"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>...

> > "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,

[...]

> 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..."

The numbers given were for *horizontal* resolution maximums

(the vertical resolution limit is determined by the number of scan

lines, which is roughly 480 for NTSC for all formats - though

the "less able" formats may not approach this limit in practice

for on-screen resolution). On-screen resolution is a complex

issue - but it will always be at least a bit lower than the

theoretical maximum for the format (and often quite a bit lower,

which makes many Mini-DV camcorder manufacturers' claims

of "500-line resolution" for inexpensive 1-CCD models

"amusing"...;-)

--

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com