Video Conversion seems like it should be very easy to do to the average person. People often think it is a matter of just connecting the proper input wires together in away that the proper signals are all together on the proper output wires. This would, in fact, be very wrong.
The biggest problems in converting between signals is due to the way in which the color and brightness signals are encoded. This encoding of the signals makes simply connecting wires impossible.
Taking a "simple" signal like Composite and converting it to a superior signal format like a Component signal, or vice versa, is actually rather complex. Listing the steps involved in converting from Composite video to Y-Pr-Pb Component video would make any normal persons head spin. The newer encoding schemes progressively take more advantage of how well the human eye perceives brightness (black and white) and color details.
OK, so we're saying it's, like, tricky.
Composite video: That RCA connector Cable with the yellow color code. It combines the brightness (luminance) of the picture elements with their associated color (chrominance) information all on a single coax cable. Many hoops were jumped through to get all of the original red, green, blue and brightness information onto, essentially, a single signal.
S-Video: S-Video separates the brightness and color signals improving both signals ability to provide more detail.
RGB/VGA: RGB allows for Completely separate red, green and blue video element information. Brightness is basically the overall sum of the three Color signal brightness levels. RGB is inefficient, since lots of redundant signal is passed on the three connections.
Component Video (Y-Pr-Pb) :Component video can actually mean a number of things, but is most associated with Y-Pr-Pb analog signals. Y-Pr-Pb encoding takes better advantage of available space and bandwidth on the video recording medium and cables, respectively. It is not compatible with RGB despite using Red, Green and Blue color coded connectors.
-> Methods of Conversion you should understand:
Transcoding: Changes the signal encoding, from RGB to Y-Pr-Pb, for example, but does not convert the signal in any other way. Resolution, aspect ratio and other factors remain the same.
Conversion: Converts encoding and Signal format but not usually resolution, unless it has scaling capabilities. Converters with Scaling can adjust the input signal to fit the resolution and aspect ratio of the screen.
A) The main thing is to know what you have for an input signal and want for an output signal before you begin. If you need Composite or S-video input or output, then that part is easy - use a converter with composite NTSC or PAL input or output to match what you need. You just need to know what you want on the other end. With RGB/VGA going to/from Component video (Y-Pr-Pb) you have to know the input and output resolutions and signal types (interlaced or progressive) before choosing an appropriate Transcoder, Converter, or Converter/Scaler.
B) Video Conversion always has an effect on your signal quality. The less conversions you do, the better off you will be.
C) Quality of the Electronics can have a very large effect on the ultimate signal quality. Since, conversion is NOT, a simple thing.