Engineering:Low-definition television

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Short description: TV systems with screen resolution lower than standard-definition


Low-definition television (LDTV) refers to TV 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 television systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan television systems.

Sources

The Video CD format uses a progressive scan LDTV signal[citation needed] (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 256x144 or 144p at 30~50 fps 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,[1] 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.

Video games

Older video game consoles and home computers often generated a technically compliant analog 525-line NTSC or 625-line PAL signal, but only sent one field type rather than alternating between the two. This created a 262 or 312 line progressive scan signal (with half the vertical resolution), which in theory can be decoded on any receiver that can decode normal, interlaced signals.[2][3][4][5]

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 introduction of digital video formats these low-definition modes are usually referred to as 240p and 288p (with the standard definition modes being 480i and 576i).

With the introduction of 16-bit computers in the mid-1980s, such as the Atari ST and Amiga, followed by 16-bit consoles in the late 1980s and early 1990s, like the Sega Genesis and Super NES,[4] outputting the standard interlaced resolutions was 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, progressive output with half the vertical 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, standard interlaced resolution became more common, and progressive lower resolution 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'.[6][7]

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,[8] however many games released prior were never updated.[9]

Teleconferencing LDTV

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.[citation needed]

Resolutions

Standard Class Resolution Pixels Aspect Ratio Notes
MMS-Small 96p 128×96
QQVGA 120p 160×120 Template:Multiply 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
144p 144p 192×144 4:3 The resolution 192×144 is used when 144p is selected on a fullscreen YouTube video.[citation needed]
YouTube 144p 144p 256×144 Template:Multiply 16:9 One tenth of 1440p. The lowest resolution on YouTube.
QnHD 180p 320×180 16:9
222p 222p 400×222
QVGA, NTSC square pixel 240p 320×240 Template:Multiply 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 Template:Multiply SAR 22:15 / DAR 4:3 NTSC-standard VCD / super-long-play DVD. Narrow/tall pixels.
NTSC widescreen 240p 426×240
CIF / SIF (625) 288p 352×288 101,376 SAR 11:9 / DAR 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)[citation needed].
Widescreen CIF 288p 512×288 Template:Multiply 16:9 Widescreen version of 288p resolution
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
QuickTime File Format 320p 568×320
nHD 360p 640×360
  • The lowest and least computationally demanding resolution supported by hardware able to run mainstream desktop operating systems;[vague] the lowest interruption-free resolution with low-end broadband connections.
  • Typically used as the base "SD" standard by VoD services due to subjective similarity (and similar pixel counts) to a mid-grade free-to-air broadcast picture.
  • Effectively, the resolution offered by any higher-definition 16:9 video scaled down for a standard 640×480 (VGA) computer screen. Offers 75% of the pixel count of a true anamorphic NTSC DVD image, or 89% of a letterboxed 16:9 image.
  • Historically used as an ad-hoc standard for intermediate-quality / CD-R-sized MPEG4 conversions on P2P file sharing networks.

See also

References

  1. ↑ Robertson, Mark. "What Is This 144p Stuff, YouTube?". ubular Insights & Tubular Labs, Inc.. https://tubularinsights.com/144p-stuff-youtube/. 
  2. ↑ "Scanlines Demystified". http://scanlines.hazard-city.de/. 
  3. ↑ "Connecting your old videogames to your new flatpanel TV set". http://retrogaming.hazard-city.de/. 
  4. ↑ 4.0 4.1 SNES Development Manual. Nintendo of America. 1993. p. 2-1-2. https://archive.org/stream/SNESDevManual/book1#page/n59/mode/1up. Retrieved 2017-08-28. "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." 
  5. ↑ Hinner, Martin. "PAL video timing specification". http://martin.hinner.info/vga/pal.html. 
  6. ↑ "N64 Functions Reference Manual - Video Interface (VI) Management". http://naesten.dyndns.org:8080/psyq/man/os/osVi.html. 
  7. ↑ "GameCube SDK - Video Interface Library (VI)". p. 6. http://www.djek.nl/Downloads/GC/DOCS/GRAPPRO/VI.us.pdf. 
  8. ↑ "Nintendo Support - Display problems while playing Virtual Console games". https://www.nintendo.com/consumer/systems/wii/en_na/ts/pictureSound.jsp#neogeo. 
  9. ↑ "Wii Component cable Interlace Mode". http://forums.computerandvideogames.com/viewtopic.php?t=32854. 



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