Re: PAL Video Capture

Michel Carleer (mcarleer@ulb.ac.be)
Wed, 16 Apr 1997 14:42:18 +0200


Adrian Close wrote:
>
> Use of PAL/NTSC should not make any difference to CU. The capture card
> handles the incoming video signal and makes it available to CU in digital
> format via the Video for Windows drivers (for PC - I don't know how Macs
> handle this, but it shouldn't make a difference).
>

Adrian,
IN PRINCIPLE you are right, PAL or NTSC makes no difference as long as you
have a video card with the appropriate tuner (in fact most of them, at
least here in Europe, decode both formats).
I said in principle, because there is a catch: International standards (I
don't remember the name of the issuing organisation, it has something to do
with MPEG compression) recommend to digitize PAL with a spatial resolution
of 352 x 288, and NTSC with a resolution of 320 x 240 (or multiples and
sub-multiples of these base resolutions). The two different formats come
from the fact that PAL pictures consist of 625 lines, whereas NTSC only
uses 515. Because of these standards, some PAL digitizing cards simply
refuse to use anything else than 352 x 288 or 176 x 144, etc... But as you
know, CU-SeeMe only knows about 160 x 120 and 320 x 240. And that's why
some PAL cards are incompatible with CU-SeeMe.
So, if you have to buy a PAL video card, check that they accept to digitize
in 160 x 120 and 320 x 240. And of course remember that CU-SeeMe only knows
8-bit colour or 4/8-bit grey colour encoding formats (+ some others like
YUV or Indeo, which are compressed formats), so don't forget to check this
out too.
Hope this clarifies a bit,

Mike

Michel R.C.E. Carleer
Chimie Physique Moleculaire CPi 160/09
Universite Libre de Bruxelles
Ave. F.D. Roosevelt, 50
1050 Bruxelles
Belgique
Tel: +32-2-6502425
Fax: +32-2-6504232
e-mail: mcarleer@ulb.ac.be