Simple Mpeg2 encoding question for all you smart guys

I know that encoding VHS to Half D1 for DVD is fine because the resolution
of VHS is below or equal to that of Half D1. What about 8mm and Hi8? What
are the resolutions of those two formats and will Half D1 harm them?

Thanks

Sanman

 

I don't claim to be a smart guy but I can tell you that (aproximately) 8mm =
VHS and Hi8 = SVHS. Therefore, I wouldn't expect half D1 to hurt 8mm but I
would expect to see a quality hit from Hi8.

Mike

 

8mm is about 260 lines horizontal resolution, Hi8 around 400 lines.
Each would look fine in Half D1 resolution, which is 352 horizontal.

As discussed earlier, if you are using a low bitrate, it will look
better in half D1 compared to full D1.


-WD

 

No. You're confusing "lines of horizontal resolution" with "pixels
across the horizontal". For reference, DV has 540 lines of horizontal
resolution (in 4:3 aspect ratio), but 720 pixels.

The whole "lines of resolution" measurement goes way back into
pre-digital optics, on film. It became a significant measurement for
video, across the horizontal, since that was essentially a measurement
of the system's bandwith, with the lens, imager (back in the vidicon
tube days) and the horizontal all being analog in nature.

In digital terms, the line resolution across the horizontal is the
number of pixels (more or less) that run across the horizontal of the
largest perfect circle you can inscribe in your visual field. In DV or
DVD, in 4:3 aspect ratio, that's 720 * 3/4 = 540 (in 16:9 aspect
ratio, that's 720 * 9/16 = 405).

So flippimg back, if you're dealing with an analog format like Video8
that's delivering 260 lines of horizontal resolution, you should be
able to get a reasonable digital representation of that in ~350 pixels
across the horizontal. So the 352 you get in Half-D1 does the job. For
Hi8 or SVHS, something in the 400 line range, that's going to need
about 540 pixels across to be well represented. You're going to want
to run a full D1 capture to do justice to either of these.

Keep in mind that digital sampling of an analog signal is ALWAYS an
approximation, at best. The nature of analog is that a color can
change anywhere along the horizontal. Professional titlers and other
graphics, for analog broadcast, usually work in 1500-2000 pixel
resolutions to deliver the kind of smooth graphics you see on the
networks. The analog limit is bandwith, which doesn't say "you can
only have changes here and there" (that's digital), but rather, "after
you change something, you have to wait N-microseconds for the next
change".
Dave Haynie | Chief Toady, Frog Pond Media Consulting
| Take Back Freedom! Bush no more in 2004!
"Deathbed Vigil" now on DVD! See http://www.frogpondmedia.com