Chapter 3

Fundamental Concepts in Video

3.1 Types of Video Signals

3.2 Analog Video
3.3 Digital Video

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3.1 TYPES OF VIDEO SIGNALS 2
Fundamentals of Multimedia, Chapter 5

Types of Video Signals

Video standards for managing analog output:

A. Component Video

B. Composite video

C. S-Video

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Fundamentals of Multimedia, Chapter 5

A. Component video - 3 Signals

• Higher-end video systems make use of three separate video
signals for the red, green, and blue image planes. Each color
channel is sent as a separate video signal.
• Most computer systems use Component Video, with separate
signals for R, G, and B signals.

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Fundamentals of Multimedia, Chapter 5

A. Component video - 3 Signals

• For any color separation scheme, Component Video gives the
best color reproduction since there is no “crosstalk” between
the three channels. This is not the case for S-Video or
Composite Video, discussed next.

• Component video, however, requires more bandwidth and

good synchronization of the three components.

• component-video cables do not carry audio and are often

paired with audio cables.

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Fundamentals of Multimedia, Chapter 5

B. Composite Video - 1 Signal

• Composite video: color (“chrominance”) and intensity
(“luminance”) signals are mixed into a single carrier wave.

• In video, luminance (luma or Y for short) represents the

brightness in an image (the "black-and-white" of the image).

• While chrominance (chroma or C for short) is the signal used

in video systems to convey the color information of the
picture, separately from the accompanying luma signal

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Fundamentals of Multimedia, Chapter 5

B. Composite Video - 1 Signal

• Since color and intensity are wrapped into the same signal,
some interference between the luminance and chrominance
signals is inevitable.

• All the signals are mixed together and carried on a single

cable as a composite of the three color channels and the
sync signal  Lowest quality for a video signal & less-
precise color definition.

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Fundamentals of Multimedia, Chapter 5

C. S-Video - 2 Signals
S-Video: as a compromise, (separated video, or Super-video)
uses two wires, one for luminance and another for a composite
chrominance signal.
• As a result, there is less crosstalk between the color
information and the crucial gray-scale information
• Compared to a Composite video connection S-Video simply
carries more information to the TV thus producing a slightly
better picture than composite.

• Because an S-video cable only carries the video signal you still
need the old stand (red/white) audio cables in order to hear
sound. 8
Fundamentals of Multimedia, Chapter 5

C. S-Video - 2 Signals

Luminance Y

Ground Y
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3.2 ANALOG VIDEO 10
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Analog Video

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Analog Video
• Analog video is represented as a continuous (time varying)
signal. (Resolution measured in the number of horizontal
scan lines (due to the nature of early cathode-tube
cameras)
• Each line in the video image represents continuous
measurements of the color and brightness along the
horizontal axis.

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Analog Video
• At the end of each line, there is a portion of the waveform
(horizontal blanking interval) that tells the scanning circuit in
the display to retrace to the left edge of the display and then
start scanning the next line.
• Starting at the top, all of the lines on the display are scanned
in this way. One complete set of lines makes a picture. This is
called a frame.
• Once the first complete picture is scanned, there is another
portion of the waveform (vertical blanking interval) that tells
the scanning circuit to retrace to the top of the display and
start scanning the next frame, or picture.
• This sequence is repeated at a fast enough rate so that the 13
displayed images are perceived to have continuous motion.
Fundamentals of Multimedia, Chapter 5

Analog Video

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Analog Video Scanning Systems

• These are two different types of scanning systems. They differ
in the technique used to "paint" the picture on the screen.

• Television signals and compatible displays are typically

interlaced, and computer signals and compatible displays are
typically progressive (non-interlaced).

• These two formats are incompatible with each other; one

would need to be converted to the other before any common
processing could be done.

You have probably heard of the resolution standards 480i, 480p, 720p, 1080i and 1080p. The
15
“i” and “p” after the number actually stands for “interlaced” and “progressive” respectively,
Fundamentals of Multimedia, Chapter 5

A. Progressive Scanning
• A progressive, or non-interlaced, picture is painted on the
screen by scanning all of the horizontal lines of the picture in
one pass from the top to the bottom.

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B. Interlaced Scanning
• In TV, and in some monitors and multimedia standards as well,
another system, called “interlaced” scanning is used.
• Interlaced scanning is where each picture, referred to as a
frame, is divided into two separate sub-pictures, referred to as
fields. Two fields make up a frame.

