IV YEAR ECE B SECTION

TELEVISION AND VIDEO ENGINEERING

BYG.SHANMUGAVADIVEL M.E.,

UNIT 1

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UNIT-1 FUNDAMENTALS OF TELEVISION

• Television System and scanning Principles: Sound and picture transmission- scanning process, video signals, characteristics of human eye, brightness perception and Photometric qualities,

• Aspect ratio and Rectangular scanning, persistence of vision and flicker, vertical resolution, Kell factor, Horizontal Resolution and video bandwidth, Interlaced scanning.

• Camera tubes- camera lenses- auto focus systems, camera pick up devices, Image orthicon- vidicon - plumbicon- silicon diode array vidicon –CCDsolid state image scanners - Comparison of Camera tubes-

• camera tube deflection unit- video processing of camera signals- color television signals and systems

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AIM & OBJECTIVE

• To Study the Fundamentals of Television and

how the Signals are transmitted and received

over a Long Distance and also working

principle of Camera Tubes and their types.

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Radio Spectrum

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190.5cm (75) Full HD 3D Smart Slim LED TV, USB Movie, HDMI, All Share, Built-in WiFi, 6D sound

UA75ES9000R MRP Rs. 750,000/-* Rating is 5 out of 5 stars .

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APPLICATIONS

• Broadcast Television

• Videography

• Genome TV

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DEFINITION OF TELEVISION

• Tele

- Distance• Vision

- Seeing

“Seeing from a long Distance”• Broadcasting

- To send in all direction

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Cont.,

• Picture (or) Scene

- Optical in Nature• Camera Tubes

• Picture Tubes

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Television System and Scanning Principles

• Sound transmission

• Picture transmission

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SOUND TRANSMISSION• Mechanical Waves

• Frequency Range

• Microphone

• Radio Frequency

• Feed the RF Energy

• Amplifier

• Sound Reproducing Device

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PICTURE TRANSMISSION

• Not Simple

• Space and Time of Brightness

• Retina

• Optical Nerves

• Sequential “Scanning” Technique

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Scanning process

• movement of electron beam spot

• 525 horizontal scans in a frame

• Horizontal scanning frequency

• 25-30 frames in one second (15625 lines )

• Starts upper left of the picture area known as line1

• Beam then proceeds horizontally to the upper right

edge at a precise rate

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Scanning a Frame

• The movement of electron beam spot from left to right

Vertical(Slower)

Horizontal(Faster)

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TYPES OF SCANNING

• Horizontal Scanning

– The movement of electron beam spot from left to right.

• Vertical Scanning

– The number of views also called fields transmitted per second.

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Cont.,

• The left edge to a point 2 lines below the previous

scan

• 52.5 microseconds to scan from left to right end

• 11 microseconds to return to the left again to

begin scanning the next line

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CAMERA PICK-UP DEVICES

• Lens System

• Photosensitive target

• Faceplate of Camera pickup tube

• Accurate and Well Defined Image

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PHOTOELECTRIC CONVERSION

• variations in the intensity of Light - Variations in Electric Signals

• Photoemissive Surfaces– Iconoscope

• Photoconductive Coating (or) Layer– Vidicon and Plumbicon

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VIDEO SIGNAL

• Picture Signal (25Hz -5MHz)

• Time Varying Electrical Signal Voltage

• Special Distribution of Brightness

• Frequency– Scanning Speed– Variations in the brightness

• Fast Scanning Rate

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Characteristics of human eye

• Visual acuity or Resolution– Ability to Resolve Finer Details in a picture

• Persistence of Vision

• Brightness and Colour Sensation

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Cont.,

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Cont.,

• Retina – Rod and Cones– Primary Brightness Level– Colour Perception

• 6,500,000 Cones

• 100,000,000 Rods

• 800,000 Optic Nerve Fibres

• Sharpest vision - Fovea

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Transmitter

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Receiver

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Vertical Resolution

• Proportional to # of vertical scan lines

• Theoretic maximum

– Half of visible scan lines

– Black lines alternate with white

• max. line pairs = video lines / 2

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Vertical Resolution

• Actual limit lower than theoretical~ 10% of lines

occur during retrace

• Returning beam from bottom to top of

image

• Scan lines may not perfectly synchronize

to high resolution object

– Typically 525 lines yield ~185 line pairs

Vertical Retrace

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Bandwidth

Bandwidth = [Horizontal Resolution] X [Video Lines] X [Frame Rate]

cycles------------scan line

lines--------- frame

frames--------- sec

cycles---------- sec

= X X

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Horizontal Resolution

Bandwidth

[Horizontal Resolution] = -------------------------------------------

[Video Lines] X [Frame Rate]

