On Mon, 21 Mar 2005, Richard Ellis wrote:
> What you are likely seeing there is the limits of the accuracy of the
> ADC of whatever encoded the video. I.e., ADC noise, which will
Not really - unless Canopus' quality took a huge drop. Note the
rather huge percentages - it's not just a little ripple, but is
several percent.
> What about having a "selective median" (for want of a better term)
> type filter. What I'm thinking is a median type filter that becomes
> more aggressive as the overall luminance of the frame / block becomes
> darker.
I started on that, had a prototype program that displayed the areas
that would be filtered, and the interest was shall we say a bit
underwhelming so I abandoned it.
My feeling is that desaturating the dark areas (probably by moving
U and V closer to their midpoint of 128) is preferable to propagating
the noise. Medianfiltering would simply create more off-black (color)
blocks rather than blacker areas.
A 60% desaturation and a 10 or 12 unit softening threshold (to avoid
abrubt changes) seems to work quite well.
> Is there any way to perform something like that with any of
> the existing filters? And would doing something like that provide a
Not at the present time. It might not be too hard to stuff something
like that into yuvmedianfilter. Probably better to have a separate
program.
> Well, if the source "tape" is VHS, then the system has taken an
Nope - from laserdisc in this case. If the movie wasn't 'remastered'
or 'restored' and was made from a faded/discolored film then some
correction/enhancement really helps.
Othertimes it's been from a miniDV camcorder and the whitebalance is
off (either from not having set the WB or the lighting conditions
were changing).
> already decimated NTSC color signal and further decimated (ruined?)
> it before recording it onto the tape.
It's not just decimation/reduced resolution - I'm thinking to
the discoloration that happens as tapes/films age.
Basically it's more than just "denoising" but a bit of "restoration"
I've one still showing the "with" and "without" correction that
perhaps I'll post (and wait for the moderator to let it thru the
queue) that the difference very nicely.
Cheers,
Steven Schultz
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