Quality difference between S-video and RCA

Question

Can someone tell me what's the difference (in quality) between S-video out and RCA out?
I'm using RCA out because with s-video, the image shows up in black and white on my TV.
It would help to know I'm not loosing too much quality this way...
Regards everyone.

Answer 1

pauliewog is speechless  
But what Robi says is true!
The various forms of (analogue) signal transfer are, in descending order of quality:
RGB - The Red, Green and Blue signals are generated by the PC (say), and connected by separate wires to ultimately control the Red, Green and Blue electron guns of the display monitor/TV set. The standard 15-pin "VGA" connector is RGB (plus H and V synchronising pulses).
YUV - Also called Component, and YCrCb, as found on DVD players. The Y is the luminance, or Black-and-White component, while the Cr and Cb are the Differences between the Y and the Red and Blue signals respectively. Usually, the Y signal has higher bandwidth than the Cr and Cb signals (twice as many Y samples as Cr and Cb samples on the DVD). Still needs wires, but the Sync is added to the Y signal.
Y/C - aka S-Video. The Y is as above, but the Cr and Cb signals are used to modulate a subcarrier (3.579545MHz for NTSC, 4.43361875MHz for PAL), with one of the signals effectively at 90 degrees to the other - the C signal. The bandwidths of the colour difference signals need to be bandwidth limited to about 1/3 of the subcarrier frequency (about 1.7MHz for PAL from memory), compared to the Y bandwidth of 5MHz for broadcast television. In PAL, the phase of one of the signals is inverted every other line (PAL = Phase Alternating Line, aka Peace At Last). Transmission errors which result in green faces and purple trees in NTSC (National Television Standards Commitee, aka Never Twice the Same Colour) tend to desaturate the colours instead.
CVBS, aka Composite Video (also RCA, named after the company that developed the type of connector used, which is typically yellow for video). The Y and C (and sync) signals are combined one one wire. The TV has a harder job of separating them back to RGB  :(
RF (Radio Frequency). The CVBS signal is modulated onto an RF carrier, which could be anywhere between about 45MHz and about 1000MHz (not counting satellite distribution), so that it looks the same as a broadcast TV station to a TV set, and connects via a single cable to the antenna socket of a TV set. So first the TV has to demodulate the signal back to CVBS, before separating the Y and C, then separating the C into Cr and Cb and putting into a matrix with the Y to get RGB back. Nevertheless, this is a useful technique for distributing a signal to a lot of TV sets over a reasonably large area. It is also the only method that works with old TVs without A/V inputs - which is why game consoles used to come with an RF Modulator (aka RF Converter) as standard.
The above methods are also in descending order of signal bandwidth, which restricts the available resolution, or the finest horizontal detail (especially colour detail). Generally, 800x600 is about as good a resolution as you can expect to get on a TV display without resorting to special enhancing techniques.
The above is probably a lot more detail than you need, but is still a fairly superficial explanation. But study it up, the test is next Monday at 9am  :D
Cheers