MULTECH2 LESSON 5.pdf

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Fundamental
Fundamental
Concepts in Video
Concepts in Video
Multimedia Technology - Midterm
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Analog Video Digital Video
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TYPES OF VIDEO
Analog technology requires
information representing
images and sound to be in a real
time continuous-scale electric
signal between sources and
receivers.
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.

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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. 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.
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ANALOG VIDEO

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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 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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ANALOG VIDEO

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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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ANALOG VIDEO
Figure 5. 1 Scanning video

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the ability to randomly access the storage of video and
Compress the video stored.
There are two significant advantages for using computers for digital video:
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.
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DIGITAL VIDEO

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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. 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.
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DIGITAL VIDEO

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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
The advantages of digital representation for video are many. It permits
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DIGITAL VIDEO

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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.
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ANALOG VS. DIGITAL VIDEO

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Progressive scan
Interlaced scan
There are two ways of displaying video on screen:
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DISPLAYING VIDEO

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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
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PROGRESSIVE SCAN
Figure 5. 2 Progressive scan

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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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INTERLACED SCANNING
Figure 5. 3 Interlaced Scanning

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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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TYPES OF COLOR VIDEO SIGNALS
Component video

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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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Component video

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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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Composite video/1 Signal:

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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.
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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. 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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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 perception.
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S-Video/2 Signal

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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.
Table 5.1 Types of Color Video Signals
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S-Video/2 Signal

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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
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.
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VIDEO BROADCASTING STANDARDS/
TV STANDARDS
PAL (Phase Alternate Line)
There are three different video broadcasting standards: PAL, NTSC, and SECAM

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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.
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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TV STANDARDS
SECAM (Sequential Color with Memory)

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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
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.
So a maximum of 485 lines of visible data.
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TV STANDARDS
NTSC (National Television Standards Committee)

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Table 5.2 Comparison of analog broadcast TV systems.
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TV STANDARDS

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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. The Direct Broadcast
Satellite (DBS) channels used have a bandwidth of 24 :MHz.
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TV STANDARDS
HDTV (High Definition Television)

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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
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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TV STANDARDS

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Table 5.3 Advanced Digital TV Formats Supported by ATSC
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TV STANDARDS

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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.
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.
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TV STANDARDS
HDTV vs Existing Signals (NTSC, PAL, or SECAM)

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.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)
File formats in the PC platform are indicated by the 3 letter filename extension.
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TV STANDARDS
Video File Formats

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Frame Rate
Color Resolution
Spatial Resolution
Image Quality
With digital video, four factors have to be kept in mind. These are:
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FOUR FACTORS OF DIGITAL VIDEO
Four Factors of Digital Video

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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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Frame Rate

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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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Color Resolution

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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. 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.
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Spatial Resolution

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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.
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Spatial Resolution

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The last and most important factor is video quality. The final objective is video that looks
acceptable for your application.
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Image Quality

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