Bandwidth = [Horizontal Resolution] X [Video Lines] X [Frame Rate]

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TV Interlacing

• Frame scanned in two passes, first the odd

lines then the even

– One frame takes 1/30th second

– avoids flicker

• Each pass called a field

– takes 1/60th second

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• FRAME: An image created by 2 successive fields

• 2 fields = one frame • Field 1 scans all the odd numbered lines • Field 2 scans all the even numbered lines1st Field (Odd lines) 2nd Field (Even lines)

=

+ = One Frame

1/60th sec. 1/30th sec.1/60th sec.

+

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Interlaced Frame

• Sweeps the image as two fields that are

interlaced to form a given frame

• Field one

• Field two

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Cont.,

• Aspect Ratio

Ratio of width to Height of the picture image

• Retrace

– Horizontal retrace

• beam returned to left side of screen

– Vertical retrace

• beam returned to the top of screen

– Turns off video during retrace Vertical Retrace

Horizontal Retrace

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Example

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• Converts light to coded electrical signal

• Camera TubeVidicon

• cheapest / compact / laggy

Plumbicon• enhanced vidicon /

less lagCCD

• Semiconductor• not a tube

Camera Tubes

TVCamera

Light

electricalsignal

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Vidicon TV Pick-up Tube

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Image Orthicon

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Plumbicon

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Charge Coupled Device (CCD)

• Semiconductor device– not vacuum tube

• Stores charge in small discrete wells• Transfers charge to readout device one

line at a time• No readout beam, focusing or deflection

coils• Shorter than vidicons• Resolution limited by number of scan lines

(element array)

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Colour Fundamentals

Primary colors Secondary colors

• Red, Green, and Blue are primary colors

• Magenta, Yellow, and Cyan are secondary colors

• White is the combination of all colors

• Black is the absence of light

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Colour Fundamentals

Additive Colours Subtractive

Colours

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Basic Colour Properties

• Luminance or brightness: Amount of light

received by eye regardless of colour

Hue(color itself): Predominant spectral purity of

colour light

Saturation: intensity of the color

• Chrominance: combination of hue and saturation

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Chromaticity Diagram

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Colour circle

CAMERA TUBES

Vidicon Plumbicon Saticon Newvicon Chalnicon Silicon Diode Array

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VIDICON

Small Size

Principle

Target Plate – Intensity of Light

Construction1. Photo Conductive Target Plate

2. Scanning Section

3. Electron Gun Section

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PHOTO CONDUCTIVE TARGET PLATE

Antimony or Selenium Compounds

Face Plate – Transparent, Conductive Film

Signal Electrode

DC Supply

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SCANNING SECTION

Electron Beam

Deflection Coil

Alignment Coil

Deaccelerating Field (Grid No 4)

• Secondary Emission

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ELECTRON GUN SECTION

Heater

Cathode

Control Grid

Focusing Coil

Accelerating Anodes

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Principles

Photo Conduction 0.0001cm – 20MOhm2MohmPattern of Positive Potential – Photo LayerCharge Image High Illumination - +39VLow Illumination - +35V on the Beam Side

Leaky CapacitorCapacitor with Light dependent Resistor+40vElectrons – Unterminate end of CapacitorLoad Resistance

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Cont.,

Advantages Resolution is High

Long Life and Small in Size

Vary Target Voltage – Different Levels of Sensitivity

Gamma Cancellation Circuit is not necessary

Disadvantages High Dark Current

Poor Sensitivity

High Image lag

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PLUMPICON

►Outer Surface – SnO2 (Tin Oxide)

►Inner Surface – Pure Pb0 (Lead Monoxide)

►Outer Surface – Dopped Pb0

►15 * 10-6

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WORKING PRINCIPLE

►Capacitor – Reverse Bias Light Dependent

Resistor

► +40V Supply

►Reverse Bias – High Resistance

►Current & Voltage - RL

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Cont.,

► ADVANTAGES Reduced Lag

Higher Sensitivity

Medium Size & Compact

► DISADVANTAGES High Cost

Spectral Response is Poor for Red Colour Region

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SILICON DIODE ARRAY

• Vidicon

• N- type Silicon Wafers

• Trade name

• SiO2 - Insulating Layer

• Etching & Masking Process

• 0.003 cm & 1.5 cm – 540*540 photo diodes

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• ADVANTAGE– Low Dark Current

