IV YEAR ECE B SECTION TELEVISION AND VIDEO ENGINEERING BY G.SHANMUGAVADIVEL M.E., UNIT 1.
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Transcript of IV YEAR ECE B SECTION TELEVISION AND VIDEO ENGINEERING BY G.SHANMUGAVADIVEL M.E., UNIT 1.
IV YEAR ECE B SECTION
TELEVISION AND VIDEO ENGINEERING
BYG.SHANMUGAVADIVEL M.E.,
UNIT 1
2
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