Chapter Five

Fundamental Concepts of Video

Complied by: Nigusu Y. (nigusu02@gmail.com )

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 Introduction
o Video is an electronic medium for the recording, copying, playing,
broadcasting and displaying of motion visual images.

o Video is a series of images which are displayed on screen at fast speed ( e.g
30 images per second)

o It projects single images at a fast rate producing the illusion of continuous

motion.

o The rate at which the frames are projected is generally between 24 and 30
frames per second (fps).

o The rate at which these images are presented is referred to as the Frame
Rate .

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o A single image is called frame and video is a series of frames.

o An image just like conventional images is modeled as a matrix of pixels.

o To model smooth motion psychophysical studies have shown that a rate of

30 frames a second is good enough to simulate smooth motion.

o Video content is any content format that features or includes videos like

live videos, recorded presentations, movies, webinars or animated GIF.

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 Types of colour video Signals
o Component video
 Each primary is sent as a separate video signal.

 Best color reproduction.

 Requires more bandwidth and good synchronization of the three

components

 Component video takes the different components of the video and

breaks them into separate signals.

 Improvements to component video have led to many video formats,

including S-Video, RGB etc.

 Component cables are designed for HDTV.

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o Composite Video
 Color (chrominance) and luminance signals are mixed into a single carrier
wave.
 Some interference between the two signals is unavoidable.
 Composite analog video has all its components (brightness, color,
synchronization information, etc.) combined into one signal.
 Due to the compositing (or combining) of the video components, the
quality of composite video is marginal at best.
 The results are color bleeding, low clarity and high generational loss.
 Composite cables are designed for older, standard definition (SD)
systems.
 The yellow plug carries the video, while the red and white cables carry the
audio 5
o Separated video
– Compromise between component analog video and the composite video.

– It uses two lines, one for luminance and another for composite
chrominance signal

– The National Television Standards Committee ( NTSC) standard used in

North America and Japanese Television uses a 768 by 484 display.

– The Phase Alternative system (PAL) standard for European television is

slightly larger at 768 by 576.

– Since the resolution between analogue video and computers is different,

conversion of analogue video to digital video at times can be down-sizing
of the video and the loss of some resolution.

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 Types of Videos
o Analog Video
– Analog video is a video signal represented by one or more analog signals

– Analog technology requires information representing images and sound

to be in a real-time continuous scale electric signal between sources and

receivers.

– It is used throughout the television industry.

– For television, images and sound are converted into electric signals by

transducers.

– Distortion of images (loosing the original shape) and noise (colour

fluctuation and boosting images) are common problems for analog video.
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 Con’t
– In an analogue video signal, each frame is represented by a fluctuating

voltage signal known as analogue waveform.

– One of the earliest formats for analog video was composite video.

– Analog formats are vulnerable to loss due to transmission noise effects.

– Quality loss is also possible from one generation to another.

– This type of loss is like photocopying, in which a copy of a copy is

never as good as the original.

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o Digital Video

– Digital video is an electronic representation of moving visual

images (video) in the form of encoded digital data.

– It comprises a series of digital images displayed in rapid succession.

– Computer based digital video is defined as a series of individual

images and associated audio.

– These elements are stored in a format in which both elements (pixel

and sound sample) are represented as a series of binary digits (bits).

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 Con’t
 There are two significant advantages for using computers for digital
video :

o The ability to randomly access the storage of video

o Compress the video stored.

o Advantages:

– Direct random access –> good for nonlinear video editing

– No problem for repeated recording

– No need for blanking and sync pulse

o Almost all digital video uses component video

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 Factors of Digital video
o Frame Rate

 The standard for displaying any type of non-film video is 30 frames

per second (film is 24 frames per second).

 This means that the video is made up of 30 (or 24) pictures or frames

for every second of video.

 Additionally these frames are split in half (odd lines and even lines),

to form what are called fields.

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o Colour Resolution
 Color resolution refers to the number of colors displayed on
the screen at one time.

 Computers deal with color in an RGB (red-green-blue)

format, while video uses a variety of formats.

 One of the most common video formats is called YUV.

 Although there is no direct correlation between RGB and

YUV, they are similar in that they both have varying levels of
color depth (maximum number of colour).

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o Spatial Resolution

– The third factor is spatial resolution or in other words, "How big is the
picture?".

– Since PC and Macintosh computers generally have resolutions in

excess of 640 by 480, most people assume that this resolution is the
video standard.
o Image Quality

– The last, and most important factor is video quality that is acceptable

for your application.

– For some this may be 1/4 screen, 15 frames per second (fps), at 8 bits
per pixel.

– Other require a full screen (768 by 484), full frame rate video, at 24

bits per pixel (16.7 million colours). 13

 Displaying Video
 There are two ways of scanning / displaying video on screen:
 Interlaced scan
 Progressive scan
o Interlaced Scanning
 Interlaced video displays even and odd scan lines as separate fields.

 Interlaced scanning writes every second line of the picture during a

scan, and writes the other half during the next sweep.

 Doing that we only need 25/30 pictures per second.

 This idea of splitting up the image into two parts became known as
interlacing and the splitted up pictures as fields.

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o During the first scan the upper field is written on screen.
o The first, 3rd, 5th, etc. line is written and after writing each line the
electron beam moves to the left again before writing the next line.
o Once all the odd lines have been written the electron beam travels back to
the upper left of the screen and starts writing the even lines.

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 Originally used in traditional analog SD (Standard Definition)

broadcasts since it was more efficient in transmitting video.

