Transcript Video Basics - Castle of SARAVANESH J

Broadcast Basics
Week 13
ICS 620
BROADCAST BASICS
ICS 620
Week 13
Introduction
Video Basics (Analog Systems)
Transmission Systems
• Wireless (terrestrial)
• Wired (cable television)
Digital Video (Two Weeks)
Video Standards
• Standards and Principals
– Persistence of Vision
The rapid presentation of frames
of video information to give you
the illusion of smooth motion.
Frequency Standards
Frame Frequency
• 16 Frames per Second (fps) Black and
White
• 24 fps SOF
• Continuity of Action
• Problem of Flicker
– The gross alteration of light and dark
Frequency Standards
Field Frequency
• Frame Frequency x 2
• Continuity of Illumination
Film Vs. Video
• Film - Project a complete picture
• Video - Scan, line by line, at a high
rate of speed - 6 million bits per
second
How do we describe a picture?
• A picture element (“pel” or “pixel”) one
at a time
• For each pel we need to somehow
describe:
– Brightness (luminance)
– Hue (phase, “tint”)
– Saturation (color intensity, “chroma”)
Vertical Resolution
• The picture quality associated with
the number of dots (pixels) used to
construct the picture.
– 367,000 dots
– on 525 rows (vertical)
Film vs. NTSC Specs
Aspect Ratio
Camera Tubes
Early Camera Tubes
Image Orthicon
Electronic Scan
(Camera Pickup Tube)
Object
Lens
Target
Electron
Beam
Video Signal
Scanning
• Progressive
• Interlace/Offset
Interlace Example
NTSC: 525 lines, 30 frames/sec,
60 fields/sec
Picture Tube
Picture Tube
Picture Tube
Scanning a Focused Image
Progressive Scanning
Interlace Scanning
Sync Pulses
Differences Between Horizontal and
Vertical Synch Pulses
Rate
Vertical
Duration
59.94/sec
Horizontal 15,734.264/sec
1:3
3:1
Waveform Sketch of a Video Signal
A simple video waveform
One Line
Waveform of Sync Pulses
IRE Measurement Scale
Vertical Blanking Interval
(VBI)
• Lines 1-21 of each field
Vertical Interval Test Signal (VITS)
Vertical Interval Reference Signal (VIRS)
Lines 1-9
V-sync and Equalizing Pulses
Lines 12-14
SMPTE Time Code
Lines 17-19
VITS and VIRS
Line 20
Network Source Code (field 1)
Line 21
Closed captioning (field 1)
Kell Factor
The Ratio of effective resolution to
the theoretical resolution is known
as the Kell Factor.
Vertical Resolution Summary
• Max Lines/Frame = 525
• Lost for Vertical Blanking = 42
(21 lines per field)
• Visible = 525-42 = 483
• Kell Factor = 72.5%
• Effective Resolution = 350 lines
Horizontal Resolution Summary
(4.2 MHz Video Bandwidth)
= 4.2 cycles per microsecond
x 52 microseconds (active scan)
x 2 pixels per cycle
= 436 pixels per line
Television Transmission
• Picture Information
• Blanking pulses
• Sync pulses
• Audio information
What about Color?
Component Nature of Color
R
G
B
Video Color Palette
Color Television
R = Red
G = Green
B = Blue
B + G = Cyan
G + R = Yellow
B + R = Magenta
NTSC Color Bars
Block Diagram of Color Camera
Gamma G
A measurement of contrast, gamma
correction is required because the
brightness output of a camera does
not correspond to the brightness
recognition of the human eye.
Composite Color
• Y = Luminance Signal
Y =30% red + 59% green + 11% blue
• C = Chrominance Signal
C = I Q Matrix
Color Matrix
• Saturation = Amplitude of the I and
Q signals
• Hue = Phase developed by the
difference in amplitude between
the I and Q signals
Transmitter Tube
Color TV Transmitter
TV Frequency Allocations
2- 4
VHF-Lo
54 MHz -
72 MHz
5- 6
VHF-Lo
76 MHz -
88 MHz
7 – 13
VHF-Hi
174 MHz – 216 MHz
14 – 59
UHF
470 MHz – 746 MHz
NOTE: Natural breaks occur between channels 4 and 5; channels 6 and 7;
and channels 13 and 14. Each channel is 6 MHz wide.
