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Standard-definition
television or SDTV
refers to television systems that have a resolution that meets standards but
not considered
high
definition. The term is usually used in reference to
digital television, in particular when
broadcasting at the same (or similar) resolution as analog systems.
In ATSC, SDTV can be
broadcast in 704 pixels × 480 lines with 16:9
aspect ratio (40:33 rectangular pixel), 704
pixels × 480 lines with
4:3
aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3 ratio (and square
pixels). The refresh rate can be any of 24, 30 or 60
pictures
per second.
Digital
SDTV in 4:3 aspect ratio has the same appearance as the
regular analog TV (NTSC,
PAL,
PAL2,
SECAM) minus the
ghosting, snowy
images and static noises. However, if the reception is poor, one
may encounter various other artifacts such as blockiness and stuttering.
Standards
that can broadcast digital SDTV include DVB,
ATSC and
ISDB. The latter two
were originally developed for HDTV, but they have proved to be more often used
for their ability to deliver multiple SD video and
audio
streams
via
multiplexing,
than to use the entire bitstream for one HD
channel.
With
the advent of digital output, television transmission quality is becoming more
sophisticated. Standard Definition television (SDTV) and High Definition
television (HDTV) are two of the new formats. SDTV is a digital format that
provides a high quality picture, very similar to that of digital versatile
disk.
The
quality of these new digital transmissions will become the standard for the
future of broadcasting. SDTV is a lower resolution picture than HDTV. The
images on SDTV will be of better quality than those of today's TV screens. They
will also still have stereo sound.
The
difference between SDTV and HDTV is that the signal on SDTV is more compressed
than that of HDTV. As the digital signal is compressed, broadcasters can
transmit five SDTV programs, whereas HDTV can only broadcast one. Multiple program
broadcasting, called multicasting, was not previously available with analog
transmissions. The picture definition of SDTV is also slightly lower than on
HDTV.
SDTV
will give a greater range of choice in the type of viewing material you will be
able to access. Children's programs, documentaries, films, and public affairs
-- the choice will be far greater than before. It will be the equivalent of
digital satellite services such as the Dish Network or Direct TV.
Most
of the normal TV sets used today cannot receive digital transmissions. You will
need a DTV receiver in order to accept them. DTV receivers are available at the
moment; they work by connecting your television to an output. However, they are
of limited performance quality. You will be able to watch SDTV and HDTV
programs, but they will not be true, High Definition picture quality.
All
broadcasters are now required by the FCC to use the new digital system. In
order to fully experience SDTV or HDTV, you will need to buy a new television
set. High definition sets first appeared in 1998. These television sets were
very expensive, much like when the first compact disc players appeared. The
price has dropped significantly since then, as the diversity of televisions
available has grown. See also
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