 Examples interlaced video displaying

o Television

 Scans 625, 525 horizontal lines top to bottom

 Scan line using interlacing system

 Scan 25-30HZ for fulltime

 Uses limited colour palette and restricted luminance (lightness or

darkness)

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o Progressive Scanning
 Progressive scan video content displays both the even and odd
scan lines (the entire video frame) on the TV at the same time.

 PC CRT displays are fundamentally different from TV screens.

 Monitor writes a whole picture per scan.

 Progressive scan updates all the lines on the screen at the same
time, 60 times every second.

 This is known as progressive scanning and today all PC screens

write a picture like this.

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 Examples progressive video displaying

o Computer

– Scans 480 horizontal lines from

– Scan each line progressively
– Scan full frame at a rate of typically 66.67 HZ or higher
– Use RGB color model
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 Recording Video

o CCDs (Charge Coupled Devices) a chip containing a series of tiny, light-

sensitive photo-sites that forms the heart of all electronic and digital
cameras.

o Digital camera uses lens which focuses the image onto a CCD, which
then converts the image into electrical pulses saved into memory.

o In short, just as the film in a conventional camera records an image

when light hits it, the CCD records the image electronically.

o The photo-sites convert light into electrons.

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 Video Broadcasting Standards/ TV standards
 The video broadcasting standards are: PAL, NTSC, SECAM and HDTV
o PAL (Phase Alternate Line)
 PAL uses 625 horizontal lines at a field rate of 50 fields per second (or 25
frames per second).
 Only 576 of these lines are used for picture information with the remaining
49 lines used for sync or holding additional information such as closed
captioning.

 It is used in Australia, New Zealand, United Kingdom, and Europe.

 Scans 625 lines per frame, 25 frames per second (40 msec/frame)

 Interlaced, each frame is divided into 2 fields, 312.5 lines/field

 For color representation, PAL uses YUV color model

o In PAL,
– 5.5 MHz is allocated to Y,
– 1.8 MHz each to U and V 20
o SECAM (Sequential Color with Memory)

 SECAM uses the same bandwidth as PAL but transmits the color

information sequentially.

 It is used in France, East Europe, etc

 SECAM (System Electronic Pour Couleur Avec Memoire) is very

similar to PAL.

 It specifies the same number of scan lines and frames per second.

 It is the broadcast standard for France, Russia, and parts of Africa and

Eastern Europe.
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o NTSC (National Television Standards Committee)
 NTSC is a black-and-white and color compatible 525-line system that
scans a nominal 30 interlaced television picture frames per second.

 Used in USA, Canada, and Japan.

 525 scan lines per frame, 30 frames per second

 Interlaced, each frame is divided into 2 fields i.e. 262.5 lines/field

 20 lines reserved for control information at the beginning of each field

 So a maximum of 485 lines of visible data

 Each line takes 63.5 microseconds to scan.

 For color representation, NTSC uses YIQ color model.

 Basic Compression Idea

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o HDTV (High Definition Television)
 High-Definition television (HDTV) means broadcast of television signals
with a higher resolution than traditional formats (NTSC, SECAM, PAL)
allow.

 Except for early analog formats in Europe and Japan, HDTV is broadcasted
digitally and its the introduction of digital television (DTV).

 Modern plasma television uses this broadcast

 It consists of 720-1080 lines and higher number of pixels (as many as 1920
pixels).

 Having a choice in between progressive and interlaced is one advantage of

HDTV.

 HDTV signal is digital resulting in crystal clear, noise-free pictures and CD

quality sound. 23
 Color Models in Video
 YUV and YIQ are the two commonly used color models in video.
o YUV Color Model
 Initially, for Phase Alternative system (PAL) analog video, it is now also
used in CCIR 601 standard for digital video

 Chrominance is defined as the difference between a color and a reference

white at the same luminance.

 The YUV color model is the basic color model used in analogue color TV
broadcasting.

 Initially YUV is the re-coding of RGB for transmission efficiency

(minimizing bandwidth) and for downward compatibility with black-and
white television.

 The YUV color space is “derived” from the RGB space.

 It comprises the luminance (Y) and two color difference (U, V) components
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 It can be represented by U and V -- the color differences.
U=B-Y
V=R-Y
– If b/w image, then U = V = 0. --> No chrominance!

 The luminance can be computed as a weighted sum of red, green and blue

components;

 The color difference(chrominance) components are formed by

subtracting luminance from blue and from red.

 The principal advantage of the YUV model in image processing is

decoupling of luminance and color information.

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o The importance of this decoupling is that the luminance component of an image

can be processed without affecting its color component.

o Notice: In the middle it is completely black, which is where U and V are zero,

and Y is as well and if there is no chrominance the picture can be B and W.

o U is the axis from blue to yellow and V is the axis from magenta to cyan.

o Y ranges from 0 to 1 (or 0 to 255 in digital formats), while U and V range from -
0.5 to 0.5 (or -128 to 127 in signed digital form, or 0 to 255 in unsigned form).

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 YIQ Color Model
o The YIQ colour space model is use in U.S. commercial colour television
broadcasting (NTSC).

o It is a rotation of the RGB colour space such that the Y axis contains the
luminance information, allowing backwards-compatibility with black-and-
white colour TV's, which display only this axis of the colour space.

o The chrominance information is contained in the I (orange-blue) and Q (purple-

green) axes, which are roughly orthogonal.

o The human visual system is much more sensitive to changes in the I axis than in
the Q axis, allowing the Q axis to be transmitted with less fidelity, conserving
bandwidth.

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Thanks!

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