NTSC Bandpass Characteristics
(Black and White)
Color TV Signal
NTSC Bandpass Characteristics
(Color)
Color TV Signal
Worldwide Standards
• National Television System
Committee - NTSC (1953)
• Phase Alternation Line -PAL
(1967)
• Sequentiel Couleur Avec Memoire
- SECAM (1967)
World TV Standards
World TV Standards
Principal TV Systems
FM Stereo Transmitter
Transmitter Output
• Main Channel (L + R)
• Stereo Channel (L - R)
• 19 kHz Pilot Sub-carrier
Stereo Multiplexing
• L+R Signal (Main Channel)
• L-R Signal (Stereo Channel)
• 19 kHz Pilot Subcarrier (FM)
The Math
(L + R) + (L - R) = 2 L
(L + R) + (- L + R) = 2 R
FM Stereo Receiver
Television Stereo
• Multi-channel Television Sound
(MTS)
• Used to provide Stereo on
conventional NTSC TV broadcast
(TV has been FM mono for most
of it’s history)
Television Transmission Systems
Over-the Air
Terrestrial Broadcasting
Antenna Systems
• Radio Energy in Space
–300 million meters per second
• E = MC2
• Speed of Light
Spectrum
Wavelength
• Lambda (meters)
• Velocity (300,000,000 meters/sec.)
• Frequency (Hz)
 = v/f
TV Station
WTHR-TV
Ch.13 (210-216 MHz)
WTHR-TV
WAVELENGTH IN:
A. Meters
B. Miles
C. Feet
WTHR Television - Channel 13
Indianapolis, Indiana
•
Channel 13 (210-216 MHz)
• 316 kw visual
• 63.2 kw aural
• 980t/1,039g
Television Factbook
47 CFR 73.603
Wavelength Example
WTHR Television
Meters:
Lambda = 300/211.25 = 1.46 meters
Miles:
Lambda = .186/211.25 = .00088 miles
Feet:
1 meter = 3.28 feet
Lambda = 1.46 meters x 3.28 = 4.79 feet
AM Station
• What is the height of
this AM station
antenna tower
operating at 540 kHz,
in meters and feet?
Propagation
• Radiation Patterns (Contours)
• AM - Tower as the Antenna
• FM/TV - Antenna on Tower
TV Propagation
TV Propagation Map
FM Propagation Map
KFMD-FM Denver
AM Tower
Side view
Top view
AM Directional Towers
AM Directional Propagation
Irregular Geographical
Patterns
•
•
•
•
Refraction
Reflection
Absorption
Interference
Why Directional Arrays?
• Co-Channel
• Adjacent Channel
• Other
Types of Waves
• Direct Waves (FM/TV)
• Ground Waves (AM)
– Radials
• Swampy Soil vs. Sandy Terrain
• Sky Waves (AM at night)
Types of Waves
Direct Waves
The primary path of the direct wave is from the
transmitting antenna to the receiving antenna. So, the
receiving antenna must be located within the radio
horizon of the transmitting antenna. Because direct
waves are refracted slightly, even when propagated
through the troposphere, the radio horizon is actually
about one-third farther than the line-of-sight or natural
horizon.
Direct Waves
Ground Waves
The Earth has one refractive index and the
atmosphere has another, thus constituting
an interface that supports surface wave
transmission. These refractive indices are
subject to spatial and temporal changes.
Ground Waves
Sky Waves
Sky waves, often called ionospheric
waves, are radiated in an upward direction
and returned to Earth at some distant
location because of refraction.
Sky Waves
Questions
and
Answers