Multimedia fundamental concepts in video

‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬

Fundamental Concepts
in Video
BY
RAFIDH

 Types of Video Signals
1- Component video
2- Composite Video
3- S-Video
 Analog Video
 Digital Video
 Further Exploration
3
Overview
•Types of Video Signals
1- Component video
2- Composite Video
3- S-Video
•Analog Video
•Digital Video
•Further Exploration

Video Display Interfaces
 These Interfaces are builled for video signal
transmission from some output devices (e.g., set-top
box, video player, video card, and etc.) to a video
display (e.g., TV, monitor, projector, etc.).
 There have been a wide range of video display
interfaces, supporting video signals of different
formats (analog or digital, interlaced or progressive),
different frame rates, and different resolutions, these
interfaces are:
 Analog interfaces: including Component Video, Composite Video,
and S-Video,
 Digital interfaces: including DVI, HDMI, and DisplayPort.
4

5
Component video
Higher-end video systems make use of three
separate video signals for the red, green, and blue
image planes.
 This kind of system has three wires (and
connectors) connecting the camera or other devices
to a TV or monitor.
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.
 For any color separation scheme, Component
Video gives the best color reproduction since there
is no “crosstalk” between the three channels.

6
•Component video, however, requires more bandwidth
and good synchronization of the three components.
•.

7
Composite video
In Composite video: color (“chrominance”)
and intensity (“luminance”) signals are mixed
into a single carrier wave.
 Chrominance is a composition of two color
components (I and Q, or U and V).
 In NTSC TV, e.g., I and Q are combined into a
chroma signal, and a color subcarrier is then
puts the chroma signal at the high-frequency
end of the channel shared with the luminance
signal.

8
Composite Video
The chrominance and luminance components
can be separated at the receiver end and then the
two color components can be further recovered.
 When connecting to TVs or VCRs, Composite
Video uses only one wire and video color signals
are mixed, not sent separately.
The audio signal is another addition to this one
signal.
 Since color information is mixed and both color
and intensity are wrapped into the same signal,
some interference between the luminance and
chrominance signals is inevitable.

10
S-Video
S-video :( Separated video, or Super-video,
e.g., in S-VHS) 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.
The reason for placing luminance into its own
part of the signal is that black-and-white
information is most crucial for visual perception
S-Video: as a compromise, (separated video,.

11
In fact, humans are able to differentiate spatial
resolution in grayscale images with a much
higher acuity than for the color part of color
images.
Therefore color information sent can be much
less accurate color information than intensity
information — we can only see fairly large blobs
of color, so it makes sense to send less color
detail.
S-Video

14
Digital Display Interfaces
Given the rise of digital video processing and the monitors
that directly accept digital video signals, there is a great
demand toward video display interfaces that transmit
digital video signals
Today, the most widely used digital video interfaces
include Digital Visual Interface (DVI), High- Definition
Multimedia Interface (HDMI), and DisplayPort, as shown
in Fig. () .
Figure () :Connectors of different digital display interfaces.
From left to right: DVI, HDMI, DisplayPort.

15
Digital Visual Interface (DVI)
Digital Visual Interface (DVI) is a video display interface
developed by the Digital Display Working Group (DDWG).
The digital interface is used to connect a video source,
such as a video display controller to a display device,
such as a computer monitor. It was developed with the
intention of creating an industry standard for the transfer
of digital video content.
The interface is designed to transmit uncompressed
digital video and can be configured to support multiple
modes such as DVI-A (analog only), DVI-D (digital only) or
DVI-I (digital and analog). Featuring support for analog
connections, the DVI specification is compatible with the
VGA interface

16
High-Definition Multimedia Interface (HDMI)
is the link which is not preferred length of
the cable used to transmit audio and video
so that the video be in uncompressed and
the sound is compressed or uncompressed
in a single cable and is newly transferred
online via cable also has cable is designed to
be a replacement for cables analog (analog)
and cable work by protocol or Technique
called( TMDS) cable also designed to be
compatible with the DVI cable without any
loss of signal or image quality.

17
DisplayPort
DisplayPort is a digital display interface developed by
VESA, starting from 2006. It is the first display
interface that uses packetized data transmission, like
the Internet or Ethernet. DisplayPort can be used to
transmit audio and video simultaneously, or either of
them.
Specifically, it is based on small data packets known
as
micro packets, which can embed the clock signal
within the data stream.
DisplayPort can achieve a higher resolution yet with
fewer pins than the previous technologies. The use of
data packets also allows DisplayPort to be extensible,
i.e., new features can be added over time without
significant changes to the physical interface itself.

18
 The video signal path can have 6–16 bits per color
channel, and the audio path can have up to eight
channels of 24-bit 192kHz uncompressed PCM audio or
carry compressed audio.
 Compared with HDMI, DisplayPort has slightly more
bandwidth, which also accommodates multiple
streams of audio and video to separate devices.
 the VESA specification is royalty-free, while HDMI
charges an annual fee to manufacturers. These points
make DisplayPort a strong competitor to HDMI in the
consumer electronics market, as well.

