Matakuliah
Tahun
: O0382 – Dasar-dasar Produksi Siaran Televisi
: 2010
ANALOG AND DIGITAL TELEVISION
Pertemuan 2
Analog and Digital Television (1/2)
To really understand how various digital elements of the television
system interact-such as digital cameras and nonlinear editing systemwe need to know what the basic digital processes are and how they
differ from analog ones.
Basic Image Creation
The inside of the television screen is dotted with light-sensitive picture
elements or pixels (round dots or tiny rectangles), that light up when hit
by the beam.
If the beam is powerful the dots light up brightly and if the beam is weak
then the dots light up partially. If the beam is really tired then the dots
don’t light up at all.
The traditional television system consists of 525 lines on the screen
and the system was developed by the National Television System
3
Committee (NTSC) system.
Analog and Digital Television (2/2)
To produce an image, the electron beam scans the odd-numbered lines
then jumps back to the top of the screen and scans the even-numbered
lines. The complete scans of all odd and even-numbered lines which
takes 1/60 seconds is called a field, and is called a frame. In traditional
NTSC, there are 30 frames per second.
Basic Colors of the Display
All beautiful images seen on television are a mixture of 3 (three) basic
colors: red, green, and blue. Depending on how hard the pixels are hit
by electronic beam, the colors light up in different intensities. The blend
of these intensities produces all the other colors.
4
What Digital is All About (1/13)
Why digital?
The goal of digital system is basically to improve the quality of picture.
The digital system simply ignores interruptions and reacts only if the
switch triggers the expected on/ off mode of the light. The interruptions are
caused by distortion and error when the system reads the data.
The difference between analog and digital
Analog system processes and records a continuous signal that fluctuates
exactly like the original signal.
As digital processing changes ramp into concrete values. This process is
called digitization.
Surely, the camera lenses used to work in digital system requires a higher
resolution in order to produce clearer picture.
5
What Digital is All About (2/13)
The process of Digitization
Digitizing an analog video signal is a four-step process: anti aliasing,
sampling, quantizing, and coding. The followings are the
explanation of each process:
 Anti-aliasing: the extreme frequencies of the analog signal that are
unnecessary for its proper sampling are filtered out.
 Sampling: the number of points along the ramp (analog signal) are
selected for building the steps (digital values). The sampling rate of
a video signal is usually expressed in megahertz (MHz).
 Quantizing: build and check how high or low each step is relative to
scale-the quantizing level. The height of each step is measured
and an 8-bit quantizing has a maximum number of 256 steps.
 Coding: also called encoding, changes the quantization numbers of
each step to binary numbers, consisting of 0’s and 1’s.
6
What Digital is All About (3/13)
Benefits of Digital Television
Some major advantages of DTV (Digital Television) over the analog signal
are:
 Aspect ratio
Aspect ratio is the width to height proportions of the television screen.
The 4 X 3 aspect ratio
The traditional television screen and of computer screen, which means
the frame is four units by three units high or 1.33:1. The advantage of this
classic aspect ratio is that the difference between the screen width and
the screen height is not so clearly pronounced. The disadvantage is that
it does not accommodate wide-screen movies that have the much more
horizontally stretched aspect ratio.
The 16 x 3 aspect ratio
The horizontally stretched aspect ratio of DTV system is 16x9 or 1.78:1.
7
This ratio resembles movie screen more than the traditional one.
What Digital is All About (4/13)
 Quality
DTV offers extremely sharp and crisp pictures with fine details and
improved colors.
 Computer compatibility and flexibility
Signal of DTV can be directly transferred to a computer without the need
for digitization. This is important for creating special effects and
computer generated images.
 Signal transport
Through digital signal, data can be transferred with minimum signal
distortion and interference compare to analog binary system mode of
transferring data that is extremely robust and highly resistant to signal
distortion and interference.
Furthermore, the size of digital signal can be reduced dramatically
without sustaining any noticeably damage through a process called
8
compression.
What Digital is All About (5/13)
 Compression
Compression is the temporary rearrangement or elimination of
redundant information for easier storage and signal transmission.
Digital information can be compressed by regrouping the original data
without throwing any of it.
With decoding process, the data can be restored to their original
position for the output identical to the original input.
One of the most widely used digital compression standards for still
images is JPEG (Joint Photographic Experts Group) and moving JPEG
for moving computer images. Another compression standard for highquality video is MPEG-2 (Moving Picture Expert Group).
Both compression techniques are lossy compression techniques – the
compression technique that regenerates image with similar number of
pixels and values as the original.
9
What Digital is All About (6/13)
The advantage of lossless compression is that the original image is
returned without diminished quality. The disadvantage is that it takes
more storage space and takes more time to transport and bring back from
storage. Most image compression techniques are lossy kind.
