is this true? resolution myths?

[ronnylov]

All this talk of horisontal lines of resolution and pixels and oversampling is a little bit confusing. But I found this link:
http://members.aol.com/ajaynejr/vidres.htm

They talk about the circular rule. Quote from this link:
"When measuring "lines of resolution" for TV sets or monitors, a reference distance needs to be specified. Traditionally, video resolution is measured across the largest circle (not an ellipse) that fits in the space we are talking about. All the technical books on video say this, although using different words. On a standard TV screen such a circle would span 3/4 of the screen width. For U.S. HDTV (16:9 aspect ratio) the circle would span a little over half the screen width. Since the circle exactly fits the screen height (assuming no overscan), the phrase "picture height" stands for a distance equal to the diameter of the circle and is also used when talking about horizontal resolution. The circle rule also applies to film.

Under this rule, if a standard (4:3) TV set can reproduce 800 dots alternating black and white across the screen width using an input signal representing same, it is said to have 600 lines of horizontal resolution. However if the source material had just 330 lines of resolution you will see just 330 lines of resolution. A 16:9 aspect ratio TV that can reproduce just 800 dots across its screen would have 450 lines of horizontal resolution."
End of quote.

Should I interpret this as if VHS has 240 lines of reolution this would correspond to 240*4/3= 320 dots of alternating black and white across the screen on a traditional 4:3 TV? So even if I capture at a higher resolution the real resolution is not higher. But some sources can have "over 500 lines of resolution" (like DVD-players). This would correspond to over 667 dots of alternating black and white. This sound correct because if you count the overscan area this may leave around 670 "visible pixels of horisontal resolution".

I also found this link:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/750

The table is a good reference. There also some formulas and stuff.

Then we had the original question of the capturing via S-VIDEO cable. If somebody could tell the bandwidth of this cable connection we could calculate what resolution it corresponds to. If it's higher than the bandwidth of the video source then the source is the limiting factor.

Since the table show that NTSC maximum limit is 338 lines of vertical resolution and 451 horisontal active pixels it seems that half D1 destination resolution is not enough to get all the details from the broadcast. SVCD resolution seems to be enough. But if your destination is DVD then you can't choose anything between 704 and 352 so 704 pixels horisontal resolution seems to be the right choice. But all sources are not of maximum quality. VHS source is fine also with half D1 resolution on the final destination format because maximum VHS resolution is 240 lines, which would correspond to 320 "pixels of visible horisontal resolution".

PAL maximum limit gives 403 lines of hor. res. and 538 "total horisontal active pixels". So you need to capture with higher resolution than 538x576. 704x576 seems to be a good choise as both capture and destination format.

I'm not sure how the overscan area should be taken into account. Maybe 480x480 is what you need for full NTSC and 576x576 for full PAL broadcast quality? Anyway the conclusion is the same - 704 pixels of horisontal capture resolution should be enough but half D1 may not show all the details of the original broadcast.

But if VHS-like resolution is good enough for your liking, then by all means choose the half-D1 DVD format as destination.

EDIT: I have read the original post again and he claims that S-VIDEO connection in theory removes 1/5 of the NTSC bandwidth. If that is true then you may end up with 384x480 just like he said. Then analogue video capture in NTSC is not much better than VHS recordings? I normally capture PAL video so that may be the reason I find that half-D1 is worse than full D1 from my analogue captures?