– Good Resolution

– High Sensitivity

– Long Life & Lightly Overloaded

• DISADVANTAGE– Speed of response is not good

– Dark Current is temperature Dependent

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SOLID STATE IMAGE SCANNERS

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CCD IMAGE SENSORS

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PMT Film CCD CMOSDynamic Range >1000 <100 >10,000 >5,000Detection Speed fastest slow slow fastQuantum Efficiency 5-20% 5-20% 25-95% 15-35%Multi-channel no yes yes yesReal-time yes no yes yesSpectral Sensitivity 300-900nm200-

1300nm 300-1100 400-1100Dark Signal good poor best bestRead Noise good good best best

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• CCD• Image Plate

• ADVANTAGES– No Need of Electron Gun &n Electron Beam

– No need For High Voltage

– No need for Vaccum Envelope

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Comparison of camera tubes

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S.No Characteristics Image Orthicon Vidicon Plumbicon

1Light Transfer Emission Based Photo Conductive Photo Conductive

2Sensitivity Very High High High

3S/N ratio 80 db 50 db 50 db

4Speed No Halo lag High halo lag Low Halo lag

5Spectral response Equivalent to eye Good Less in Red

6Operation Bit tough Easy Easy

7Cost High Low Bit High

8Size Big Small Medium

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Pick up tube deflection unit

Focusing Coil Axial Magnetic Field Divergent Electrons Focus Nodes or Lobes

Deflection Coil Pair Of Coils Vertical Field & Horizontal Field 1/10 th of the Focusing Coil

Alignment Coil Outside the Limiting Aperture Magnetic Field at right angles

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Deflection coil unit data

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VIDEO PROCESSING OF CAMERA SIGNALS

• Video Signal – Target Plate

• Pre – Amplifier– 300 nA– Head Amplifier– Cable Equalizer

• Co-Axial Cable

• Loss Of High Frequency – Passive Equalizer Network

• Length of Cable

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Aperature Correction & Image Enhancement

• Aperature Correction – Restore the Depth Of Modulation

– 400 lines- 40 lines Resolution

• Image Enhancement– A Delay Line Transversal Filter

– High Frequency boost Without Phase shift

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GAMMA CORRECTION

• Gamma =1 • Gamma < 1 – Low Upwards• Gamma > 1 – Low Downwards

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Clampling circuits

– DC Component

– AC Coupled Amplifier

– RESTORER

• White Clip– Normal Amplitude

• 1V (0.7 – 0.3)• 0.7 V – 100 IRE Units• 0.3 V – 40 IRE Units

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White clip

• Black Clipper– Blanking Adder

• Sync Adder– Sync Mixer or Adder Circuit

• Shading Correctors

• Polarity Reversal

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Colour television signals & systems

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Colour fundamentals

Primary colors Red, Green, and Blue

Secondary colors Magenta, Yellow, and Cyan

• White is the combination of all colors

• Black is the absence of light

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Cont.,

Additive Colours Subtractive

Colours

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Basic Colour Properties

• Luminance or brightness: Amount of light

received by eye regardless of colour

Hue(color itself): Predominant spectral purity of

colour light

Saturation: intensity of the color

• Chrominance: combination of hue and saturation

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Chromaticity Diagram

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Colour circle

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Possible 2 marks1. Mention the major function of the camera

tube?

2. What do you refer by persistence of eye?

3. Define visual acuity?

4. Define aspect ratio?

5. Define luminous intensity?

6. what do you mean by resolving power or resolution?

7. Mention some important characteristics of human eye?

8. Define luminance?

9. What do you understand by illuminance

10. Define luminous flux?

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11.What are rods and cones?

12.Give the relationship between eye parameters?

13.How will you solve the flickering problem?

14.What do you mean by interlaced scanning?

15.Why is scanning necessary in television system?

16.What do you understand by flicker?

17.Define vertical resolution?

18.What is horizontal resolution?

19.State grassman’s law.

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21. Explain the significance of generating colour difference signals

22. Define peak-white level?

23. What is the main function of the blanking pulses?

24. What do you understand by Hue?

25. Define Brightness.

26. What do you mean by saturation?

27. List any three requirements to be satisfied for compatibility in television systems.

28. What are per the post equalizing pulses?

29. What is additive mixing?

30. What is meant by video signal?

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31.What is meant by Luminosity

32.Define Rectangular Scanning

33.What is Focal Length & Power?

34.Give the Formula for Viewing angle Of Lens?

35.Define Lens Speed & Depth of Field?

36.What is Clamping Circuits?

37.What is Gamma Correction?

38.Define Polarity Reversal