- Standard-definition television
Standard-definition television or SDTV refers to television systems that have a resolution that meets standards but not considered either enhanced definition or 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
16:9aspect ratio (40:33 rectangular pixel), 704 pixels × 480 lines with 4:3aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3ratio (and square pixels). The refresh ratecan be any of 24, 30 or 60 frames 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 last two were originally developed for HDTV, but they have proved to be more often used for their ability to deliver multiple SD videoand audio streams via multiplexing, than to use the entire bitstreamfor one HD channel.
When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution of 720 or 704 format.
DTV in USA
In the USA, SDTV refers to digital television broadcast in 4:3 aspect ratio, the same aspect ratio as NTSC signals. [http://www.fcc.gov/cgb/consumerfacts/digitaltv.html All-Digital Television Is Coming (And Sooner Than You Think!) ] ] When a television set is labeled "SDTV", this means that the set includes an ATSC tuner, but scans its picture in the same 480i pattern used in NTSC.
digital audio broadcasting
* [http://lurkertech.com/lg/video-systems Programmer's Guide to Video Systems: in-depth technical info on 480i,576i,etc. including software implications]
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