[mythtv-users] What Resolution Are You Using?

[Bruce Markey]

jasonmiller wrote:
> Technically NTSC is 320x240, PAL is 320x288.

Well, technically NTSC is analog. There are two interlaced
fields of about 240 scan lines for a total of about 480
sacn lines that carry picture information. There are 525
total line including sync and such. Each scan line has analog
waves that have no digital resolution until there are sampled
and digitized. The horizontal sample timing is independent of
how many of the scan lines are being sampled so 720x160 and
160x480 are valid (but don't make much sense in practice ;-).

>  Of course,
> as far as capture goes, you do get some benefit by sampling
> at double the horizontal resolution.  However, there isn't
 > much reason to sample at double the vertical resolution.
 > 320x480 for an NTSC signal should not look noticeably
 > different than 640x480.

It is noticeably different because there are 480 unique scan
lines of information and the higher horizontal timing will
preserve more detail. Because of the low quality of broadcast
television, lowering the width will usually do more good by
saving disk space and CPU time than harm by lowering the
perceived picture quality. See:

http://www.mythtv.org/docs/mythtv-HOWTO-19.html#ss19.4

--  bjm