Trying to wrap your head around something as outwardly simple as 'the difference between RGB and composite or S-video' shouldn't involve hours of research and dozens of diagrams and examples. It shouldn't involve research into human vision deficiencies, our inability to percieve details in colour, or obscure photographic terminology either. And yet it does - all this and more.
A quick background on TVs is required, please bear with me. A TV (And this is the same for arcade monitors) is made of two basic components: A vacuum tube and some supporting electronics (called the chassis). There's an electro-magnet around the tube, and some electron emitters in the back. By spraying electrons at the front of the tube an image is produced. The chassis controls how many electrons the emitters spew out (brightness), and by controlling the magnets on the tube the direction of the electron spray is controlled (location). By sweeping the electron stream back, forth, up and down very quickly an image is produced on the front of the tube, which is what we see. In the early days of TVs there was only one emitter (or gun) in the back of a monitor, and all images were black and white, or greyscale. Naturally this didn't satisfy for long and a method for creating colour images was needed, and here's where it gets interesting. By using three guns (one for Red, Green and Blue) as well as a more complicated tube assembly all the colours of the rainbow could be produced. This introduced a new problem, however: Governments allowed only a certain amount of bandwidth to each channel, and three colours required triple the bandwidth. And what about older TVs that could be confused by the new signal data? So they took the black and white signal and slapped a colour signal on top of it. By this I mean the black and white signal was unchanged, and the colour signal was a simple chrominance, or hue, indicator. Don't worry if that's not quite clear (And for that I apologize), it's not important. What is important is that they didn't keep the same resolution for the colour signal. In order to minimize the bandwidth they kept the colour resolution much smaller than the black and white resolution - approximately one third, in fact. This was a shocking realization to me, and I imagine it should be to you too. Every time you use your AV cables, which used to look so clear, you're getting a high-res black and white signal and a low-res colour signal. S-Video is the same, to a lesser extent, and component video is the same as well, kind of, depending on a lot of variables. And this is why the story's so tricky: You've got a standard built on top of another standard designed to use less 'airspace' so that you could have more channels on a TV. It had to be cheap, small, and work on existing systems. It's amazing it works at all, but from a quality point of view it was practically designed to suck.
And that's our TV history, that's how we got from there to here, but so what? What's this got to do with RGB and game consoles? How bad is it really? Well I'm gonna show you how bad. For years I've been screaming the benefits of RGB from the mountain top (molehill, but whatever) of gamesx.com and more recently AtariLabs.com, but I was basing this comment of superiority on the clarity of the RGB signal. I never fully realized until recently that the colour resolution was so appallingly low. Here come the visual aids. Have a look at this screenshot from Capcom's Saturn version of Street Fighter Alpha 2: 
Pass your mouse over the image to change RGB to Composite. What you see above is the identical image at first and, when you pass your mouse over it, the same image with a 1/3 horizontal colour resolution. |