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What is
DTV
Because these signals are digital,
the resulting picture you receive is identical to what the station sends out.
The old problems that plagued analog reception with antennas, such as ghosting,
snow and unclear pictures, are completely eliminated. The network programming
available through broadcast television is now available, for free, in digital
clarity. The picture quality is at least as good as, and in most cases superior
to, analog reception, cable, digital cable, and digital satellite. In
particular, this is the only way to get most network HDTV programming in high
definition.
Why
Change to DTV
Today's television system has served the
American public well for almost three generations. Over the years, additional
features and functions, such as color, stereo sound, remote control, cable
channels, closed captioning, and parental control features were developed. Even
with these improvements, TV sets became less expensive and more affordable.
However, today's television system is now
showing its age. A transition to digital is occurring in all media technologies.
Direct broadcast satellite providers, for example, have offered digital service
since their inception. In contrast, the shortcomings of the 50-year-old analog
technology used by broadcasters, such as limited resolution and color
rendition as well as problems with "ghosts" and interference from
other radio sources, have become increasingly apparent as consumer TV sets
have become larger and more technologically advanced.
The quality of DTV and HDTV is such
that NASA used an "off the shelf" Sony HDW-700 HDTV camcorder
for the first time on the space shuttle in December, 2001.
(Expedition Three, ISS Mission
7A.1, STS-105.)
Therefore, at the request of the television
broadcast industry, the FCC sponsored an effort to investigate the possibility
of significantly improving the technical quality of today's television system.
In 1988, scientists and engineers in the
broadcast, cable, and consumer electronics industries and in government worked
on the development of this new television system. Many different approaches were
developed and tested. Today's DTV system represents the culmination of this
work. DTV eventually will replace today's analog television service. After a
transition period that allows stations to construct DTV transmission facilities
and consumers gradually to replace their TV sets, broadcasts using the existing
analog television system will cease and all over-the-air broadcast television
service will be provided with the new DTV system
The FCC required the top TV networks to
broadcast a digital signal in the 10 biggest markets by May 1999, which
represent 30 percent of TV households in the U.S. The networks plan to expand
digital coverage and phase out analog TV broadcasts entirely by the end of 2006.
In fact, you may have noticed that many prime-time programs are now being
broadcast in HD.
Why are stores still selling analog TV's? If
I buy one, am I not buying something that will be obsolete in a few years?
Not really. TV stations and media production
companies have to upgrade equipment in order to produce HDTV programming, a slow
and costly process - could be as much as a trillion dollars before it's all over
with. For this reason, the FCC created a transition plan slated to end in 2006
(but don't be surprised if it is pushed back again). Also, HDTV sets are
currently more expensive than analog TVs. It is expected that when consumer
demand for the sets increases, production will also increase and prices will
drop. Also, expect a number of manufacturers to supply converter boxes to allow
analog TV's to receive a digital signal.
Why
Digital Pictures Are So Good
Digital TV looks much better than
traditional television because of the way new digital sets can display
pictures. Television screens on all TV sets are made up of many horizontal lines and dots ("pixels"). Pixels are hundreds of thousands of tiny dots
that make up a complete picture.
We cannot see the pixels because
they are extremely small, but if you looked at a typical newspaper photograph
through a magnifying glass, you would be able to see dots or pixels that the
human eye normally cannot see. Today’s form of television (called
"analog") uses about 300,000 pixels on a traditional screen.
What is
HDTV
HDTV is an acronym for high-definition
television. HDTV uses the same amount of bandwidth (6 megahertz) as used in the
current analog system, but HDTV can transmit more than six times the information
as the analog system. This translates to higher quality in picture and sound.
Currently, television pictures are made up of
525 lines that are scanned horizontally. HDTV pictures are created by scanning
1,080 lines. Adding twice the amount of lines multiplies the amount of pixels
(the small dots that create the picture).
Current sets have about 300,000 pixels, while
the HDTV screen is composed of more than 2 million pixels. Many
more pixels and lines result in digital TV pictures that are dramatically more
vivid and detailed than traditional television.
