interlaced video

Posted Jan 24, 2008 11:24 UTC (Thu) by tialaramex (subscriber, #21167)
In reply to: The Grumpy Editor's video journey part 2: Video editors by jwoithe
Parent article: The Grumpy Editor's video journey part 2: Video editors

In principle, the parent comment is correct about interlacing, but it's not apparent to me
that it's necessarily desirable now in 2008

A "normal" interlaced TV was the only thing in people's homes in the 1990s when DVD was
introduced. However most of the material people are actually watching on DVD, that is, movies
and high budget TV productions was shot on film (or a film-like digital process), and so no
true interlaced source exists. As a result what's actually on the DVD is essentially 24 fps
progressive scan, and the interlacing is created during playback.

[ It's possible to use the same telecine process an analog TV channel uses to broadcast a
movie, and then record the interlaced result on DVD, and in a few famous cases this has
actually been done to movies you've heard of, e.g. some releases of The Princess Bride, but
it's acknowledged that this is the Wrong Thing ]

In another decade, with CRTs gone from most people's homes, interlaced video may be solely a
legacy format. At that point approaches your choice for old home videos, where the source
material really is interlaced will be between relying on a realtime de-interlacing filter in
your DVD playback hardware or television, and doing it once with high quality software as our
Grumpy Editor elected to.

interlaced video

Posted Jan 24, 2008 23:41 UTC (Thu) by jwoithe (subscriber, #10521) [Link]

I agree that the move away from "traditional" TV devices, video interfaces and delivery
methods in favour of non-interlaced and computer-based options is slowly making interlaced
video a legacy format. I also suspect that the speed at which interlaced formats become
deprecated will be different in almost every country.

Having said that, a vast majority of people I provide video to are still running AV equipment
which relies on standard PAL interconnects - and that means interlaced video. For such
people, providing a deinterlaced 25 fps program (25p) will result in an obvious drop in
quality compared to 25i (and is in fact a lossy operation if starting with 25i source
material). Obviously everyone's situation is different, but in this case 25i is a format
which provides the best result for everyone: those with 25i equipment get the best result they
can hope for, and those with gear capable of 50p will still get an acceptable picture due to
deinterlacers in their players/tvs (which aren't all that bad even now). Note that
distributing with 50p isn't really an option yet since few people have players capable of
dealing with this format (DVD doesn't).

While the above refers (obviously) to PAL land, similar statements apply to NTSC.

It should also be noted that in our editor's case (as in mine), the source material was almost
certainly interlaced, so his deinterlacing operation from 30i to 30p was in fact lossy.

This whole area is a minefield and looks set to remain that way for some time to come.
Ideally interlacing would just go away, but there's a huge installed base of interlaced
equipment which guarantees that this will be a long drawn out process. Until that process
completes one has to be aware of all the issues and make a call based on their particular
circumstances.

interlaced video

Posted Jan 25, 2008 7:21 UTC (Fri) by njs (guest, #40338) [Link]

Almost all current HD broadcasts are interlaced too ("1080i"), and will be for some time :-(.
AFAIU the reason they do this is that for most shows it's actually considered superior to the
equivalent progressive format ("720p"), because at a given bit-rate, interlaced video gives
better spatial resolution at the cost of some temporal resolution.  Maybe.  Something like
that.

Looking forward to ubiquitous 1080p, myself.  (At last, something to use those terabyte drives
for!)