Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition TV systems. The term is usually used in reference to digital TV, 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 Video CD format uses a progressive scan LDTV signal (352×240 or 352×288), which is half the vertical and horizontal resolution of full-bandwidth SDTV. However, most players will internally upscale VCD material to 480/576 lines for playback, as this is both more widely compatible and gives a better overall appearance. No motion information is lost due to this process, as VCD video is not high-motion and only plays back at 25 or 30 frames per second, and the resultant display is comparable to consumer-grade VHS video playback.
For the first few years of its existence, YouTube offered only one, low-definition resolution of 320x240 at 30fps or less, later extending first to widescreen 426×240, then to gradually higher resolutions; once the video service had become well established and had been acquired by Google, it had access to Google's radically improved storage space and transmission bandwidth, and could rely on a good proportion of its users having high-speed internet connections. In 2013, YouTube extended further into the LDTV realm by adding an even lower 256×144 resolution with a halved framerate giving an overall effect reminiscent of early online video streaming attempts using RealVideo or similar services, where 160×120 at single-figure framerates was deemed acceptable to cater to those whose network connections could not even sufficiently deliver 240p content.
Older video game consoles and home computers often generated a technically compliant NTSC or PAL signal (480i and 576i respectively) but only sent one field type rather than alternating between the two. This created a 240 or 288 line progressive signal, which in theory can be decoded on any receiver that can decode normal, interlaced signals. Since the shadow mask and beam width of standard CRT televisions were designed for interlaced signals, these systems produced a distinctive fixed pattern of alternating bright and dark scan lines; many emulators for older systems offer video filters to recreate this effect.
With the late 1980s introduction of 16-bit and 32-bit computers/game consoles, such as the Atari ST, the Commodore Amiga, the Super NES, and the Sega Genesis, outputs up to 480i/576i were supported for the first time, but rarely used due to heavy demands on processing power and memory. Standard resolutions also had a tendency to produce noticeable flicker at horizontal edges unless employed quite carefully, such as using anti-aliasing, which was either not available or computationally exorbitant. Thus, 240p/288p remained the primary format on most games of the fourth and fifth generation consoles (including the Sega Saturn, the Sony PlayStation and the Nintendo 64). With the advent of sixth generation consoles and the launch of the Dreamcast, 480i/576i use became more common, and 240p/288p usage declined.
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, as do many Virtual Console emulated games on the Nintendo Wii. Nintendo's official software development kit documentation for the Wii refers to 240p as 'non-interlaced mode' or 'double-strike'.
Shortly after the launch of the Wii Virtual Console service, many users with component video cables experienced problems displaying some Virtual Console games due to certain TV models/manufacturers not supporting 240p over a component video connection. Nintendo's solution was to implement a video mode which forces the emulator to output 480i instead of 240p, however many games released prior were never updated.
Sources of LDTV using standard broadcasting techniques include mobile TV services powered by DVB-H, 1seg, DMB, or ATSC-M/H. However, this kind of LDTV transmission technology is based on existent LDTV teleconferencing standards that have been in place since the late 1990s.
|MMS-Small||96p||128×96||12,288||4:3||Lowest size recommended for use with 3GPP video transmitted by MMS to/from cellular phones, matching resolution of smallest generally used color cellphone screen.|
|QQVGA||120p||160×120||19,200||4:3||Used with some webcams and early colour-screen cellular phones, commonly used in early desktop computer and online video applications. Lowest commonly used video resolution.|
|QCIF Webcam||144p||176×144||25,344||11:9||Approximately one-sixth analogue PAL resolution (one-half horizontal, one-third vertical). Also the size recommended for "medium" quality MMS videos.|
|144p||144p||192×144||27,648||4:3||The resolution 192×144 is used when 144p is selected on a fullscreen YouTube video.|
|YouTube 144p||144p||256×144||36,864||16:9||One tenth of 1440p. The lowest resolution on YouTube.|
|QVGA, NTSC square pixel||240p||320×240||76,800||4:3||Comparable to "low resolution" output of many popular home computers and games consoles, including VGA "Mode X". Used in some webcams and for video recordings in early/budget digital cameras and cameraphones, and low-end smartphone screens. Original YouTube resolution. Maximum recommended size for "large" MMS videos.|
|SIF (525)||240p||352×240||84,480||4:3||NTSC-standard VCD / super-long-play DVD. Narrow/tall pixels.|
|NTSC widescreen||240p||426×240||102,240||16:9||Same as current YouTube "240p" mode; screen resolution of some budget portable DVD players. Roughly one-third full NTSC resolution (half vertical, two thirds horizontal).|
|CIF, SIF (625)||288p||384×288||101,376||4:3||PAL-standard VCD / super-long-play DVD. Wide/short pixels. Also a common resolution in early webcam / video conferencing, and in advanced featurephones and smartphones of mid-2000s (ca 2006).|
|PSP||272p||480×272||130,560||30:17||Notionally 16:9 with slight left/right edge cropping. Used in many portable DVD player screens and other small-format devices besides.|
|360p||360p||480×360||172,800||4:3||Uncommon, used in some lower-mid-market smartphone screens and as an intermediate screen resolution for some 1990s videogames.|
|nHD||360p||640×360||230,400||16:9||Current base resolution in YouTube, labelled as "360p".
The picture display on the Super Nintendo Entertainment System (Super NES) has two modes. One is an interlace mode, based on the television system. The other is a non-interlace mode, in which one frame takes 1/60th of a second. In the non-interlace mode the same position is scanned every field. Each frame consists of only 262 lines, half that of the interlace mode. There appears to be no flickering compared to the interlace mode, since each point on the screen is radiated every 1/60th of a second.