2. • outlines
• Types of video
• Analog video
• Digital video
• Types of color video signal
• Video Broadcasting Standards/ TV standards
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3. Analog Video
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. Distortion of images and noise are
common problems for analog video.
In an analogue video signal, each frame is represented by a fluctuating voltage
signal. This is known as an analogue waveform.
One of the earliest formats for this was composite video. Analog formats are
susceptible to loss due to transmission noise effects. 3
4. 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. Most TV is still sent and received as an analog signal.
Once the electrical signal is received, we may assume that brightness is at
least a monotonic function of voltage.
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.
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5. A high-resolution computer monitor typically uses a time interval of 1n2
second. In TV and in some monitors and multimedia standards, another
system, interlaced scanning, is used. Here, the odd-numbered lines are traced
first, then the even-numbered lines. This result in “odd” and “even” fields –
two fields make up one frame.
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6. 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 halfway point. The following figure
shows the scheme used. First the solid (odd) lines are traced – P to Q, then R to
S, and so on, ending at T – then the even field starts at U and ends at V. The scan
lines are not horizontal because a small voltage is applied, moving the electron
beam down over time
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8. Digital Video
Digital technology is based on images represented in the form of bits. A digital
video signal is actually a pattern of 1’s and 0’s that represent the video image.
With a digital video signal, there is no variation in the original signal once it is
captured on to computer disc. Therefore, the image does not lose any of its
original sharpness and clarity. The image is an exact copy of the original. A
computer is the most common form of digital technology. The limitations of
analog video led to the birth of digital video.
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9. Digital video is just a digital representation of the analogue video signal.
Unlike analogue video that degrades in quality from one generation to the
next, digital video does not degrade. Each generation of digital video is
identical to the parent. Even though the data is digital, virtually all digital,
formats are still stored on sequential tapes. There are two significant
advantages for using computers for digital video:
the ability to randomly access the storage of video and
Compress the video stored
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10. 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).
Almost all digital video uses component video.
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, and so on) and integrated into various multimedia
applications
Direct access, which makes nonlinear video editing simple
Repeated recording without degradation of image quality
Ease of encryption and better tolerance to channel noise
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11. Analog vs. Digital Video
An analog video can be very similar to the original video copied, but
it is not identical. Digital copies will always be identical and will
not lose their sharpness and clarity over time. However, digital
video has the limitation of the amount of RAM available, whereas
this is not a factor with analog video. Digital technology allows for
easy editing and enhancing of videos. 11
12. Displaying Video
There are two ways of displaying video on screen:
Progressive scan
Interlaced scan
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13. Progressive scan
Progressive scan updates all the lines on the screen at the same time. This is known as progressive
scanning. Today all PC screens write a picture like this
Figure 4.1 Progressive scan
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14. Interlaced Scanning
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. Graphically seen a
field is basically a picture with every 2nd line black/white. Here is an image
that shows interlacing so that you can better imagine what happens.
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16. Types of Color Video Signals
Component video
each primary is sent as a separate video signal. The primaries can either be RGB
or a luminance-chrominance transformation of them (e.g., YIQ, YUV). 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.
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17. Component video – 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. 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.
Component video, however, requires more bandwidth and good synchronization
of the three components.
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18. 2. Composite video/1 Signal: color (chrominance) and luminance signals are
mixed into a single carrier wave. Some interference between the two signals is
inevitable. 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.
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19. In NTSC TV, for example, I and Q are combined into a chroma signal, and a
color subcarrier then puts the chroma signal at the higher frequency end of the
channel shared with the luminance signal. The chrominance and luminance
components can be separated at the receiver end, and the two color
components can be further recovered.
When connecting to TVs or VCRs, composite video uses only one wire (and
hence one connector, such as a BNC connector at each end of a coaxial cable or
an RCA plug at each end of an ordinary wire), and video color signals are
mixed, not sent separately. 19
20. 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
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21. 3. S-Video/2 Signal (Separated video): a compromise between component analog
video and the composite video. It uses two lines, one for luminance and another
for composite chrominance signal.