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B. Interlaced Scanning
• An interlaced picture is painted on the screen in two passes,
by:
• First scanning the horizontal lines of the first field and then
• Retracing to the top of the screen and then
• Scanning the horizontal lines for the second field in-between the
first set.

• In fact, the odd lines (starting from 1) end up at the middle of

a line at the end of the odd field, and the even scan starts at a
half-way point.

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B. Interlaced Scanning

Fig. 3.1: Interlaced raster scan

• Figure 3.1 shows the scheme used. First the solid (odd) lines are
traced, P to Q, then R to S, etc., ending at T; then the even field
starts at U and ends at V.
• The jump from Q to R, etc. in Figure 3.1 is called the horizontal
retrace, during which the electronic beam in the CRT is blanked. The 19
jump from T to U or V to P is called the vertical retrace.
Fundamentals of Multimedia, Chapter 5

B. Interlaced Scanning

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Interlaced & Progressive examples

The animated picture shows the

difference between interlaced and
progressive
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Difference between Interlaced Scan and Progressive Scan?

Fundamentals of Multimedia, Chapter 5

Advantages of Interlaced Scanning

Popularity
• Interlaced scan was the most popular format in which
broadcasters output their TV signals. This is due to the
reduced bandwidth that interlaced scanning requires.
Lower prices
• The internal workings of televisions or other display units
using the interlaced scan method of image rendering are far
less complex than progressive scan devices, meaning that
prices for interlaced units are generally much lower than
progressive scan units

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Disadvantages of Interlaced Scanning

Image artefacts
• During high-motion videos, images rendered by interlaced
devices are prone to distracting image artefacts. This is
because each frame of interlaced video is composed of two
segments that are captured at different moments in time. If
the recorded object – for example, a fast moving sports
sequence, is moving fast enough to be in different positions
when each individual segment is captured, a “motion
artefact” will result.
1. Blurring
• To counter the problem of image artefacts, images produced
on interlaced scan systems are sometimes intentionally 23
blurred, thus producing an image of lesser quality.
Fundamentals of Multimedia, Chapter 5

Disadvantages of Interlaced Scanning

2. Flickering
• On larger screens particularly, an irritating flickering effect can
sometimes become apparent. This flickering is also called
“interline twitter” and is caused by the image on the screen
containing vertical detail that approaches the horizontal
resolution of the video format. Whenever you have seen a TV
presenter’s striped shirt or suit flickering on a screen, this is
interline twitter in action!

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Interlacing problems (Blurring )

Figure 1: TECHSPEC® Man's High-
Speed Movement Using a Progressive
Scanning Sensor

Figure 2: Ghosting and Blurring of

TECHSPEC® Man's High-Speed
Movement Using an Interlaced
Scanning Sensor

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Fundamentals of Multimedia, Chapter 5

Interlacing problems (Flickrring)

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De-interlacing
• Deinterlacing is the process of converting interlaced video,
such as common analog television signals or 1080i
format HDTV signals, into a non-interlaced form.
• The simplest de-interlacing method consists of discarding one
field and duplicating the scan lines of the other field. The
information in one field is lost completely using this simple
technique.

Take the picture as an

example, with four different
fields numbered 1 to 4:

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How to Deinterlace Footage

Fundamentals of Multimedia, Chapter 5

De-interlacing
The fields have
been separated.

Demonstrating how the top field (fields 1 and 3) is on

even numbered lines, while the bottom field (fields 2,4)
is on odd numbered lines.

You'll notice
that the height
has been cut
in half and
Dante looks
28
too short (or
too wide).
Fundamentals of Multimedia, Chapter 5

Advantages of Progressive Scanning

No image artefacts
• None of the image artefacts associated with interlaced images
are apparent in systems using progressive scan technology,
because the lines on the screen are displayed sequentially, not
at two different times.

No blurring
• As a result of the lack of image artefacts, no intentional
blurring is necessary in progressive scan systems.

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Disadvantages of Progressive Scanning

Higher quality images
• Images are smoother are more detailed in progressive scan as
they are refreshed at a faster frequency.

Higher bandwidth means lack of use

• As an image using a progressive scan requires a higher
bandwidth than an interlaced image of the same size,
broadcasters using analogue signals hardly ever use
progressive scan images.

