"rick
cameron" <rick.cameron@tee ee el you ess dot en ee tee> wrote in
message news:noA1c.66318$A12.8417@edtnps84...
>
"David Ruether" <rpn1@no-junk.cornell.edu> wrote in message
>
news:LAx1c.23523$6c5.16111@nwrdny01.gnilink.net...
>
> "Michael J. Hennebry" <hennebry@web.cs.ndsu.nodak.edu>
>
> wrote in message news:99a0b764.0403031409.20c0e0a2@posting.google.com...
>
> > Are the pixels square?
>
> > If so, 720:480 = 3:2.
>
> > What uses 3:2?
>
> The vertical number is determined by the number of NTSC TV
>
> scan lines, and is fixed; the horizontal number determines the
>
> horizontal resolution (using rectangular pixels to maintain the
>
> 4:3 picture proportion), and "everything comes out right"
>
> when the image is converted to an analogue signal for the TV.
>
> --
>
> David Ruether
>
That explains the 480, but not the 720.
>
Any idea who chose 720 as the horizontal resolution, and why?
> -
rick
"The
horizontal number determines the horizontal resolution
(using
rectangular pixels to maintain the 4:3 picture proportion)."
The
horizontal number is a fixed part of the DV standard for
D25
format. It could have been anything (higher would have
delivered
higher possible horizontal resolution), but selecting
a
higher value would have required more compression or
a
higher data rate. Given the general characteristics of SD
NTSC
TV, it would likely rarely provide much (or any)
noticeable
improvement in the TV-viewed image. It takes
large
resolution improvements to show noticeable image
resolution
improvement - which is why lowly VHS at
240
lines and broadcast at 340 lines (maximum!) can still
look
good on a good TV, but even 540 lines (maximum,
rarely
achieved, and not often closely-approached in
practice)
for D25 often doesn't look much better (or
often
even as good, depending on source characteristics)
than
the image from much lower resolution formats.
720
horizontal pixels was a reasonable
choice given the
vertical-line
resolution limit built into NTSC, the average
resolution
capabilities of most TVs, and the
requirements
for
reasonable compression and data rates.
720
offers the potential for some improvement over past
formats
like VHS, SVHS, 8mm, Hi-8, BetaSP, and
broadcast
- but most of the time even this potential
improvement
is not seen...
--
David Ruether
d_ruether@hotmail.com
http://www.David-Ruether-Photography.com