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
Early Camera Tubes
Electronic Scan (Camera Pickup Tube) Video Signal Electron Beam TargetLensObject
Differences Between Horizontal and Vertical Synch Pulses Rate Duration Vertical59.94/sec 1:3 Horizontal 15, /sec 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 1-9V-sync and Equalizing Pulses Lines 12-14SMPTE Time Code Lines 17-19VITS and VIRS Line 20Network 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 = = 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 GB
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 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
Color TV Transmitter
TV Frequency Allocations 2 - 4VHF-Lo 54 MHz - 72 MHz 5 - 6VHF-Lo 76 MHz - 88 MHz 7 – 13VHF-Hi174 MHz – 216 MHz 14 – 59UHF470 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
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 its history)
Television Transmission Systems Over-the Air Terrestrial Broadcasting
Antenna Systems Radio Energy in Space –300 million meters per second E = MC 2 Speed of Light
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.
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.
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.