Low-definition television
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Low-definition television or LDTV refers to television systems that have a lower resolution than standard-definition television systems. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as analog systems.
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[edit] Sources
The most common source of LDTV programming is the Internet, where mass distribution of higher resolution files could overwhelm servers and take too long to download. Portable devices such as Apple’s video iPod, or Sony’s PlayStation Portable use LDTV video, as higher resolution files would be excessive to the needs of their small screens (320 × 240 and 480 × 272 pixels respectively). The current generation of iPods still have LDTV screens, as does the iPhone. (320×480)
An upcoming source of LDTV using standard broadcasting techniques are mobile TV services powered by DVB-H or DMB.
The Video CD format uses a progressive LDTV signal (352 × 240 or 288), which is half the vertical resolution of SDTV.
A professionally duplicated VHS tape could be considered borderline SDTV, but any attempt to use VHS for production will yield results comparable to LDTV. VHS supports interlace and high motion, which are not typical of LDTV signals.
Older video game consoles such as the Nintendo Entertainment System generated a non-standard version of NTSC or PAL in which the two fields did not interlace, and instead were displayed directly on top of each other, keeping the orientation of the scanlines constant. This would be 240p and 288p respectively.
The NTSC PlayStation, for example, was capable of true 480i output, but most games used 240p mode due to limited graphics and CPU power [1].
More recent systems now always use properly interlaced NTSC or PAL, except when running games designed for older, but compatible systems. The PS2 generates 240p/288p if a PS1 game calls for this mode. Similarly, the Wii switches to a 240p mode in the Virtual Console for games designed for it, excluding the N64, for which games are rendered with 480 lines.
[edit] Teleconferencing LDTV
An upcoming source of LDTV using standard broadcasting techniques are mobile TV services powered by DVB-H or DMB -- however this kind of LDTV transmission technology is based on existent LDTV teleconferencing standards that have been in place for a decade or more.
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