CHAPTER 5:FUNDAMENTAL CONCEPTS IN VIDEO
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TYPES OF VIDEO SIGNALS
Component video
Higher-end video systems make use ofthree separate video signals for the red,green, and blue image planes.
This kind of system has three wires andconnectors connecting the camera orother devices to a TV or a monitor.
Use component video to take advantageof the superior picture found in suchsignal sources as HDTV and progressiveDVD
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TYPES OF VIDEO SIGNALS
Composite video
Color (“chrominance") and intensity(“luminance") signals are mixed into asingle carrier wave.
This is the type of signal used bybroadcast color TVs; it is downwardcompatible with black-and-white TV.
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TYPES OF VIDEO SIGNALS
S-video
Also known as Separated-Video or Super-video
A video color format that combines the three YUV video signals into twochannels. Brightness/luma (Y) is in one channel, and color/chroma (U and V)are in another. S-video provides a sharper image than composite video, but isnot as good as component video.
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BASIC VIDEO PROPERTIES
Representation of Video Signals
Visual Representation
To present the observer with as realistic as possible arepresentation of a scene
Transmission of Video Signals
Television Systems
Video Digitization
Digital Television
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VISUAL REPRESENTATION
•In order to accurately convey both spatial and temporal aspects of a scene,the following properties are considered
1.Vertical Details and Viewing Distance
•The geometry of a television image is based on the ratio of the picturewidth W to the picture height H (W/H), called the aspect ratio.
–Conventional aspect ratio is 4:3.
•The angular field of view is determined by the viewing distance, D,and is calculated as D/H.
2.Horizontal Detail and Picture Width
–Can be determined from the aspect ratio
3.Total detail content of a picture
–Since not all lines (horizontal and vertical) are visible to the observer,additional information can be transmitted through them.
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VISUAL REPRESENTATION
4.Depth perception
–Depth is a result of composing a picture by each eye (from differentangles)
–In a flat TV picture
•Perspective appearance of the subject matter
•Choice of focal length of the camera lens and changes in depth focus
5.Luminance
–RGB can be converted to a luminance (brightness signal) and two colordifference signals (chrominance) for TV signal transmission
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VISUAL REPRESENTATION
6.Temporal Aspects of Illumination
A discrete sequence of still images can be perceived as acontinuous sequence.
The impression of motion is generated by a rapid successionof barely differing still pictures (frames).
Rate must be high enough to ensure smooth transition.
Rate must be high enough so that the continuity of perception isnot disrupted by the dark intervals between pictures
The light is cut off, briefly, between these frames.
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VISUAL REPRESENTATION
7.Continuity of Motion
Continuity is perceived with at least 15 frames per second.
To make motion appear smooth in a recorded film (notsynthetically generated), a rate of 30 frames per second isneeded.
Films recorded with 24 frames per second look strange when largeobjects close to the viewer move quickly.
NTSC (National Television Systems Committee) Standard
Original: 30 frames/second
Currently: 29.97 frames/second
PAL (Phase Alternating Line) Standard
25 frames per second
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VISUAL REPRESENTATION
8.Flicker
If the refresh rate is low, a periodic fluctuation of the perceivedbrightness can result.
Minimum to avoid flicker is 50 Hz.
Technical measures in movies and TV have allowed lowerrefresh rates.
The Refresh rate is the number of times a display's image isrepainted or refreshed per second. A refresh rate of 75 Hz meansthe image is refreshed 75 times in one second.
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SIGNAL FORMATS
RGB
YUV
YIQ
Composite Signals
Instead of sending each component on one channel, send themall
Computer Video Formats
Current video digitization hardware differ in
Resolution of digital images (frames)
Quantization
Frame rate
Motion depends on the display hardware (Figure 5-4 page 86)
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SIGNAL FORMATS
Computer Video Formats
Color Graphics Adapter (CGA)
Resolution: 320 x 200
2 bits / pixel
Enhanced Graphics Adapter (EGA)
Resolution: 640 x 350
4 bits / pixel
Video Graphics Array (VGA)
Resolution: 640 x 480
8 bits / pixel
Super Video Graphics Array (SVGA)
Resolution: 1024 x 768, 1280 x 1024, 1600 x 1280
8 bits / pixel
Video accelerators are needed to avoid reduced performance at higherresolutions
Check the storage requirements of the above systems!
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ANALOG VIDEO
Each frame of video is represented by a fluctuating voltage known as ananalog wave form.
