Archived from groups: alt.tv.tech.hdtv (
More info?)
This has been a very interesting thread so far.
Could somebody be kind enough to explain a little bit more about the
"rolloff" and the factors contributing to it?
"John S. Dyson" <toor@iquest.net> wrote in message
news:c7eej4$1kae$1@news.iquest.net...
> In article <MPG.1b0457ac71a6ecc2989702@news.gwtc.net>,
> Steve Rimberg <rsteve@world1.net> writes:
> > In article <c7c2i1$u6i$8@news.iquest.net>, toor@iquest.net says...
> >
> >> No... You see the stationary detail in both phases of the interlace
for
> >> 1080i.
> >
> > And you get "judder" or "jitter."
> >
> Not really -- dynamic filters are cool (effectively, there is already
> dynamic filtering going on in MPEG2 encoding.) When the 'flicker'
> starts being possible, then you increase the amount of interlace
> filtering. Since the detail is aliased anyway, removing the motion
> artifacts is actually almost information neturl.
>
> >
> >> In essence, interlace is a tradeoff that trades-away temporal
resolution
> >> so as to provide better spatial resolution for a given frame scanning
> >> structure.
> >
> > Interlace is an obsolete, 70 year old "technology" used to thin out the
> > information stream to make it fit through a limited bandwidth pipeline.
> >
> Interlace exists, and it works. It might be suboptimal, but much less
> suboptimal than 720p60 on filmed material where 1080i30 certainly can/does
> look better. In the future, a little de-interlacing will help those
> old film/tape archives continue to be valuable.
>
> >
> > Modern compression technology has eliminated the need for interlace.
> >
> So what? If you want the real 'ideal', then the filmed stuff should
> be broadcast at 1080p24. 720p60 is silly on most material, considering
> that it is filmed (or film-look.)
>
>
>
> >> When comparing 1080i vs. 720p, it is also important to NOT forget the
> >> 1280H pixels vs. the 1920H pixels.
> >
> > You keep repeating this falsehood for some reason, and I'll keep
> > repeating the correction. As it exists now, 1080i is 1440 by 1080
> > pixels.
> >
> You keep on forgetting the necessary rolloff (which isn't as necessary
> when the sampling structure is 1920H instead of the very very limited
> 1280H.) Either you don't realize, or are purposefully forgetting that
> the rolloff for 1280H usualy has to start at about effectivelly 800 or
> less TVL to avoid uglifying. Even if all of the 1920H doesn't exist,
> the needed rolloff for avoiding sampling effects would typically start
> being significant at the 1000-1100TVL level.
>
> >
> > 1080i has the edge in horizontal resolution, but not by much.
> >
> > 720p has the edge in color resolution, in vertical resolution, and in
> > temporal resolution.
> >
> If you look at real numbers, you'll find that for 'resolution' figures,
> even in the best case, 720p is a toss-up. Temporal resolution is
essentially
> the ONLY advantage of 720p60. Also, if you really have ever seen 720p,
> the effects of the early rolloff for the 1280H anti-aliasing makes it
> look like a 'fantastic 480p' instead of that 'window' 1080i or 1080p
> effect.
>
> >
> >> Given the above, except for sports (esp for filmed material), 1080i is
> >> the GENERALLY best format. This is most true for film, where
information
> >> can be reconstructed very nicely to give ALMOST 1080p type (not full,
however)
> >> performance.
> >
> > You've obviously never had to reconstruct an image shot interlaced in-
> > camera. De-interlacers don't work well at all.
> >
> Plaeeze!!! 24fps material (be it 1080p24 or film) is easy to reconstruct
> when it is played out on 1080i30 formats. The problem with DVDs is that
> the proper flags aren't always used.
>
> If you start with 60fps material, then 720p will work better for motion.
> If you start with 24fps material (most scripted stuff), 1080i or 1080p
> (depending upon display) is a better match. 720p is silly for 24fps
> material, with no advantages.
>
> If you start with 'video look', then it is best to match the recording
> standards, where 1080i is probably the best all around except for motion,
> and does give the best video look. For sports or scientific work (where
> freeze frame is a primarily used feature), then 720p can be useful.
>
> One more note: for broadcast HDTV, 1080i is a tight fit. High motion
> and 1080i is a disaster sometimes, but not because of 1080i encoding
> itself on the ATSC channel. It is because of the all-too-common
> subchannels that force the 1080i to fit in 15mpbs.... That is very
> marginal for 1080i. This gives a double bonus for sports on 720p60,
> where it tends to fit into the ATSC channel, even with a subchannel
> or two.
>
> John
>