S-video
S-Video (also known as Separate Video , Y / C ) describes the separate transmission of brightness ( luminance ) and color ( chrominance ) information via appropriately designed cables and plug connections . It enables better quality signals than composite video , especially when used in inexpensive devices, but does not achieve the quality of RGB signals or component video .
S-Video is often mistakenly equated with the S-VHS ( Super Video Home System ) video recording format. The connection is also similar to the PS / 2 interface .
description
The brightness signal and the modulated color carrier are transmitted via two separate signal / ground line pairs. The brightness signal (Y) also contains synchronization signals , so it is a black and white television signal (BAS). The color signal (C) is modulated in the manner corresponding to the underlying television standard (with PAL, for example, with quadrature modulation ), but not mixed with the brightness signal (as with FBAS / composite video ), but transmitted via a second connecting wire.
In contrast to composite video, S-Video does not require a chrominance filter in the receiver that would have to separate the color signal from the brightness signal. This not only avoids cross-luminance and cross-color interference, but also enables broadband video signals in practice. The gain in horizontal resolution makes details more visible.
It is also possible to increase the transmission bandwidth of the color signal, but this is rarely used in practice.
Technical details
S-Video is not a video format . Rather, the corresponding baseband analog television standard is used as a basis. Depending on the CCIR transmission standard, the brightness and color signal occupy different frequencies.
For the PAL format commonly used in Germany , the color signal is transmitted at 4.43361875 MHz, as is the case with FBAS / composite video. The bandwidth of the chrominance modulation is nominally approximately ± 1.3 MHz.
Composite video adapter
In order to benefit from the advantages of this type of connection, S-Video should only be used between S-Video-compatible devices. However, especially in the home, it can happen that you want to feed a composite video device with S-Video (e.g. notebook on television).
The S-Video signal can be returned to a composite / FBAS signal by filtering the luminance signal (bandstop on the color carrier with a bandwidth that does justice to the color signal) and adding it to the chrominance signal.
Simple S-Video to composite adapter only use the luminance signal of the S-Video connection. Since both video signals are transmitted at 75 ohms each, this is possible without any problems (when using a 75-ohm cable). However, only a B / W signal is then available at the composite output of such an adapter . If the luminance signal is not band-limited accordingly, chrominance artifacts can occur due to the missing filter .
A very simple circuit that can mix in the color component combines the luminance (Y) and chrominance signals (C) via a 470 pF capacitor and picks up a “composite” signal at the Y pin. A sufficiently good color image is obtained (the transmission and reflection properties, especially the supply of the chrominance input, are worthy of criticism). Here, too, the actually necessary filtering of the luminance signal is missing. This circuit cannot be used in the opposite direction (from composite to S-video); active components are required for this.
plug
Nowadays, S-video signals are generally transmitted via 4-pin mini-DIN connectors (also known as Hosiden connectors ) with a terminating resistance of 75 ohms. The pins in the plug bend easily, so plugging in requires caution. If a pen is bent, it will cause color loss, corruption, or loss of the signal.
Sometimes mini-DIN plugs with more than 4 poles are used for S-Video. In this case there are also the usual S-Video signals on the pins that are in the usual positions of the 4-pin connector. B. contain composite, RGB and / or component signals. Such solutions were sometimes found on PC graphics cards, because there was not enough space on the rear panel to accommodate two PC monitor connections and several TV sockets. These solutions were manufacturer-specific and required the use of an adapter cable supplied or purchased separately from the manufacturer if signal forms other than S-Video were to be used. For use as an S-Video socket, on the other hand, standard cables could be used, the plugs of which then simply did not contact all the pins of the socket.
Before mini-DIN became standard, different connector shapes were used for S-Video. For example, the home computer Commodore 64 (1980s), which was one of the first mass-produced devices to output S-video signals, used an 8-pin DIN plug on the computer and a pair of cinch plugs on the monitor.
Today the S-video signal can also be transmitted via SCART connector . However, the input concerned must explicitly support S-Video, as it is not part of the SCART standard. In addition, the simultaneous support of RGB and S-Video signals via a single SCART socket is difficult in terms of circuit technology, as there are too few lines for this. Most televisions with two SCART sockets can both be fed with composite video, but only one of the two processes RGB or S-video. If there is only one SCART socket on the device, it almost always accepts composite and RGB, but not always S-Video. Unlike switching between composite and RGB signals, which with SCART can be automatically signaled by the sending device (e.g. DVD player) to the receiving device (e.g. TV) via a line reserved for this purpose, the Switching between composite and S-video signals can almost always be done manually on the receiving device, as SCART does not provide a signal line for this.
use
S-Video is commonly used in home DVD devices and VCRs. It is also sometimes used in professional technology, such as computer video cards , but in the computer sector it has been largely pushed back by newer digital connection forms such as DVI, HDMI and DisplayPort. In Europe, S-Video was not previously widespread, as RGB signals were mostly used there via SCART sockets. In the USA, where SCART sockets are almost unknown, S-Video was and is the most widely used connection type for high-quality television and video components. S-Video is now one of the common standards in Europe too.
