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Low-definition television (LDTV) refers toTV systems that have a lowerscreen resolution thanstandard-definition television systems. The term is usually used in reference todigital television, in particular whenbroadcasting at the same (or similar) resolution as low-definitionanalog television systems.Mobile DTV systems usually transmit in low definition, as do allslow-scan television systems.
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TheVideo CD format uses aprogressive scan LDTV signal[citation needed] (352×240 or 352×288), which is half the vertical and horizontal resolution of full-bandwidthSDTV. 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 30frames per second, and the resultant display is comparable to consumer-gradeVHS 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 byGoogle, 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 usingRealVideo or similar services, where 160×120 at single-figure framerates was deemed acceptable to cater to those whose network connections could not sufficiently deliver 240p content.
Oldervideo game consoles and home computers often generated a technically compliant analog525-lineNTSC or625-linePAL 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 theshadow mask and beam width of standardCRT televisions were designed for interlaced signals, these systems produced a distinctive fixed pattern of alternating bright and darkscan lines; manyemulators for older systems offer video filters to recreate this effect. With the introduction ofdigital video formats these low-definition modes are usually referred to as 240p and 288p (with the standard definition modes being480i and576i).[6]
With the introduction of 16-bit computers in the mid-1980s, such as theAtari ST andAmiga, followed by 16-bit consoles in the late 1980s and early 1990s, like theSega Genesis andSuper 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 thefourth andfifth generation consoles (including the Sega Saturn, the Sony PlayStation and the Nintendo 64).[7][8][9]
With the advent ofsixth generation consoles and the launch of theDreamcast, 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. ThePlayStation 2 generates 240p/288p if a PlayStation game calls for this mode, as do manyVirtual Console emulated games on theNintendo Wii. Nintendo's officialsoftware development kit documentation for the Wii refers to 240p as 'non-interlaced mode' or 'double-strike'.[6][9][10]
Shortly after the launch of the Wii Virtual Console service, many users withcomponent 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,[11] however many games released prior were never updated.[12]
Sources of LDTV using standard broadcasting techniques include mobile TV services powered byDVB-H,1seg,DMB, orATSC-M/H. However, this kind of LDTV transmission technology is based on existent LDTVteleconferencing standards that have been in place since the late 1990s.[citation needed]
| Standard | Class | Resolution | Pixels | Aspect ratio | Notes |
|---|---|---|---|---|---|
| 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.[citation needed] |
| 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 | SAR 11:9 /DAR 4:3 | Approximately one-sixth analogue PAL resolution (one-half horizontal, one-third vertical).[citation needed] Also the size recommended for "medium" quality MMS videos.[citation needed] |
| 144p | 144p | 192×144 | 27,648 | 4:3 | The resolution 192×144 is used when 144p is selected on a fullscreen YouTube video.[citation needed] |
| YouTube 144p | 144p | 256×144 | 36,864 | 16:9 | One tenth of 1440p. The lowest resolution on YouTube since 2013.[13] |
| QnHD | 180p | 320×180 | 57,600 | 16:9 | |
| 222p | 222p | 400×222 | 88,800 | 16:9 | Used in low-resolutionFacebook widescreen videos.[citation needed] |
| 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 | SAR 22:15 / DAR 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).[citation needed] |
| 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] |
| WidescreenCIF | 288p | 512×288 | 147,456 | 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 | 172,800 | 4:3 | Uncommon, used in some lower-mid-market smartphone screens and as an intermediate screen resolution for some 1990s videogames.[citation needed] |
| QuickTime File Format | 320p | 568×320 | 181,760 | 16:9 | Used for .MOV files recorded withiPhone cameras.[citation needed] |
| nHD | 360p | 640×360 | 230,400 | 16:9 | Current base resolution in YouTube, labelled as "360p".[citation needed]
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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.
