To understand this answer you need to know that a video signal is comprised of Luminance (brightness/contrast and sync, abbreviated to Y) and Chrominance (the three colours - Red, Green and Blue, abbreviated to C.) Composite: The lowest quality cable comprising a single copper or coaxial wire with either a phono, BNC or SCART connection. The Luma and Chroma signals are mixed and sent down the same cable leading to reduced image quality. S-Video: (Also known as Y/C) A single coaxial cable with a 4-pin mini DIN connection (but can also be integrated in a SCART cable). The Luma signal (Y) and Chroma signal (C) are separated and sent to different pins. They are recombined on input. This type of cable gives better quality than composite. Component: (Also known as Y U V, or Y Cr Cb) The best quality cable, comprising 3 copper or coaxial wires, generally with BNC connections (but can also be integrated in a SCART cable). The Luma is sent down one wire and the other wires contain the Red (Cr) and Blue (Cb) signals. The Green part of the signal is derived by subtracting the Red and Blue from the Luminance. This makes this type of connection the superior in terms of image quality.

There is also RGB also known as RGBHV (red green blue, horizontal, vertical). Typically you will find this used in VGA computer monitors. Unlike Component (where a difference is use for the green), the information for each colour is sent separately. Then for RGBHV the H and V are used to send the horizontal and vertical synchronization. RGB S, is where the synchronization is sent combining the V and H usually through pin 20 on a Scart adaptor. Typical RGB connections on a Scart are: 15 = red 11 = green or green with sync 7 = blue 20 = composite sync 2 = audio right 4 = audio ground 6 = audio left 16 = RGB mode select 8 = control switching You cannot easily convert from component to RGB. With Component you can connect the Y into a standard composite (yellow) input, and you will see receive a black and white picture. If you try the same thing with a colour from RGB you wont see anything with out also connecting the sync. If you have the choice, RGB is the best, then Component, then S-video, then Composite. Note that all for may be possible through a single Scart connection.