Digital TV with similar definition to analog broadcasts
"SDTV" redirects here. For a television broadcasting network in Shandong Province, see
Shandong Television
.
Standard-definition television
(
SDTV
; also
standard definition
or
SD
) is a television system that uses a resolution that is not considered to be either
high
or
enhanced definition
.
[1]
Standard
refers to offering a similar resolution to the
analog broadcast systems
used when it was introduced.
[1]
[2]
History and characteristics
[
edit
]
SDTV originated from the need for a standard to digitize analog TV (defined in
BT.601
) and is now used for digital TV broadcasts and home appliances such as game consoles and DVD disc players.
[3]
[4]
Digital SDTV broadcast eliminates the
ghosting
and
noisy images
associated with analog systems. However, if the reception has interference or is poor, where the error correction cannot compensate one will encounter various other artifacts such as image freezing, stuttering, or dropouts from missing
intra-frames
or blockiness from missing
macroblocks
. The audio encoding is the last to suffer a loss due to the lower bandwidth requirements.
[
citation needed
]
Standards that support digital SDTV broadcast include
DVB
,
ATSC
, and
ISDB
.
[5]
The last two were originally developed for
HDTV
, but are also used for their ability to deliver multiple SD video and audio streams via
multiplexing
.
PAL and NTSC
[
edit
]
The two SDTV signal types are
576i
(with 576
interlaced
lines of resolution,
[6]
derived from the European-developed
PAL
and
SECAM
systems), and
480i
(with 480 interlaced lines of resolution,
[3]
based on the American
NTSC
system). SDTV
refresh rates
are 25, 29.97 and 30
frames per second
, again based on the analog systems mentioned.
In North America, digital SDTV is broadcast in the same
4:3
aspect ratio
as NTSC signals, with
widescreen
content often being
center cut
.
[5]
In other parts of the world that used the PAL or SECAM color systems, digital standard-definition television is now usually shown with a
16:9 aspect ratio
, with the transition occurring between the mid-1990s and late-2000s depending on the region. Older programs with a 4:3 aspect ratio are broadcast with
a flag
that switches the display to 4:3. Some broadcasters prefer to reduce the horizontal resolution by anamorphically scaling the video into a
pillarbox
.
[
citation needed
]
Pixel aspect ratio
[
edit
]
Pixel aspect ratios
for the scaling of various kinds of SDTV video lines
Video format
|
Display aspect ratio (DAR)
|
Resolution
|
Pixel aspect ratio (PAR)
|
After horizontal scaling
|
480i
|
4:3
|
704?×?480
(
horizontal blanking
cropped)
|
10:11
|
640?×?480
|
720?×?480
(full frame)
|
655?×?480
|
480i
|
16:9
|
704?×?480
(
horizontal blanking
cropped)
|
40:33
|
854?×?480
|
720?×?480
(full frame)
|
873?×?480
|
576i
|
4:3
|
704?×?576
(
horizontal blanking
cropped)
|
12:11
|
768?×?576
|
720?×?576
(full frame)
|
788?×?576
|
576i
|
16:9
|
704?×?576
(
horizontal blanking
cropped)
|
16:11
|
1024?×?576
|
720?×?576
(full frame)
|
1050?×?576
|
The pixel aspect ratio is the same for 720- and 704-pixel resolutions because the visible image (be it 4:3 or 16:9) is contained in the center 704 horizontal pixels of the digital frame. In the case of a digital video line having 720 horizontal pixels (including horizontal blanking), only the center 704 pixels contain the actual 4:3 or 16:9 image, and the 8-pixel-wide stripes on either side are called
nominal analog blanking
or
horizontal blanking
and should be discarded when displaying the image. Nominal analog blanking should not be confused with
overscan
, as overscan areas are part of the actual 4:3 or 16:9 image.
For
SMPTE 259M-C
compliance, an SDTV broadcast image is scaled to 720 pixels wide for every 480 NTSC (or 576 PAL) lines of the image with the amount of non-proportional line scaling dependent on either the display or
pixel aspect ratio
. Only 704 center pixels contain the actual image and 16 pixels are reserved for
horizontal blanking
, though a number of broadcasters fill the whole 720 frames.
[
citation needed
]
The display ratio for broadcast widescreen is commonly 16:9 (pixel aspect ratio of 40:33 for
anamorphic
); the display ratio for a traditional or
letterboxed
broadcast is 4:3 (pixel aspect ratio of 10:11).
An SDTV image outside the constraints of the SMPTE standards requires no non-proportional scaling with 640 pixels (defined by the adopted IBM
VGA
standard) for every line of the image. The display and pixel aspect ratio is generally not required with the line height defining the aspect. For widescreen 16:9, 360 lines define a widescreen image and for traditional 4:3, 480 lines define an image.
See also
[
edit
]
References
[
edit
]
External links
[
edit
]
|
---|
Designation
|
Usage examples
|
Definition (lines)
|
Rate (Hz)
|
Interlaced (fields)
|
Progressive (frames)
|
|
---|
Low,
MP@LL
| |
---|
Standard,
MP@ML
| |
---|
Enhanced,
HMP@HML
| |
---|
High,
MP@HL
|
HDTV
,
BD
,
HD DVD
,
HDV
|
720
|
|
24, 30, 60; 25, 50
|
1080, 1440
|
60; 50
|
24, 30, 60; 25, 50
|
|
---|
Ultra-high
| |
---|
|
---|
Television
|
---|
Analog
| 405 lines
| |
---|
525 lines
| |
---|
625 lines
|
- System B
,
C
,
D
,
G
,
H
,
I
,
K
,
L
,
N
- Color systems:
PAL
,
PAL-N
,
PALplus
,
SECAM
- MAC
|
---|
819 lines
| |
---|
1125 lines
| |
---|
1250 lines
| |
---|
Audio
| |
---|
Hidden signals
| |
---|
Historical
| |
---|
|
---|
Digital
| |
---|
|
|
|