"Dave
Haynie" <dhaynie@jersey.net> wrote in message
news:404f8761.2022870203@news.jersey.net...
> On
Mon, 08 Mar 2004 20:44:19 GMT, "David Ruether"
>
<rpn1@no-junk.cornell.edu> wrote:
>
>>"Michael J. Hennebry" <hennebry@web.cs.ndsu.nodak.edu>
>
>wrote in message news:99a0b764.0403080742.2a2c5c4b@posting.google.com...
>
>> "David Ruether" <rpn1@no-junk.cornell.edu> wrote in
message
>
>news:<OtG1c.26466$6c5.14743@nwrdny01.gnilink.net>...
>
>> If VHS only produces 240 lines out of 540 and still fills most
>
>> of the screen, that suggests a tremendous vertical overscan.
>
>> I'd read that TVs generally have a rather large horizontal
>
>> overscan, but not that much.
>
>> I expect that I'm missing something, but obviously I don't
>
>> know what.
>
>"The horizontal number determines the horizontal resolution..."
>
What's confusing you [the original poster...;-] is the definition of
"lines".
>
>
David here is talking about about "lines of resolution", in the pure
>
optical sense. That's an analog measure, from ages past, of the
>
resolving accuracy of any optical system. This takes place in a
>
perfect circle (by convention) within your focal plane or image field.
>
>
For NTSC video, you are guaranteed a real 480 lines horizontally.
>
Maybe 484 if you're doing analog, but that's not germaine. The number
> of
horizontal lines is not subject to debate, it's "of a digital
>
nature", eg, it's discrete, even in analog systems.
>
>
For vertical lines (eg, along the horizontal scan line), however, you
>
have an analog function. There are no pixels, only transitions. This
> is
why commercial digital titlers for analog video often work in 1400
> or
2000+ pixels. Video can't resolve anything close to 2000 horizontal
>
pixels (vertical lines), but any old analog system can resolve
>
transisions with 2000-pixel accuracy, as long as they're far enough
>
apart from one another. But I yet-again digress.
>
>
Anyway, onto digital. That perfect circle you draw into a video frame,
>
limiting the horixontal dimension, based on aspect ratio, to the same
>
visual length as the vertical dimension, is the basis for video "lines
> of
resolution". Given that DV is digital, there's no analog aspect at
>
all. You get 720 pixels across. In that perfect circle, that means you
>
get 540 pixels in the circle for 4:3, 405 pixels in the circle for
>
16:9. Of course, those single pixels at the edges don't really make
>
lines, so it's a bit of a fudge factor between this mathematical
>
number, and what you'll ever see on a resolution chart shot through
>
your camcorder viewfinder.
>
> If
you speak of VHS, a properly measured "lines of resolution" along
>
the horizontal (eg, vertical lines) is, very much, a normal analog
>
measure, within that perfecly inscribed 4:3 circle. People confuse
>
that with pixels, because it's 2004 and it's natural to want to
>
compare to DV or DVD. But it's not even related to pixels.
>
>
>
Dave Haynie | Chief Toady, Frog
Pond Media Consulting
>
dhaynie@jersey.net| Take Back Freedom! Bush no more in 2004!
>
"Deathbed Vigil" now on DVD! See http://www.frogpondmedia.com
Thanks
for this excellent exposition on a topic that confuses many.
--
David Ruether
d_ruether@hotmail.com
http://www.David-Ruether-Photography.com