As a compromise, 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 crucial for visual
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22. Humans are able to differentiate spatial resolution in grayscale images much
better than for the color part of color images (as opposed to the “black-and-
white” part). Therefore, color information sent can be much less accurate than
intensity information. We can see only large blobs of color, so it makes sense to
send less color detail.
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24. Video Broadcasting Standards/ TV standards
There are three different video broadcasting standards: PAL, NTSC, and
SECAM
PAL (Phase Alternate Line)
PAL is a TV standard originally invented by German scientists and uses
625 horizontal lines at a field rate of 50 fields per second (or 25 frames per
second). It is used in Australia, New Zealand, United Kingdom, and Europe.
Scans 625 lines per frame, 25 frames per second
Interlaced, each frame is divided into 2 fields, 312.5 lines/field
For color representation, PAL uses YUV (YCbCr) color model
In PAL, 5.5 MHz is allocated to Y, 1.8 MHz each to U and V 24
25. 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. SECAM also uses 625 scan lines per frame,
at 25 frames per second; it is the broadcast standard for France, Russia, and
parts of Africa and Eastern Europe. 25
26. SECAM and PAL are similar, differing 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. They are sent in alternate lines – that is, only
one of the U or V signals will be sent on each scan line.
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27. NTSC (National Television Standards Committee)
The NTSC TV standard is mostly used in North America and Japan. 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 (or be exact, 29.97 fps, 33.37
sec/frame)
Interlaced, each frame is divided into 2 fields, 262.5 lines/field
20 lines reserved for control information at the beginning of each field 27
29. HDTV (High Definition Television)
First-generation HDTV was based on an analog technology developed by Sony
and NHK in Japan in the late 1970s. HDTV successfully broadcast the 1984 Los
Angeles Olympic Games in Japan. Multiple sub-Nyquist Sampling Encoding
(MUSE) 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 a 16:9 aspect ratio. It uses satellite to broadcast ~ quite appropriate
for Japan, which can be covered with one or two satellites.
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30. The Direct Broadcast Satellite (DBS) channels used have a bandwidth of 24
:MHz.
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 therefore its introduction sometimes coincides with the introduction of
digital television (DTV).
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31. Modern plasma television uses this
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. Many people have their preferences
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33. HDTV vs Existing Signals (NTSC, PAL, or SECAM)
The HDTV signal is digital resulting in crystal clear, noise-free pictures and CD
quality sound. It has many viewer benefits like choosing between interlaced or
progressive scanning.
Standard Definition TV (SDTV) ~ the current NTSC TV or higher
Enhanced Definition TV (EDTV) – 480 active lines or higher
High Definition TV (HDTV) – 720 active lines or higher. So far, the popular
choices are 720P (720 lines, progressive, 30 fps) and 1080I (1,080 lines,
interlaced, 30 fps or 60 fields per second). The latter provides slightly better
picture quality but requires much higher bandwidth.
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34. Video File Formats
File formats in the PC platform are indicated by the 3 letter filename extension.
.mov = QuickTime Movie Format
.avi = Windows movie format
.mpg = MPEG file format
.mp4 = MPEG-4 Video File
.flv = flash video file
.rm = Real Media File
.3gp = 3GPP multimedia File (used in mobile phones)
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35. Four Factors of Digital Video
With digital video, four factors have to be kept in mind. These are:
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. 35
36. Color 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 colours).
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37. 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. A standard
analogue video signal displays a full, over scanned image without the borders
common to computer screens. The National Television Standards Committee (
NTSC) standard used in North America and Japanese Television uses a 768 by
484 display.
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38. The Phase Alternative system (PAL) standard for European television is slightly
larger at 768 by 576. Most countries endorse one or the other, but never both.
Since the resolution between analogue video and computers is different,
conversion of analogue video to digital video at times must take this into
account. This can often the result in the down-sizing of the video and the loss of
some resolution.
Image Quality
The last and most important factor is video quality. The final objective is video
that looks acceptable for your application. 38