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Analog Video Broadcast Standards

• Broadcast standards, are ways of encoding video information
for broadcast to television receivers. These standards are also
used to describe the display capabilities of video monitors and
are thus also called video output formats (VOFs).

• They are encoding or formatting standards for the

transmission and reception of television signals.

• There are three main analog television systems in use around

the world:
• NTSC: in USA but replaced with ATSC Digital Television
Standard
• PAL, and SECAM: In Europe 31
Fundamentals of Multimedia, Chapter 5

A. NTSC
NTSC: National Television Standards Committee:
• United States, Canada, Mexico, Japan
• Defined a method for encoding information into the
electronic signal that ultimately created a television
picture.
• A single frame of video  525 horizontal scan lines
• NTSC follows the interlaced scanning system, and each frame is
divided into two fields, with 262.5 lines/field.

• Higher Frame Rate - Use of 30 frames per second (really

29.97) reduces visible flicker.
• Thus the horizontal sweep frequency is 525×29.97 ≈ 15, 734
lines/sec, so that each line is swept out in (1/15734) × 10 6 sec 32
≈ 60 μsec.
Fundamentals of Multimedia, Chapter 5

A. NTSC
• Fig. 3.4 shows the effect of “vertical retrace & sync” and
“horizontal retrace & sync” on the NTSC video raster.

33
Fig. 3.4: Video raster, including retrace and sync data
Fundamentals of Multimedia, Chapter 5

A. NTSC
• Vertical retrace takes place during 20 lines reserved for
control information at the beginning of each field. Hence, the
number of active video lines per frame is only 485.
• Similarly, almost 1/6 of the raster at the left side is blanked for
horizontal retrace and sync. The non-blanking pixels are called
active pixels.
• Since the horizontal retrace takes 10.9 μsec, this leaves 52.7 μsec
for the active line signal during which image data is displayed.
• NTSC TV is only capable of showing about 70% of the specified
active lines.

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B. PAL
PAL: Phase Alternate Line
• United Kingdom, Western Europe, Australia, South Africa,
China, and South America.
• Screen resolution: 625 horizontal lines  more picture detail.
• Interlaced, each frame is divided into 2 fields, 312.5 lines/field
• Scan rate to 25 fps  More Flicker - Due to the lower frame
rate
• Field: 1/50 of a second to draw (50 Hz).

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C. SECAM

SECAM: Sequential Color and Memory

• France, Eastern Europe, the former USSR.
• Similar to PAL:
• SECAM is a 625-line, 50 Hz system.
• SECAM shares with PAL/625, the higher number of scan lines
than NTSC/525.
• Scan rate to 25 fps  More Flicker - Due to the lower frame rate

• They differ slightly in their color coding scheme

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Color TV Systems of the world

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• Table 3.2 gives a comparison of the three major analog

broadcast TV systems.

• Table 3.2: Comparison of Analog Broadcast TV Systems

Total Bandwidth
Frame # of
TV System Rate Scan
• Channel Allocation (MHz)
Width
(fps) Lines Y I or U Q or V
(MHz)
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
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•
3.3 DIGITAL VIDEO 39
Fundamentals of Multimedia, Chapter 5

Digital Video
Digital video is a type of digital recording system that works by
using a digital rather than an analog video signal.

The advantages of digital representation for video are many. For

example:
1. Video can be stored on digital devices or in memory, ready to
be processed (noise removal, cut and paste, etc.), and
integrated to various multimedia applications;
2. Direct random access is possible, which makes nonlinear video
editing achievable as a simple, rather than a complex, task;
3. Repeated recording does not degrade image quality;
4. Ease of encryption and better tolerance to channel noise 
Almost all digital video uses component video
5. No need for blanking and sync pulse 40
Fundamentals of Multimedia, Chapter 5

Video color models - Y color spaces

• Y is luminance, Such as : YIQ, YUV, YCbCr…

• Used in television sets and videos, I or U and Q or V is
chromaticity

IT342
• Black & White television sets display only Y.
• color TV sets convert to RGB, YUV=PAL, YIQ=NTSC.

• Can be used as well before image compression where

High bandwidth for Y and Small bandwidth for
chromaticity. 41
Fundamentals of Multimedia, Chapter 5

YCbCr color space

• YCbCr is a color space for digital television systems.

• YCbCr Color Space is used in MPEG video compression

standards: Y is luminance, Cb is blue chromaticity, Cr is

IT342
red chromaticity.