A conventional, analog TV uses a cathode ray
tube (CRT or picture tube) to deliver images to you, which limits the quality of
the image. The screen resolution of an analog TV is about 512x400 pixels. HDTV
uses a digital display, like your computer monitor, and the screen resolution is
at least 1280x720 pixels, which is comparable to a high-end computer display. A
higher screen resolution means a crisper, clearer picture.
In addition to dramatically improved picture
quality, HDTV also offers a wider format. This makes an HDTV image more like a
movie-screen image. The width-to-height ratio, called the aspect ratio,
of HDTV is 16:9. Analog TV has an aspect ratio of only 4:3.
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| 4:3 |
16:9 |
The difference in aspect ratio is most
noticeable when watching theatrical movies on TV. For analog TV, the movie must
be cut down in a process called "pan and scan," in which a part of
every scene is deleted to fit the lower aspect ratio. On earlier DVD players and
discs you may see this as an option. The only way to see the entire movie scene
on an analog TV is to "letterbox" the movie. In letterboxing, the full
movie is shown in the middle of the screen with black bars at the top and
bottom. If you are viewing in letterbox, even with a 31" TV, the picture may be
small as a large part of the screen isn't being used. HDTV eliminates letterboxing and
allows you to see the complete movie on the whole TV screen.
In addition to picture quality, there are 5.1
channels of CD-quality digital audio. Current stereo TV sets offer only two
channels of audio. HDTV delivers true surround sound: front speakers on the
right, center and left, along with two back speakers and a subwoofer.
How big a TV set do I
need to buy and why does it have to be bigger?
The advertised size of a television sets in the
U.S. is the size of the viewable picture, measured diagonally. These diagonal
measurements can be misleading when comparing conventional and DTV sets. Here's
a scale drawing comparing a 25" standard set -- a popular size -- with a
theoretical 25" DTV screen:
Analog 3x4 Set vs.
Digital 16x9 Set
A wide-screen DTV set will look quite a bit
smaller than an NTSC set of the same advertised size. One way to compare NTSC
and DTV sets more fairly is to compare the diagonal measurement of the NTSC
screen with the width of the DTV screen. Continuing the example, a 28" or
29" (advertised) DTV set will appear approximately as large as a 25"
NTSC set:
The lesson? Bring a tape measure to the store
when shopping for an DTV set. Be sure to check how deep the set is
also;first-generation DTVs will have very long picture tubes. You'll also need a
strong friend or two to help lug the thing home. The new sets will be HEAVY
until they perfect the flat plasma displays.
Interacting
with TV Programs
Digital technology also provides
the ability of broadcasters to send extra material with certain programs — and
permit viewers to interact on-screen with that extra material. Television time
is extremely valuable, and most programs cannot include all of the scenes, extra
facts and additional material for students and other viewers in the allotted
time. By sending this supplemental material (not immediately visible on-screen)
within a show’s digital broadcast signal, digital broadcasters provide viewers
with the option to place that extra material on-screen.
It happens when a viewer sees a
small icon pop up in the corner of the TV set. Using a special TV remote, for
example, viewers may automatically "pause" the actual TV show and
address new information on-screen, such as answers to questions, related maps,
or even watch related video in a small on-screen window from someone who isn’t
in the main program. And much of this "enhanced" material can be
recorded for later use — and used over and over again.
Will
my existing VCR's, DVD's and camcorder work?
HDTV sets are "backward compatible,"
meaning all existing analog equipment (VCRs, DVD players, camcorders, video
games, etc.) will work on digital TV sets, but not in high definition. Their
video will be displayed in the maximum resolution that each product is capable
of.
What about digital
signals from cable or satellite?
Aren't some cable and satellite systems already
transmitting DTV and HDTV? Will new digital TV's display signals from these
systems?
Possibly. Some cable and satellite systems already use digital technology to
transmit their television programming. And in these cases, they have developed
several different transmission standards and image formats that require
consumers to rent or purchase a converter box. Most of these standards are not
compatible with each other, much less the new ATSC standard for digital
television. These industries are currently working on ways of modifying their
technology to incorporate the new DTV standard, and should have a solution in
the near future. It is to their advantage to get in compliance with ATSC
standards....rapidly.
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