Video signals, fomats and progressive scan (?)

[Cranberry]

I have been helping a couple of friends set up their DVD / Hi-fi systems and they've asked some questions that I couldn't answer. Does anyone know:
- How come older TVs manage to cope with RGB output for R1 discs? What difference does this make over RF?
- What's the difference between RGB and S-VHS? I've assumed that RGB sends a red, green and blue signal but don't know much about S-video
- What's progressive scan?

I'm sure some of these questions have been asked before... would it be worth having a 'basics' sticky?

[Chris]

1) RGB is neither PAL or NTSC, it only has the line structure and frame rate of the source format. RGB bypasses the colour circuits etc of a tv, with older tvs RGB tends to go directly to the tube. Some newer tvs allow some control of the RGB signal (brightness etc) by processing the RGB signal just before sending it to the tube.



3) DVD, TV etc is interlaced video, this is where the odd lines of the screen are drawn then the even lines are drawn (this halves the requires bandwidth for broadcasts). With PAL video it's done so quickly (25 frames per second, 2 fields (one odd, one even) make up each frame, so it has a frequency 50Hz) to avoid flicker (flicker can be noticed by some and if bright light shines on the tv, thats why 100Hz tvs came out). With DVD Players that have progressive scan support they process the interlaced video on dvd, if it was mastered from a progressive source (odd and even frame drawn at same time) the player can recombine the fields in to one full frame. (produces a rock solid image that it easier to imcrease the refresh rate without affecting picture quality) To use progressive you need a dvd player AND display (some hi-end tvs, some plasma screen, some projectors). Currently progressive support is only available with NTSC video.

[Cranberry]

Chris - thanks for the info.... has cleared a lot of things up. One question - is progressive scan still 25 frames per second?