625 7-8 AM QAM FM

SECAM 25 625 7-8 AM FM FM


14/25

14

PAL Vs. NTSC

The basics of PAL and the NTSC system are very similar; aquadrature amplitude modulated subcarrier carrying thechrominance information is added to the luminance videosignal to form a composite video baseband signal.

The frequency of this subcarrier is 4.43361875 MHz for PAL,compared to 3.579545 MHz for NTSC.

The SECAM system, on the other hand, uses a frequencymodulation scheme on its two line alternate colour subcarriers4.25000 and 4.40625 MHz.

NTSC receivers have to perform tint control for manual colourcorrection. If not adjusted correctly, the colours may be faulty.

The PAL standard on the other hand, automatically removeshue errors by utilising phase alternation of the colour signal.


15/25

15

PAL Vs. SECAM

SECAM also tries to resolve the NTSC hue problem.

It does so by applying a different method to colourtransmission, namely alternate transmission of thechrominance signals and frequency modulation, while

PAL attempts to improve on the NTSC method. SECAM transmissions are more robust over longer

distances than NTSC or PAL.

However, owing to their FM nature, the colour signalremains present, although at reduced amplitude, even in

monochrome portions of the image, thus being subject tostronger cross colour.

Like PAL, a SECAM receiver needs a delay line.


16/25

16

Digital TV Systems

Digital TV systems transmit audio and video bydiscrete signals (in contrast to analog signals inanalog TV systems)

Switching from analog to digital TV began in 2006

in Europe and as of late 2009, ten countries haveturned off their analog terrestrial broadcasting.

Two principle digital broadcasting systems are

ATSC

DVB

Other systems used are:

ISDB, DMB-T/H


17/25

17

Digital terrestrial TV systems by regions


18/25

18

ATSCAdvanced Television Systems

Committee

The ATSC terrestrial broadcast standard was

developed by the Advanced Television Systems

Committee and adopted as a standard in U.S. and

Canada. ATSC is inferior to other digital systems in

dealing with multipath interference; however it is

better at dealing with impulse noise. ATSC also supports satellite and cable television

systems.


19/25

19

ATSC

ATSC-T (not an official term)

The terrestrial ATSC uses 8-VSB (vestigial sideband)

modulation technique and supports 19.39 Mbit/s digital

data stream. ATSC-C (not an official term)

On cable, ATSC uses 256QAM (some use 16VSB)

modulation with a throughput of 38.78 Mbit/s.


20/25

20

DMBT/H

Digital Multimedia Broadcast - Terrestrial/

Handheld is the digital television standard of

China, Hong Kong and Macau.

It is now called DTMB (Digital TerrestrialMultimedia Broadcast).

This is a hybrid system, part of which is ATDB;

very similar to ATSC.


21/25

21

DVB-Digital Video Broadcast

DVB-T

DVB terrestrial system uses coded OFDM (COFDM)

which uses as many as 8000 independent carriers each

transmitting data at low rate. It provides superior immunity to multipath

interference.

It has system variants that allow data rates from

4Mbit/s up to 24Mbit/s.


22/25

22

DVB-Digital Video Broadcast

DVB-S

It is the original DVB standard for satellite television.

It transmits MPEG-2 audio/video stream.

DVB-C

It is the DVB (European) standard for the broadcast of

digital television over cable.

It transmits an MPEG-2 digital audio/video streamusing QAM modulation with channel coding.


23/25

23

ISDBIntegrated Services Digital Broadcasting

ISDB is very similar to DVB; however itcomprises of 13 subchannels.

12 subchannels are used for TV, while the last one

serves as either guard band or for the 1seg service. It was developed in Japan with MPEG-2 as (video

and audio compression standard) and now used inBrazil with MPEG-4.

Types of ISDB differ mainly in modulations used ISDB-T

ISDB-S


24/25

24

HDTV

High-definition television(HDTV, or just HD)

refers to video having resolution substantially

higher than traditional television systems

(standard-definition TV, or SDTV, or SD). HD has one or two million pixels per frame,

roughly five times that of SD.

Early HDTV broadcasting used analogtechniques, but today HDTV is digitally broadcast

using video compression.


25/25

25

HDTV

HDTV uses different formats for transmission,

amongst which: 1280 720 pixels in progressive

scan mode (abbreviated 720p) or 1920 1080

pixels in interlace mode (1080i). HDTV has much wider aspect ratio of 16:9 as

compared to 4:3 for standard TV.

The flat panel Plasma and LCD TVs are HDTVs.

Notes MS Lecture7

Documents

Transcript of Notes MS Lecture7