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Summary of the 18
Digital Television formats, including 6 HDTV formats
Format
Index |
Vertical
Resolution |
Horizontal
Resolution |
Aspect
Ratio |
Scan
Type |
Refresh
Rate [Hz] |
Type |
| 1 |
480 |
640 |
4:3 |
interlaced |
30 |
SDTV |
| 2 |
progressive |
24 |
EDTV |
| 3 |
30 |
| 4 |
60 |
| 5 |
704 |
4:3 |
interlaced |
30 |
| 6 |
progressive |
24 |
| 7 |
30 |
| 8 |
60 |
| 9 |
704 |
16:9 |
interlaced |
30 |
| 10 |
progressive |
24 |
| 11 |
30 |
| 12 |
60 |
| 13 |
720 |
1280 |
16:9 |
progressive |
24 |
HDTV |
| 14 |
30 |
| 15 |
60 |
| 16 |
1080 |
1920 |
16:9 |
interlaced |
30 |
| 17 |
progressive |
24 |
| 18 |
30 |
Standard Definition Television (SDTV) consists of
the first DTV format of 480i/30. It is equivalent to interlaced video
output of DVD-Video in 4:3 aspect ratio. This format is used for when
bandwidth is a bigger consideration than absolute picture quality. SDTV
uses a data rate of about 4-7 Mbps, so three to six SDTV channels can be crammed
into the same bandwidth as a HDTV channel.
Enhanced Definition Television
(EDTV) is a step up from SDTV, but not quite as good as HDTV.
EDTV consists of some 11 formats as shown in the above table. The vertical
resolution is limited to 480 lines, but horizontal resolution varies 640 to
704 vertical lines. It encompasses both 4:3 and 16:9 aspect ratios, a
number of refresh rates, and both interlaced and progressive scanning.
EDTV is used when better picture quality is desired, but without the full bandwidth
of HDTV.
High Definition Television (HDTV)
uses a data rate of 25 - 27 Mbps for the best possible picture. All HDTV
formats are in 16:9 aspect ratio. The 720 vertical resolution only uses
progressive scanning, but at various refresh rates. The highest resolution
is commonly used in interlaced scanning mode (1080i), due to limitations of
current broadcast and consumer equipment. But the format includes 1080p,
to accommodate future growth as imaging and display technologies catches up.
HDTV is used for premium programming when picture quality is of utmost priority,
and bandwidth is less of a concern. This includes select prime time shows,
major sporting events, and premium movies.
At its highest resolution, HDTV offers 2,116,800 pixels (picture
elements). This is over a six-fold improvement in picture detail of standard
definition television which only has 307,200 pixels. Color resolution
is also improved by a factor of two. All of the DTV formats use MPEG-2
as the video compression standard, just like DVD-Video. MPEG-2 is a flexible
video encoding algorithm and scales up nicely for the higher resolutions of
DTV. With digital transmission, there are no analog transmission artifacts
and degradations such as snow due to weak signal, double images or ghosting
due to multi-path interference of large buildings and structures, and sparkles
due to noise from a vacuum cleaner.
The Audio Format
Not only does DTV bring us a near-perfect picture, but included
in the DTV formats is digital audio as well. Dolby Digital is the standard
digital audio encoding format for all DTV formats. Many of you know Dolby
Digital for its multi-channel surround sound capability from DVD-Video.
What some of you may not realize is that Dolby Digital is more flexible than
just a 5.1-channel surround sound format. Dolby Digital is actually a
scalable digital audio encoding algorithm that supports 1.0-channel (mono) and
2.0-channel (stereo, with optional Dolby Pro-Logic/Pro-Logic II) when the original
programming only has a mono or stereo soundtrack. Dolby Digital only uses
as much data as it needs to encode these 1.0-channel and 2.0-channel audio soundtracks.
Home theater fans will realize of course that Dolby Digital can
scale up to “6.1” extended surround sound as in Dolby Digital EX. If you are
not familiar with surround sound, be sure to read our Surround Sound Tutorial
and Home Theater Receiver Buying Guide for more information.
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