 A standard 4-pin S-Video male connector on a cable | |||
| Type | Analog video connector | ||
|---|---|---|---|
| Production history | |||
| Designed | 1987 | ||
| General specifications | |||
| Hot pluggable | Yes | ||
| External | Yes | ||
| Video signal | NTSC, PAL, or SECAM video | ||
| Pins | 4, 7, or 9 | ||
| Connector | Mini-DIN connector | ||
| Pinout | |||
 | |||
| Looking at the female connector. | |||
| Pin 1 | GND | Ground (Y) | |
| Pin 2 | GND | Ground (C) | |
| Pin 3 | Y | Intensity (Luminance) | |
| Pin 4 | C | Color (Chrominance) | |
| The shells should be connected together by an overall screen/shield. However, the shield is often absent in low-end cables, which can result in picture degradation. Same connector asApple Desktop Bus. | |||
S-Video (also known asseparate video,Y/C, and erroneouslySuper-Video)[1] is ananalog video signal format that carriesstandard-definition video, typically at525 lines or625 lines. It encodes videoluma andchrominance on two separate channels, achieving higher image quality thancomposite video which encodes all video information on one channel. It also eliminates several types of visual defects such asdot crawl which commonly occur with composite video. Although it is improved over composite video, S-Video has lower color resolution thancomponent video, which is encoded over three channels.[2]
TheAtari 800 was the first to introduce separate Chroma/Luma output in late 1979.[3] However, S-Video was not widely adopted untilJVC's introduction of theS-VHS (Super-VHS) format in 1987, which is why it is sometimes incorrectly referred to asSuper-Video.[4]
The S-video format was widely adopted in consumer equipment due to its improvements over composite video. However, it was rarely used by professional studios and broadcasters ascomponentYPbPr was superior for signal processing andstandard-definition TV was broadcast over NTSC composite signals.[5][6]
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Standardanalog television signals go through several processing steps on their way to being broadcast, each of which discards information and lowers the quality of the resulting images.
The image is originally captured inRGB form and then processed into three signals known asYPbPr. The first of these signals is calledY, which is created from all three original signals based on a formula that produces an overall brightness of the image, orluma. This signal closely matches a traditionalblack and white television signal and the Y/C method of encoding was key to offeringbackward compatibility. Once the Y signal is produced, it is subtracted from the blue signal to producePb and from the red signal to producePr. To recover the original RGB information for display, the signals are mixed with the Y to produce the original blue and red, and then the sum of those is mixed with the Y to recover the green.
A signal with three components is no easier to broadcast than the original three-signal RGB, so additional processing is required. The first step is to combine the Pb and Pr to form theC signal, forchrominance. The phase and amplitude of the signal represent the two original signals. This signal is thenbandwidth-limited to comply with requirements for broadcasting. The resulting Y and C signals are mixed together to producecomposite video. To play back composite video, the Y and C signals must be separated, and this is difficult to do without adding artifacts.
Each of these steps is subject to deliberate or unavoidable loss of quality. To retain that quality in the final image, it is desirable to eliminate as many of the encoding/decoding steps as possible. S-Video is an approach to this problem. It eliminates the final mixing of C with Y and subsequent separation at playback time.
The S-video cable carries video using two synchronized signal and ground pairs, termed Y and C. Y is theluma signal, which carries theluminance – or black-and-white – of the picture, including synchronization pulses. Y also carries horizontal and vertical sync pulses in the same way as acomposite video signal. C is thechroma signal, which carries thechrominance – or coloring-in – of the picture. This signal contains two color-difference components.
In composite video, the signals co-exist on different frequencies. To achieve this, the luminance signal must be low-pass filtered, dulling the image. As S-Video maintains the two as separate signals, such detrimental low-pass filtering for luminance is unnecessary, although the chrominance signal still has limited bandwidth relative to component video.[citation needed]
Carrying the color information as one signal means that the color has to be encoded in some way, typically in accord withNTSC,PAL, orSECAM, depending on the applicable local standard.
Compared withcomponent video, which carries the identical luminance signal but separates the color-difference signals into Cb/Pb and Cr/Pr, the color resolution of S-Video is limited by the modulation on asubcarrier frequency of either3.58 MHz (NTSC) or4.43 MHz (PAL). This difference is meaningless on home videotape systems, as the chrominance is already severely constrained by bothVHS andBetamax.
TheAtari 800 introduced separate Chroma/Luma output in late 1979. The signals were put on pin 1 and 5 of a 5-pin 180-degreeDIN connector socket. Atari did not sell a monitor for its 8-bit computer line, however.[3]
TheCommodore 64 released in 1982 (with the exception of the earliest revisions using a 5-pin video port) also offers separate chroma and luma signals using a different connector. AlthoughCommodore Business Machines did not use the termS-Video as the standard did not formally exist until 1987, a simple adapter connects the computer's LCA (luma-chroma-audio) 8-pin DIN socket to a S-Video display, or an S-Video device to the Commodore 1702 monitor's LCA jacks.[7]
The four-pinmini-DIN connector is the most common of several S-Video connector types. The same mini-DIN connector is used in theApple Desktop Bus for Macintosh computers. Apple Desktop Bus cables can be used for S-Video in a pinch.[8][9][10] Other connector variants include seven-pin lockingdub connectors used on many professional S-VHS machines, and dual Y and CBNC connectors, often used for S-Videopatch panels. Early Y/C video monitors often used phono (RCA connector) that were switchable between Y/C and composite video input. Though the connectors are different, the Y/C signals for all types are compatible.
The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of the pin breaking off.
These plugs are usually made to be plug-compatible with S-video, and include optional features, such ascomponent video using an adapter. They are not necessarily S-video, although they can be operated in that mode.
Non-standard 7-pin mini-DIN connectors (termed7P) are used in some computer equipment (PCs and Macs). A 7P socket accepts, and is pin compatible with, a standard 4-pin S-Video plug.[11] The three extra sockets may be used to supplycomposite (CVBS), an RGB or YPbPr video signal, or anI²C interface. Thepinout usage varies among manufacturers.[11][12] In some implementations, the remaining pin must be grounded to enable the composite output or disable the S-Video output.
Some Dell laptops have adigital audio output in a 7-pin socket.[13]
The 8-pin mini-DIN connector is used in someATI Radeon video cards[14]
9-pin connectors are used in graphics systems that feature the ability to input video as well as output it.[15][16] Again, there is no standardization between manufacturers as to which pin does what, and there are two known variants of the connector in use. As can be seen from the diagram above, although the S-Video signals are available on the corresponding pins, neither variant of the connector will accept an unmodified 4-pin S-Video plug, though they can be made to fit by removing the key from the plug. In the latter case, it becomes all too easy to misalign the plug when inserting it with consequent damage to the small pins.
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In many European countries, S-Video was less common because of the dominance ofSCART connectors, which were present on televisions until the advent ofHDMI. It is possible for a player to output S-Video over SCART, but televisions' SCART connectors are not always wired to accept it, and if not the display would show only a monochrome image.[17] In this case it is sometimes possible to modify the SCART adapter cable to allow full S-Video compatibility.
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