Scanning Systems
Standard television uses interlaced scanning; while digital television
systems produce high resolution pictures through either interlaced or
progressive scanning.
Interlaced and progressive scanning
In interlaced scanning the electron beam reads all the odd-numbered
lines then jumps back to the top to read all even-numbered lines. In this
process some of the line get lost. The lines we actually see on the screen
10
are called active or visible lines.
What Digital is All About (7/13)
The 525 lines of NTSC analog television are divided into 2 (two) fields:
262.5 lines for the first field and another 262.5 for the second field.
The beam scans 60 alternate field (30 complete frames), each second.
This scanning speed is so fast that we perceive the two fields as
complete, flicker-free picture. Of these 525 lines only 480 are visible or
‘active’.
The reason for interlacing the lines is to save bandwidth, the electronic
pipeline that transports the television signal. By splitting each frame in
half and sending the two halves then the video information is reduced
and you get by with a smaller bandwidth.
Retrace and blanking
Both interlaced and progressive scanning system use retrace and
blanking. The repositioning of the beam from the end of the scanned line
11
to the starting point of the next is called horizontal retrace.
What Digital is All About (8/13)
When the beam reaches the end of the last line and jumps back to the
starting point of line 1 then it is referred to as vertical retrace.
The blanking process happens when the beam won’t light up any pixels
during horizontal and vertical retrace to avoid picture interference with the
original scan. Horizontal blanking occurs during horizontal retrace and
vertical blanking occurs during vertical retrace.
The progressive scanning system
Technically, in the progressive scanning system the scanning system
waits until a whole frame is formed before sending or displaying it on the
screen. In this system, the electron beam scans line by line and after the
last line has been scanned then the beam jumps back to its original
starting point at the top left of the screen. The beam scans all lines
progressively as it is called.
12
What Digital is All About (9/13)
DTV Systems
After years of wrangling over the former ATV (advanced television) and
DTV (digital television) scanning standards, the industry seems to have
settled on three systems: the 480p, the 720p, and the 1080i.
The 480p system
The 480p system uses 480 lines that are scanned progressively every
1/60 second. The number of active (visible) lines in this system is
identical to the number of lines in a traditional analog television set. In
480p system, instead of generates 60 fields (30 frames) per second of
standard television, it generates 60 complete frames per second.
The main reason for this higher refresh rate (frame rate) of the 480p
system and of all other progressive scanning systems is to avoid flicker.
13
What Digital is All About (10/13)
Flicker
Flicker is noticeable periodic brightness variations from frame to frame. It
occurs when the pixels of one frame start to fade before they are
reactivated by new frame scan. To avoid such premature pixel
starving, the electron beam has to scan quite a bit faster than in
interlacing scanning. For many DTV systems, the minimum frame rate
must be 60fps (frames per second), computer screens have an even
faster refresh rate of 72 or more fps.
The 720p system
The 720 visible, or active, lines (of 750 actual scanning lines) that are
scanned progressively in the 720ps system and its refresh rate of 60
contribute to true high-definition television images. This will produce
superior resolution and color fidelity pictures. The advantages of 720p
system are a relatively low number of scanning lines, efficient
14
compression, and ease of conversion when transmitted via cable.
What Digital is All About (11/13)
The 1080i system
The 1080i system (1080 visible lines of 1125 total lines) uses
interlaced scanning. The high number of scanning lines of 1080i
system improves the resolution of the television picture.
The relative picture quality of the three standards depends on the
program content. A bad program remains bad even when received in
digital form; a good program is good even if the picture quality is
slightly inferior. The picture quality becomes a real issue when using
HDTV system for instructional or training purposes, such as medical
programs.
15
What Digital is All About (12/13)
Flat Panel Displays
High-definition receivers development is in line with the
development DTV. The advantage of flat-panel displays over regular
television receivers or large-screen projection systems is that flat
panels can be made very large without getting thicker and that the
flat-panel displays can be hung on a wall in order to reduce space
utilization.
As with video technologies, there are 2 (two) incompatible types
of flat-panel displays that can reproduce high-definition video images:
plasma display and liquid crystal display.
16
What Digital is All About (13/13)
Plasma display panel
The plasma display panel uses 2 (two) transparent (usually glass) wired
panels that sandwich a thin layer of gas. When the gas receives the
voltages of the video signal, it activates the RGB (red, green, blue) dots
that are arranged very much like those of the standard television
receiver.
Liquid crystal display
The LCD also uses transparent sheets but instead of gas the panels
sandwich a liquid whose crystal molecules change when an electric
current is applied. Rather than RGB dots, LCD uses tiny transistors that
light up according to the voltages of the video signals. Both flat-panel
displays can produce true high-definition pictures.
17