A composite signal has brightness, colour and synchronisation elementscombined in the one signal.
NTSC, PAL and SECAM are the three most widely used composite videosignals.
Analog to Digital Video
NTSC, PAL and SEACAM signals are analog (wave based).
Computers store video in a digital format.
The process of digitizing video is known as capturing or sampling.
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TELEVISION SYSTEMS
Conventional Systems
NTSC : National Television System Committee
Originated in the US
Uses color carriers of approx. 4.429 MHz or approx. 3.57MHz.
With suppressed color carrier, it uses quadrature amplitudemodulation
Refresh rate: 30Hz
# horizontal lines: 525
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TELEVISION SYSTEMS
Conventional Systems
SECAM (stands for Système Electronique Couleur AvecMémoire, the third major broadcast TV standard)
France and Eastern Europe
With suppressed color carrier, it uses frequency modulation
Refresh rate: 25Hz
# horizontal lines: 625
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TELEVISION SYSTEMS
Conventional Systems
PAL : Stands for Phase Alternating Line
a TV standard widely used in Western Europe, China, India,and many other parts of the world.
Uses color carriers of approx. 4.43 MHz
With suppressed color carrier, it uses quadrature amplitudemodulation
Refresh rate: 25Hz
# horizontal lines: 525
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• Table below gives a comparison of the three major analogbroadcast TV systems.
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TV System
FrameRate(fps)
# ofScanLines
TotalChannelWidth(MHz)
BandwidthAllocation (MHz)
Y
I or U
Q or V
NTSC
29.97
525
6.0
4.2
1.6
0.6
PAL
25
625
8.0
5.5
1.8
1.8
SECAM
25
625
8.0
6.0
2.0
2.0
DIGITAL VIDEO
The advantages of digital representation for video are many. Forexample:
Video can be stored on digital devices or in memory, ready to beprocessed (noise removal, cut and paste, etc.), and integrated tovarious multimedia applications;
Direct access is possible, which makes nonlinear video editingachievable as a simple, rather than a complex, task;
Repeated recording does not degrade image quality;
Ease of encryption and better tolerance to channel noise
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TELEVISION SYSTEMS
High-Definition TV (HDTV)
Research began in Japan, 1968
Third Technological Shift (after black and white andcolor TV)
The goal was to “integrate” the viewer with the eventshappening on the screen
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TELEVISION SYSTEMS
High-Definition TV (HDTV)
Resolution
More than 1000 scanning lines
Approximately double the resolution of conventional TV
Higher video bandwidth
About five times that of conventional TV
Resolutions Recommended
High 1440 Level: 1440 x 1152
High Level: 1920 x 1152
Later, 2k x 2k pixels
Frame Rate
No agreement on a fixed frame rate worldwide
50 or 60 frames per second
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TELEVISION SYSTEMS
High-Definition TV (HDTV)
Aspect Ratio
Originally 16:9
Currently 4:3
Interlaced and/or progressive scanning formats
Conventional systems supported interlaced scanning formats
HDTV supports both.
Viewing Conditions
Screen area should be bigger than 8000cm2 for “real” scenes
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DIGITIZATION OF VIDEO SIGNALS
Goes through Sampling, Quantization and Coding.
Just like audio
Composite Coding
Sample the entire analog signal
Simple but has many drawbacks
Depends on the TV standard used
Since luminance information is more important than chrominanceinformation, it takes more bandwidth.
Component Coding
Based on the separate digitization of the components
Luminance (Y) is sampled at 13.5 MHz whereas chrominancecomponents (U and V) are sampled at 6.75 MHz.
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DIGITAL TELEVISION
DVB (Digital Video Broadcasting) started in Europe in the early 90s afterconsiderable progress in video compression techniques
More precisely DTVB (Digital TeleVision Broadcasting)
MPEG-2 for source coding of audio/video data
Satellite Connections, CATV networks and (S)MATV (Small) MasterAntenna TV systems were suitable for digital TV distribution
DVB-S (Satellite) and DVB-C (Cable) were adopted by the EuropeanTelecommunications Standards Institute ETSI as official standards.
Multichannel Microwave Distribution Systems (MMDS) are anotherpossibility.
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DIGITAL TELEVISION
Advantages
Increased number of programs can be transmitted over a TVchannel
Adaptable video/audio quality to each application
Exceptionally secure encryption systems for pay-per-view
Additional services (video on demand, data broadcast,...)
Computers and TV convergence
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