Standard-definition television
Encyclopedia
Sorete-definition television (SDTV) is a television system that uses a resolution that is not considered to be either enhanced-definition television
(EDTV) or high-definition television
(HDTV). The term is usually used in reference to digital television
, in particular when broadcasting at the same (or similar) resolution as analog systems. The two common SDTV signal types are 576i
, derived from the European-developed PAL
and SECAM
systems with 576 interlaced lines of resolution; and 480i
, based on the American National Television System Committee NTSC
system.
In the USA, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals. However, in areas that used the PAL or SECAM analog standards, standard-definition television is now usually shown with a 16:9
aspect ratio
, with the transition occurring between the mid-1990s and mid-2000s. Older programs with a 4:3 aspect ratio are shown in 4:3.
Soretes that support digital SDTV broadcast include DVB, ATSC Standards and ISDB
. The last two were originally developed for HDTV, but are more often used for their ability to deliver multiple SD video and audio streams via multiplexing
, than for using the entire bitstream
for one HD channel
.
In ATSC Standards, SDTV can be broadcast in 720 pixels × 480 lines with 16:9 aspect ratio
(40:33 rectangular (unsquare) pixel
), 720 pixels × 480 lines with 4:3]aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3 ratio. The refresh rate
can be 24, 30 or 60 frames per second.
Digital SDTV in 4:3 aspect ratio has the same appearance as regular analog TV (NTSC, PAL, SECAM) without the ghosting
, snowy images and white noise
. However, if the reception is poor, one may encounter various other artifacts such as blockiness and stuttering.
s for various kinds of SDTV video signal. Note that the actual image (be it 4:3 or 16:9) is always contained in the center 704 horizontal pixels of the digital frame, regardless of how many horizontal pixels (704 or 720) are used. In case of digital video signal having 720 horizontal pixels, only the center 704 pixels contain actual 4:3 or 16:9 image, and the 8 pixel wide stripes from either side are called nominal analogue blanking
and should be discarded before displaying the image. Nominal analogue blanking should not be confused with overscan
, as overscan areas are part of the actual 4:3 or 16:9 image.
The pixel aspect ratio
is always the same for corresponding 720 and 704 pixel resolutions because the center part of a 720 pixels wide image is equal to the corresponding 704 pixels wide image
Enhanced-definition television
Enhanced-definition television, or extended-definition television, is a United States Consumer Electronics Association marketing shorthand term for certain digital television formats and devices...
(EDTV) or high-definition television
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
(HDTV). The term is usually used in reference to digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
, in particular when broadcasting at the same (or similar) resolution as analog systems. The two common SDTV signal types are 576i
576i
576i is a standard-definition video mode used in PAL and SECAM countries. In digital applications it is usually referred to as "576i", in analogue contexts it is often quoted as "625 lines"...
, derived from the European-developed PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
systems with 576 interlaced lines of resolution; and 480i
480i
480i is the shorthand name for a video mode, namely the US NTSC television system or digital television systems with the same characteristics. The i, which is sometimes uppercase, stands for interlaced, the 480 for a vertical frame resolution of 480 lines containing picture information; while NTSC...
, based on the American National Television System Committee NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
system.
In the USA, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals. However, in areas that used the PAL or SECAM analog standards, standard-definition television is now usually shown with a 16:9
16:9
16:9 is an aspect ratio with a width of 16 units and height of 9. Since 2009, it has become the most common aspect ratio for sold televisions and computer monitors and is also the international standard format of HDTV, Full HD, non-HD digital television and analog widescreen television ...
aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
, with the transition occurring between the mid-1990s and mid-2000s. Older programs with a 4:3 aspect ratio are shown in 4:3.
Soretes that support digital SDTV broadcast include DVB, ATSC Standards and ISDB
ISDB
Integrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio and television stations. ISDB replaced the previously used MUSE "Hi-vision" analogue HDTV system...
. The last two were originally developed for HDTV, but are more often used for their ability to deliver multiple SD video and audio streams via multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
, than for using the entire bitstream
Bitstream
A bitstream or bit stream is a time series of bits.A bytestream is a series of bytes, typically of 8 bits each, and can be regarded as a special case of a bitstream....
for one HD channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
.
In ATSC Standards, SDTV can be broadcast in 720 pixels × 480 lines with 16:9 aspect ratio
Aspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
(40:33 rectangular (unsquare) pixel
Pixel aspect ratio
Pixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel....
), 720 pixels × 480 lines with 4:3]aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3 ratio. The refresh rate
Refresh rate
The refresh rate is the number of times in a second that a display hardware draws the data...
can be 24, 30 or 60 frames per second.
Digital SDTV in 4:3 aspect ratio has the same appearance as regular analog TV (NTSC, PAL, SECAM) without the ghosting
Ghosting (television)
In television, a ghost is a replica of the transmitted image, offset in position, that is super-imposed on top of the main image on an analogue broadcast.-Common causes:Common causes of ghosts are:...
, snowy images and white noise
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
. However, if the reception is poor, one may encounter various other artifacts such as blockiness and stuttering.
Pixel aspect ratio
When standard-definition television signals are transmitted in digital form, its pixels have rectangular shape, as opposed to square pixels that are used in modern computer monitors and modern implementations of HDTV. The table below summarizes pixel aspect ratioPixel aspect ratio
Pixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel....
s for various kinds of SDTV video signal. Note that the actual image (be it 4:3 or 16:9) is always contained in the center 704 horizontal pixels of the digital frame, regardless of how many horizontal pixels (704 or 720) are used. In case of digital video signal having 720 horizontal pixels, only the center 704 pixels contain actual 4:3 or 16:9 image, and the 8 pixel wide stripes from either side are called nominal analogue blanking
Nominal analogue blanking
Nominal analog blanking or nominal analogue blanking is the outermost part of the overscan of a standard definition digital television image...
and should be discarded before displaying the image. Nominal analogue blanking should not be confused with overscan
Overscan
Overscan is extra image area around the four edges of a video image that may not be seen reliably by the viewer. It exists because television sets in the 1930s through 1970s were highly variable in how the video image was framed within the cathode ray tube .-Origins of overscan:Early televisions...
, as overscan areas are part of the actual 4:3 or 16:9 image.
| Video Format | Resolution | Pixel Aspect Ratio | Equivalent square-pixel resolution |
| PAL 4:3 | 704×576 | 12:11 | 768×576 |
| PAL 4:3 | 720×576 | 12:11 | 786×576 |
| PAL 16:9 | 704×576 | 16:11 | 1024×576 |
| PAL 16:9 | 720×576 | 16:11 | 1048×576 |
| NTSC 4:3 | 704×480 | 10:11 | 640×480 |
| NTSC 4:3 | 720×480 | 10:11 | 654×480 |
| NTSC 16:9 | 704×480 | 40:33 | 854×480 |
| NTSC 16:9 | 720×480 | 40:33 | 872×480 |
The pixel aspect ratio
Pixel aspect ratio
Pixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel....
is always the same for corresponding 720 and 704 pixel resolutions because the center part of a 720 pixels wide image is equal to the corresponding 704 pixels wide image
See also
- Digital audio broadcastingDigital audio broadcastingDigital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
- Pixel aspect ratioPixel aspect ratioPixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel....
- MPEG
- SBTVDSBTVDISDB-T International or SBTVD, short for Sistema Brasileiro de Televisão Digital is a technical standard for digital television broadcast used in Brazil, Peru, Argentina, Chile, Venezuela, Ecuador, Costa Rica, Paraguay, Philippines, Bolivia, Nicaragua and Uruguay, based on the Japanese ISDB-T...