• Chroma Cb corresponds to the U color component, and

chroma Cr corresponds to the V component of a general
YUV color space.

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Chroma Subsampling
• it is the practice of encoding images by implementing less
resolution for chroma information than for luma information,
taking advantage of the human visual system's lower acuity
for color differences than for luminance.

• Since humans see color with much less spatial resolution than
they see black and white, it makes sense to “decimate” the
chrominance signal.

• Interesting (but not necessarily informative!) names have

arisen to label the different schemes used.
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Chroma Subsampling
• To begin with, numbers are given stating
how many pixel values, per four original
pixels, are actually sent:
• The chroma subsampling scheme “4:4:4”
indicates that no chroma subsampling is
used: each pixel’s Y, Cb and Cr values are
transmitted, 4 for each of Y, Cb, Cr.

• The scheme “4:2:2” indicates horizontal

subsampling of the Cb, Cr signals by a
factor of 2. That is, of four pixels
horizontally labelled as 0 to 3, all four Ys
are sent, and every two Cb’s and two Cr’s
are sent, as (Cb0, Y0)(Cr0, Y1)(Cb2,
Y2)(Cr2, Y3)(Cb4, Y4), and so on (or 44
averaging is used).
Fundamentals of Multimedia, Chapter 5

Chroma Subsampling
• The scheme “4:1:1” subsamples
horizontally by a factor of 4.

• The scheme “4:2:0” subsamples in both

the horizontal and vertical dimensions by
a factor of 2. Theoretically, an average
chroma pixel is positioned between the
rows and columns as shown Fig.3.6.
• Scheme 4:2:0 along with other schemes
is commonly used in JPEG and MPEG 45
(see later chapters in Part 2).
Fundamentals of Multimedia, Chapter 5

Chroma Subsampling

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Types of Digital Displays

• DTV - Digital television encompasses all of the underlying
standards for SDTV, EDTV and HDTV developed by the
ATSC.

• A TV described as being DTV-ready, will be able to display

the new digital broadcasts and will use one of the three
standards listed below:
• SDTV (Standard Definition TV): the NTSC TV or higher.
• EDTV (Enhanced Definition TV): 480 active lines or higher.
• HDTV (High Definition TV): 720 active lines or higher.

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Differences
Fundamentals of Multimedia, Chapter 5

Types of Digital Displays

Standard-Definition TV:
• SDTV is the digital broadcast television standard defined
under the DTV standards developed by the ATSC.
• An SDTV is defined as being able to receive an ATSC
signal and in most cases will have 480 lines of resolution.
• aspect ratio of 4:3.
• An SDTV will be the basic television compatible with the
new standards.

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Types of Digital Displays

Enhanced-Definition TV:
• EDTV, like SDTV, displays 480 lines.
• However, instead of being interlaced, it is
a progressive scan image.
• This results in a smoother image, especially during action
sequences, as well as a brighter picture.
• Nearly all ED televisions have an aspect ratio of 16:9.
• Just a note, most EDTV displays are plasma panels.
Although, most plasma screens are HDTVs.

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Types of Digital Displays

High-Definition TV:
• HDTV comes in three flavors, 720p, 1080i and now 1080p;
really there are 18 DTV formats, but most TVs will use one of
these three.
• The first resolution displays 720 lines progressively while the
second displays 1,080 lines interlaced.
• 1080p should also be fully backward compatible for 720p and
1080i TVs.
• Nearly all HD televisions have an aspect ratio of 16:9.

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• The standard supports video scanning formats shown in Table

3.4. In the table, “I” mean interlaced scan and “P” means
progressive (non-interlaced) scan.

• Table 3.4: Advanced Digital TV formats supported by ATSC

# of Active # of Active Aspect Ratio Picture Rate
Pixels per line Lines
1,920 1,080 16:9 60I 30P 24P
1,280 720 16:9 60P 30P 24P
•
704 480 16:9 & 4:3 60I 60P 30P 24P
640 480 4:3 60I 60P 30P 24P
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• The salient difference between conventional TV and

HDTV:
• HDTV has a much wider aspect ratio of 16:9 instead of
4:3.
• HDTV moves toward progressive (non-interlaced) scan.
The rationale is that interlacing introduces serrated
edges to moving objects and flickers along horizontal
edges.

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Comparison

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