19
Analog Video
A picture is "drawn" on a television or computer display screen
by sweeping an electrical signal horizontally across the display
one line at a time. The amplitude of this signal versus time
represents the instantaneous brightness at that physical point on
the display.
Analog video is represented as a continuous (time-varying)
signal. An analog signal f(t) samples a time-varying image. So-
called “progressive” scanning traces through a complete picture
(a frame) row-wise for each time interval.
A high-resolution computer monitor typically uses a time
interval of 1/72 s.


20
Analog Video
In TV, and in some monitors and multimedia standards as well, another
system, called “interlaced” scanning is used.
1- The odd-numbered lines are traced first, and then the even-numbered
lines are traced. This results in “odd” and “even” fields — two fields
make up one frame.
2- 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.
Fig. 5.1: Interlaced raster scan

21
3- Figure 5.1 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.
4- The jump from Q to R, etc. in Figure 5.1 is called
the horizontal retrace, during which the electronic
beam in the CRT is blanked. The jump from T to U
or V to P is called the vertical retrace.
Analog Video

22
Interlacing was invented because, when
standards were being defined, it was difficult to
transmit the amount of information in a full frame
quickly enough to avoid flicker. The double
number of fields presented to the eye reduces
perceived flicker.
Because of interlacing, the odd and even lines
are displaced in time from each other — generally
not noticeable except when very fast action is
taking place on screen, when blurring may occur.
 For example, in the video in Fig. 5.2, the moving
helicopter is blurred more than is the still
background.
Analog Video

23
Fig. 5.2: Interlaced scan produces two fields for each frame. (a) The
video frame, (b) Field 1, (c) Field 2, (d) Difference of Fields
(a)
(b)
(c)
(d)

24
• Since it is sometimes necessary to change the frame
rate, resize, or even produce stills from an interlaced
source video, various schemes are used to “de-
interlace” it.
a) 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 .
b) Other more complicated methods that retain
information from both fields .
CRT (Cathode Ray Tube) displays are built like
fluorescent lights and must flash 50–70 times per
second to appear smooth.
The jump from Q to R and so on in Fig. 5.1 is called the
horizontal retrace, during which the electronic beam in
the CRT is blanked. The jump from T to U or V to P is
called the vertical retrace.

25
Since voltage is one-dimensional—it is simply a signal that
varies with time—how do we know when a new video line
begins? That is, what part of an electrical signal tells us that
we have to restart at the left side of the screen?
Analog video use a small voltage offset from zero to
indicate “black”, and another value such as zero to indicate
the start of a line
Fig. 5.3 Electronic signal for one NTSC scan line

26
• Figure 5.3 shows a typical electronic signal for one
scan line of NTSC composite video. ‘White’ has a
peak value of 0.714V; ‘Black’ is slightly above zero at
0.055V; whereas Blank is at zero volts.
• The vertical retrace and sync ideas are similar to the
horizontal one, except that they happen only once per
field, see the following figure.

27
Figure (): Composite video, The NTSC video signal consists of
30 frames per second, with each frame containing 480 to 486
lines of video. Each frame is broken into two fields, one
containing the odd lines and the other containing the even
lines. Each field starts with a group of vertical sync pulses,
followed by successive lines of video information separated by
horizontal sync pulses.

28
NTSC (National Television System Committee)
 TV standard is mostly used in North America
and Japan.
 It uses the familiar 4:3 aspect ratio.
uses 525 scan lines per frame
30 frames per second (fps).(more exactly 29.07
fps)
NTSC follows the interlaced scanning system

29
NTSC video is an analog signal with no fixed
horizontal resolution. Therefore one must
decide how many times to sample the signal for
display: each sample corresponds to one pixel
output.
 A “pixel clock” is used to divide each
horizontal line of video into samples. The
higher the frequency of the” pixel clock, the
more samples per line

30
Fig. 5.4: Video raster, including retrace and sync data

31
Different video formats provide different
numbers of samples per line, as listed in Table
5.1.
Table 5.1: Samples per line for various video formats

32
 NTSC uses the YIQ color model, and the technique
of quadrature modulation to combine (the spectrally
overlapped part of) I (in-phase) and Q (quadrature)
signals into a single chroma signal C :
C = I cos(Fsct) + Q sin(Fsct) (5.1)
 The NTSC composite signal is a further
composition of the luminance signal Y and the
chroma signal as defined below:
composite = Y +C = Y +Icos(Fsct) + Qsin(Fsct)
(5.2)

33
Fig. 5.5: Interleaving Y and C signals in the NTSC spectrum

34
The first step in decoding the composite signal at
the receiver side is the separation of Y and C.
• After the separation of Y using a low-pass filter, the
chroma signal C can be demodulated to extract the
components I and Q separately. To extract I :
1. 1- Multiply the signal C by 2 cos(Fsct), i.e.,
2
·2cos( ) ·2cos ( ) ·2sin( )cos( )
·(1 cos(2 )) ·2sin( )cos( )
·cos(2 ) ·sin(2 )
sc sc sc sc
sc sc sc
sc sc
C F t I F t Q F t F t
I F t Q F t F t
I I F t Q F t
 
  
  

35
1. 2. Apply a low-pass filter to obtain I and
discard the two higher frequency (2Fsc)
terms.
 Similarly, Q can be extracted by first
multiplying C by 2sin(Fsct) and then low-
pass filtering.

