[linux-dvb] 768x576, 720x576, 704x576?! (was: black borders in xawtv)

[Johann Hanne <jonny@xiroi.de>]

On Tue, 26 Feb 2002 jonathan.foster@philips.com wrote:

> PAL is broadcast as 720x576 digital video.  But the analog signal is
> only 702 pixels wide, so 9 pixels each side are left black.

> Yep, crop the image before you display it.

Thanks for the answer. Now I have some more questions. ;-)

Analog PAL is 702x576 (really? not 704x576?). The usual TV has an aspect 
ratio of 4:3, so the picture is somehow scaled to 768x576. So far, so 
good.

"Digital PAL" is broadcast as 720x576 (why 720 and not 702?). However, as 
the source is the analog PAL 702x576 picture, the 9 pixel borders on each 
side are encoded into the MPEG2 stream. Again, the usual TV has an aspect 
ratio of 4:3. When scaling from 720 to 768 i see two problems:
- The black borders are still there as they get scaled as part of
  the picture
- The picture is NOT the same as the analog one: The analog one gets
  scaled horizontally by the factor 768/702, the digital one gets scaled
  horitontally by the factor 768/720. So the analog picture is slightly
  more "stretched" horizontally?!

What I want is simply to get a good picture output to my TV (without 
using the DVB board video out, but by using the TV out of my graphics 
board). Just cropping the picture is not possible, as the TV is fixed to 
4:3 and i want to use the whole screen!
So, as far as i see, there are two possible solutions:
- Take the 768x576 picture with the black borders and scale it
  horizontally AND vertically. The black borders at the left and right
  side will dissapear, but parts of the picture at the top and the
  bottom edge will also not be visible.
- Take the 768x576 picture with the black borders and scale it
  horizontally ONLY. The black borders at the left and right side will
  dissapear, but the picture will be stretched horizontally some more.

What's the way that is used on the video out of the DVB card? I can't see 
any black boarders this way?!

Thanks in advance, Jonny <jonny@1409.org>




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