S-video

OVERVIEW

The Luminance (Y; brightness) signal and Modulated Chrominance (C; colour) Subcarrier information are carried on separate synchronized signal/ground pairs.

In Composite Video , the luminance signal is Low-pass Filter ed to prevent Crosstalk between high- Frequency luminance information and the color subcarrier. S-Video separates the two, and detrimental low-pass filtering is unnecessary. This increases Bandwidth for the luminance information, and also subdues the color crosstalk problem. The infamous Dot Crawl is eliminated. This means that S-Video leaves more information from the original video intact, thus having a much-improved image reproduction compared to composite video.

Due to the separation of the video into brightness and colour components, S-Video is sometimes considered a type of Component Video signal, although it is also the most inferior of them, quality-wise, being far surpassed by the more complex component video schemes (like RGB ). What differentiates S-Video from these higher component video schemes is that S-Video carries the colour information as one signal. This means that the colours have to be encoded in some way, and as such NTSC , PAL and SECAM signals are all decidedly different through S-Video. Thus, for full compatibility the used devices not only have to be S-Video compatible but also compatible in terms of colour encoding.

CONNECTOR

Today, S-Video signals are generally connected using 4-pin mini- DIN connectors using a 75 Ohm termination impedance. Apart from the impedance requirement, these connectors are identical to ones used for the now-obsolete Apple Desktop Bus ; ADB cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good, and there is a risk of damage to unshielded Cathode Ray Tube s via incompatible Resistances .

The pins in the connector are bent rather easily, but this can be prevented using care when properly inserting the connector to the receptacle. If a pin is bent, the result could be the loss of colour, or other corruption (or loss) of the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off.

Before the mini-DIN plug became standard, S-Video signals were often carried through different types of plugs. For example, the Commodore 64 Home Computer of the 1980s , one of the first widely available devices to feature S-Video output, used an 8-pin standard size DIN plug on the computer end and a pair of RCA plugs on the monitor end. The S-Video connector is the most common video-out connector on laptop computers, however many devices with S-Video outputs also have composite outputs.

Today, S-Video can be transferred through SCART connections as well. However, it was not part of the original SCART standard, and not every SCART-compatible device supports it for this reason. Also, S-Video and RGB are mutually exclusive through SCART, due to the S-Video implementation using the pins allocated for RGB. Most SCART-equipped televisions or VCR s (and almost all of the older ones) do not actually support S-Video, resulting in a black-and-white picture if attempted to use, as only the luminance signal portion is used. Black-and-white picture in itself can also be a sign of incompatible colour encoding, for example NTSC material viewed through a PAL-only device.

A hack exists to possibly attain color on devices that do not support S-Video through SCART. This is done via joining the pins 15 and 20 in the SCART connector (either directly or using a 470pF capacitor), and may not yield optimal results.

USAGE

S-Video is commonly used in USA, Canada, and Japan, found there on consumer TVs , DVD Player s, Video Tape Recorder s and Game Console s. Almost all TV-out connectors on Graphics Card s are S-Video, even in Europe, where the standard failed to make a significant impact due to the preference of the higher-quality RGB signal.

Some particularly cheap S-Video cables are notorious for degrading the signals considerably, when transmitted across more than 5 meters.

Because it is very simple to convert S-Video to composite signal (just the logical merging of the two through a filter is required) or vice versa, many electronics retailers offer converter adaptors for signal conversion. Obviously, no conversion will improve image quality, but will allow connecting to otherwise-incompatible devices.

S-Video does not carry audio. Hence, a separate audio connection is required.

SEE ALSO

REFERENCES

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S-video