Hi,
Good question. A DVD offers a video version of a film and in some cases supplements as well. I'm not going to talk about supplements except that I do not consider them an asset unless they do not reduce the image and sound quality of the film itself (and they usually do by taking bits away from the main feature).
For me an excellent/reference DVD is a DVD that
- looks like the film master used (as good as possible given
the limitations of the medium compared to 35mm film) and
not like digital video, especially artifact ridden video.
Naturally the better the film master is the better the
DVD can look as well. Excellent DVDs need an excellent
film master to fully use the potential of the format.
- looks good even on the most revealing watching conditions,
such as when projected on a 2-3m screen with a state of
the art CRT or DLP projector. And not only when watched on
low resolution standard TV monitors sitting 7 or more
screen heights away and with suboptimal lighting
conditions (bright room instead of dark room).
Excellent DVDs are rare among Western DVDs and not
(yet) existent among Indian DVDs.
The reason is it costs more than a run of the mill DVD and
you need to know exactly what you are doing during the
mastering stage. Unfortunately many don't want to spend the
money or don't know/care how to get the film look and avoid
the video look.
To get a superior film-like DVD one must
- transfer from original film elements, using digital
component video (HD -> PAL/NTSC or direct to PAL/NTSC)
- use a state of the art telecine that produces sharp
pictures (almost) free of digital artifacts
- use the correct theatrical aspect ratio and 16:9
enhancement for widescreen films.
- master the NTSC DVD with a corrct 2:3 pulldown so correct
progressive film frames can be reconstructed by
progressive DVD players and external video processors that
have inverse 2:3 pulldown implemented. Do not do format
conversion from PAL to NTSC, NTSC to PAL, HD to PAL/NTSC
which compromises the original film frames and introduces
motion artifacts during playback. If you do the film look
is lost and it looks like video, even if everything else
is done optimally.
- color and contrast correct the film digitally for optimal
playback with 8bit video, preferably in the telecine or
on the 10 bit HD master so rounding errors and
recompression artifacts are minimised.
- use a state of the art MPEG encoder and use a high enough
bit rate to handle the enormous detail present in a sharp
transfer. Optimise the compression by carefully tuning the
MPEG-2 parameters to the image content.
- not optimise for small TV screens where some edge enhance-
ment usually looks 'nice', but looks ugly on bigger
screens. People that like the pseudo sharp look can use
their TV sharpness function. Forcing everbody to endure
enhanced edges makes no sense. It also destroys the film
look. Don't use edge enhancement at all. Make a naturally
sharp transfer and use a high bit rate if sharpness is
what you want (and hopefully you do!).
- not reduce sharpness in horizontal or vertical direction
with a low pass filter so a lower bit rate can be used
and there is less flicker on interlaced monitors.
- not apply noise reduction to the transfer since it
inevitably leaves a trail of artifacts behind that again
destroys the film look. If the film master is too noisy
use a better master. If none is available encode at the
highest bit rate. Use high quality digital restoration
methods if film defects are too annoying otherwise, but
not a real time general purpose noise reducer. Be aware
that edge enhancement and noise reduction is often per
default built into and active in telecines and MPEG
encoders alike and may actually be active while you are
not aware of it. In some brands/models you can't turn it
off, EVEN IF YOU WANT TO! In that case ask for software/
hardware updates and insist on the possibility to turn
it off. This situation is wide spread and affects top
films like "Star Wars: The Phantom Menace" which has some
excessive edge enhancement. But Fox plays dumb and denies
they applied any. A simple look at the picture proves them
wrong. Scary.
- Concerning sound quality use again the best sound masters
available. Use the high bit rate Dolby Digital or DTS.
Don't generate pseudo 5 channel mixes from mono sources
and don't reduce the dynamics of the master. Instead map
the loudest sound of the audio master to 0DB so the full
digital resolution is used and no bits wasted.
If you do all of this you will get a DVD that looks and
sounds remarkably like the film master, film-like, natural,
including the masters artifacts (speckles, scratches, grain,
out of focus shots etc.). If you want to get rid of the
film masters artifacts use a better master or CAREFULLY
apply digital methods that do not add any new (visible)
artifacts.
Such a DVD looks better than bad HD-TV. Actually most non
experts will think it is HD-TV when watching it with high-
end equipment. It looks great! Only good HD will clearly
show the still existing limitations of such a DVD (except
for good 35mm prints, of course).
cheers
Michel Hafner
http://www.imdb.com