On Mon, 5 Dec 2005, Michael Hanke wrote:
> I have some material which is widescreen in letter box format. Since the
> quality is rather high (Digital Satellite --> SVHS-cable --> (re)digitize) I
> am thinking of transforming the picture to DVD_WIDE (720x576 and 16:9). My
> question: is this a good idea or should I rely on the TV-set to do a better
I do NOT think it's a good idea. Upscaling ~20-30% (depending if you're
in a NTSC or PAL area) degrades the quality so much I couldn't watch
it (yes - I've done it and didn't like the results ;)).
> job? If so, which additional filters do you suggest (yuvcorrect CONFORM etc)
> in order to get rid of scaling artifacts?
There's no filter that I know of which can overcome the effects of
upscaling.
The data is already 'broadcast legal' (well, it _should_ be if the
TV station is operating correctly ;)) so "yuvcorrect CONFORM" (which
simply clips/cores the data to broadcast range) will not do anything
to improve the picture. On the other hand it won't harm anything
either :)
If you really want to do it then here's how to go about it.
As an example (and because I know the numbers ;)) for NTSC a 16:9 movie
that has been letter boxed to 4:3 has an active area of 360 lines -
the black bars are 60 lines at top and bottom (60 + 360 + 60 = 480).
Broadcast (NTSC) MPEG streams I've seen are always 704x480 (NOT
720x480!) so that's why 704 is used below. You might need to check
the attributes of the stream (ProjectX is useful for this purpose
as well as demultiplexing the transport streams).
This is all from memory as I go along rather than cut&paste
so hopefully there aren't any typos ;) The assumption is that the
data is top field first - that seems to be the usual field dominance
for TV.
mpeg2dec -o pgmpipe input.m2v |
pgmtoy4m -a 10:11 -r 30000:1001 -i t -x 420mpeg2 |
y4mscaler -I active=704x360+0+60 -O sar=40:33 -O size=704x480 |
mpeg2enc -f 8 -o output.m2v -E -10 -D 10 -4 1 -2 1 -q 4 ...
Now for PAL, with it's different sample aspect ratio the numbers
are slightly different. I'll spare you the boring arithmetic details
but I think this is what would stand a good chance of working:
mpeg2dec -o pgmpipe input.m2v |
pgmtoy4m -a 59:54 -r 25:1 -i t -x 420mpeg2 |
y4mscaler -I active=704x432+0+72 -O sar=118:81 -O size=704x576 |
mpeg2enc -f 8 -o output.m2v -E -10 -D 10 -4 1 -2 1 -q 4 ...
Personally I'd leave the data along and watch it letterboxed. The
decision to toss away the extra lines has already been made and
upscaling and re-encoding will degrade the image. Depending on how
critical your viewing needs are the quality might be acceptable but
I did not care for the results.
Cheers,
Steven Schultz
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