36
PAL (Phase Alternating Line) is a TV standard
widely used in Western Europe, China, India,
and many other parts of the world.
 PAL uses 625 scan lines per frame, at 25
frames/second, with a 4:3 aspect ratio and
interlaced fields.
 It uses an 8 MHz channel and allocates a
bandwidth of 5.5 MHz to Y, and 1.8 MHz each to
U and V. The color subcarrier frequency is fsc ≈
4.43 MHz.
PAL VIDEO

37
To improve picture quality, chroma signals
have alternate signs (e.g., +U and -U) in
successive scan lines, hence the name “Phase
Alternating Line”.
This facilitates the use of a (line rate) comb
filter at the receiver — the signals in
consecutive lines are averaged so as to cancel
the chroma signals (that always carry opposite
signs) for separating Y and C and obtaining
high quality Y signals.
PAL VIDEO

38
 SECAM stands for Système Electronique Couleur
Avec Mémoire, the third major broadcast TV
standard.
 SECAM also uses 625 scan lines per frame, at 25
frames per second, with a 4:3 aspect ratio and
interlaced fields.
 SECAM and PAL are very similar. They differ
slightly in their color coding scheme:
 In SECAM, U and V signals are modulated
using separate color subcarriers at 4.25 MHz
and 4.41 MHz respectively.
(b) They are sent in alternate lines, i.e., only one
SECAM Video

39
Table 5.2 gives a comparison of the three major
analog broadcast TV systems.
Table 5.2: Comparison of Analog Broadcast TV
Systems

40
The advantages of digital representation for
video are many. It permits:
 storing Video on digital devices or in memory,
ready to be processed (noise removal, cut and
paste, etc.), and integrated to various multimedia
applications .
 Direct access is possible, which makes
nonlinear video editing .
 Repeated recording does not degrade image
quality .
Ease of encryption and better tolerance to
channel noise.
Digital Video

41
Since humans see color with much less spatial
resolution than they see black and white, it makes sense
to “decimate” the chrominance signal.
Video signals is separated into a lightness or “luma”
component and two color or “chroma” components,
similar to how images can be separated into three red,
green and blue (RGB) components.
 The luma and chroma components would then be
referred to as YUV (with analog) or YCbCr (with digital) as
opposed to RGB.
Once separated, the chroma resolution would then be
reduced by half or more through a process called
“chroma subsampling
-Chroma Subsampling

42
The end result is a video signal that appears more
detailed at the same broadcast bandwidth, since the
luma component occupies a greater fraction of the video
signal
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.

43
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.5.6.
Scheme 4:2:0 along with other schemes is
commonly used in JPEG and MPEG (see later
chapters in Part 2).

44
Fig. 5.6: Chroma subsampling

45
(No Color Reduction)
(1/2 the Luma Samples)
Horizontally subsampling
Horizontally subsampling
horizontally and vertically
Same
bit rate
and
same
sample
s no.

46
CCIR is the Consultative Committee for International
Radio, and one of the most important standards it has
produced is CCIR-601, for component digital video.
– This standard has since become standard ITU-R-601,
an international standard for professional video
applications
The NTSC version has 525 scan lines, each having 858
pixels (with 720 of them visible, not in the blanking
period). Because the NTSC version uses 4:2:2, each pixel
can be represented with two bytes (8 bits for Y and 8 bits
alternating between Cb and Cr).
Find data rate in Mbps (megabits per second)
- CCIR Standards for Digital Video

47
CIF stands for Common Intermediate Format
specified by the CCITT (International Telegraph
and Telephone Consultative Committee).
(a)The idea of CIF is to specify a format for
lower bitrate.
(b) CIF is about the same as VHS quality. It
uses a progressive (non-interlaced) scan.
(c) Note, CIF is a compromise of NTSC and
PAL in that it adopts the ‘NTSC frame rate and
half of the number of active lines as in PAL.

48
 The main thrust of HDTV (High Definition TV) is
not to increase the “definition” in each unit area,
but rather to increase the visual field especially
in its width.
 The first generation of HDTV was based on
an analog technology developed by Sony and
NHK in Japan in the late 1970s.
 MUSE (MUltiple sub-Nyquist Sampling
Encoding) was an improved NHK HDTV with
hybrid analog/digital technologies that was
put in use in the 1990s. It has 1,125 scan lines,
interlaced (60 fields per second), and 16:9
aspect ratio
- HDTV (High Definition TV)

49
Since uncompressed HDTV will easily
demand more than 20 MHz bandwidth, which
will not fit in the current 6 MHz or 8 MHz
channels, various compression .
 It is also anticipated that high quality HDTV
signals will be transmitted using more than
one channel even after compression.

50
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

Multimedia fundamental concepts in video

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