"Michael J. Hennebry" <hennebry@web.cs.ndsu.nodak.edu>

wrote in message news:99a0b764.0403150803.36b2edfc@posting.google.com...

> Thanks folks for all the replies.

> Please let me know if I've understood them correctly.

I think this all has been covered before, but....

> I'm assuming a situation in which the post-camera processing matters,

> i.e. one in which there is an electronic image with 480 lines of

> vertical resolution available.

>

> What shows up on a TV screen might have less than 480 lines of

> vertical resolution because at some point a horizontal line of a field

> suffers averaging with adjacent lines within the same field.

>

> In the case of VCRs, said averaging occurs because of the physical

> overlap of the magnetic stripes representing the lines.

>

> A low-resolution original is not the only other reason for less than

> 480 lines of vertical resolution.

> I'm not clear on what other reasons there are.

You are mistaking image-origin resolution with TV resolution, - but

the displayed TV image is analogue (but with a fixed number of

available scan lines and an unspecified maximum resolution in the

other direction - which is determined by an interaction between

display capability, source resolution, format resolution, and playback

device capability...). The final display resolution may (under VERY

ideal conditions) be a near match for the original, or be FAR from it.

> How many lines of vertical resolution do we normally get from

> broadcast? cable? cable copies of broadcast?

Roughly (and these are MAXIMUMS for horizontal TV lines,

never really achieved), as I recall (with vertical TV lines = about

480 lines NTSC with all): VHS - 240; broadcast, 340; Hi-8/SVHS,

maybe 400+; DVD, 440(?), D25, 540 - BUT, given the variables

above, the best VHS can look better than so-so D25, so these

figures guarantee very little...

Again, the best input, combined with the best processing and

the best displays, will produce the best results, but MUCH

can modify/degrade the outcome!

--

David Ruether

d_ruether@hotmail.com

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