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<< I am referring to the dirt removal application of DVNR. I am very aware of
the good it can achieve, it is the misuse which concerns me. Overuse eats away
at any subtle light reflections, creating a distracting 'pulsating' effect. >>

Those of us who have spent the last decade or so repairing Rank Digiscan 3's
and 4's can probably think of at least 25 ways these effects could be caused
before the video ever gets to a noise reducer.  Not to mention that it's a
pretty good description of what video looks like after it's been through many
of the computerized, offline nonlinear editors out there.  As I mentioned
previously, the video compression used in most of the new tape formats and
elsewhere can also cause subtle or not so subtle artifacts on occasion.
Specifically, the results can be highly unpredictable when compressed video
from one source is played back uncompressed and then recorded by another
device which compresses it again. 

While it is possible that any noise reduction system--whether it be from
Accom, Digital Vision, Philips, or anybody else--could create video artifacts
if misused, their function is to remove electronic noise and film grain, which
are usually smaller in size than the average dirt particle.  They also
normally provide a degree of image enhancement and aperture correction, which
help make the picture look like it's in focus.  The usual results of too much
noise reduction are motion blur, "comet tails," and posterization.  Too much
image enhancement causes "ringing" (rainbows), and moire.  Except for music
videos and material where a special effects look is the goal, these sorts of
things won't be seen coming from a color correction suite in the hands of a
competent colorist.

There are such things as "digital wet gates" or digital dirt removers on the
market, and I've tested out a few different ones.  The usual problem is that
compared to a real liquid gate, the digital ones don't do enough, rather than
taking out all of the dirt and parts of the picture as well.  But if somebody
misused one of these devices by pushing it beyond its capabilities, it could
cause problems such as you note.  Most colorists I know would be very tempted,
in such circumstances, to turn the digital wet gate down, allowing occasional
dirt particles to get through, in the interests of keeping the rest of the
picture as pure as possible.  However, as my colleague Marc Wielage points
out, some producer or studio exec might have felt the image looked better the
other way, and since they're the ones with the open checkbooks, they've got
the last word!

Best regards,
Christopher Bacon

P.S. I am not in the employ of Digital Vision or any other noise reducer

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