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Low-definition television or LDTV refers to television systems that have a lower screen 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 low-definition analog TV systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan TV systems..



The most common source of LDTV programming is the Internet, where mass distribution of higher-resolution video files could overwhelm computer servers and take too long to download. Most mobile phones and 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 have LDTV screens, as does the iPhone (480×320).

A VHS videotape could be considered SDTV due to its resolution (approximately 320×486), but any attempt to use VHS for professional production will yield results comparable to LDTV. VHS supports interlace and high motion, which are not typical of LDTV signals. Professional-level Betacam SP tape produces 440×486; some college TV studios use Super VHS at 560×486.

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 is equivalent to 240p and 288p respectively. The Video CD format was introduced on such a console (CD-i), and it likewise uses a progressive LDTV signal (352×240 or 352×288), which is half the vertical resolution of SDTV.

In contrast, the NTSC PlayStation was capable of true 480i output, but most games used 240p mode due to limited graphics and CPU power.

More recent game systems tend to use only properly interlaced NTSC or PAL in addition to higher resolution modes, except when running games designed for older, compatible systems in their native modes. The PlayStation 2 generates 240p/288p if a PlayStation game calls for this mode.

Teleconferencing LDTV

Upcoming sources of LDTV using standard broadcasting techniques include mobile TV services powered by DVB-H, DMB, or ATSC-M/H. However, this kind of LDTV transmission technology is based on existent LDTV teleconferencing standards that have been in place for a decade or more.

See also




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