On Sat, 7 May 2005, Dik Takken wrote:
> I just couldn't wait any longer for the release of MJPEG Tools 0.7, so I
> finally decided to take the jump to the latest CVS version. Most of my
As we say here (perhaps you've a similar saying): don't hold your
breath - you turn blue that way :)
> shell scripts were still working perfectly, except for the denoising part.
Yes, yuvdenoise was rewritten a while back and the manpage hasn't been
updated to reflect the new options.
> I use MJPEG Tools to process my digital video camera recordings and
> translate them to MPEG2 streams. Especially in low light conditions
miniDV or Digital8? Is the capture done over a IEEE1394 cable or
via analog conversion from the S-Video/composite output of the
camcorder? If there's an analog step involved then some (more) noise
will sneak in.
> (like inside my home) there is a *lot* of chroma noise in the recordings:
> On a 100% grey background you can see small patches of slightly red
> colored pixels that appear at random and never last longer than 1 frame.
CCD noise :( Small CCDs (consumer camcorders often use 1/6" CCDs,
the more expensive ones 1/4.7" and the pro-sumer models 1/3") are
quite susceptible to that.
> Especially in the shadows, the red colors are jumping up and down like
> crazy. Previously, I used 'yuvdenoise -f' in the processing pipeline, ...
> Although the -f switch of yuvdenoise is still documented as valid in CVS,
> it seems to be deprecated.
More than deprecated - it's been removed :)
> So, I tried using 'yuvdenoise -t 1' but it
> acted like a digital sledgehammer: The picture looks 100% noise free and
> blurry. Even 'yuvdenoise -t 0' is far, far too agressive.
Hmmm, current cvs yuvdenoise does not have a '-t' option that I can
see. The usage summary (or looking at the getopt() call in the
source module) show:
INFO: [yuvdenoise] -Y [n] spatial Y-filter-threshold
INFO: [yuvdenoise] -U [n] spatial U-filter-threshold
INFO: [yuvdenoise] -V [n] spatial V-filter-threshold
INFO: [yuvdenoise] -y [n] temporal Y-filter-threshold
INFO: [yuvdenoise] -u [n] temporal U-filter-threshold
INFO: [yuvdenoise] -v [n] temporal V-filter-threshold
Additional threshold values need to be specified. The defaults
(especially the spatial) are far too aggressive for the luma and
soften/blur the image very much.
The default value for -Y (spatial luma) is 5, I think 1 or 2 would be
better. For -y (temporal luma) the default is 10 and that is much
too high - something like 3 or 4 would be better I think.
> So, I decided to try the new y4mdenoise. This utility did not seem to have
> a subtle bit noise remover either. I tried 'y4mdenoise -t 2 -T 6 -z 1 -Z
> 5' which seems to come close to what 'yuvdenoise -f' could do. These
> settings are quite agressive, but less agressive settings fail to remove
> the chroma noise.
Actually I think those settings are quite mild and not aggressive
at all. "-t 2 -z 1" is usually dones as a "finishing" step since it
is so non-aggressive.
> What is the best way to attack this kind of noise in current CVS, and is
> there any good replacement for 'yuvdenoise -f' ?
You might try 'yuvmedianfilter' on the chroma only. To disable luma
processing use "-t 0" and then experiment with "-T" values to set the
chroma thresholding. There is also a "-f" (fast/averaging) option for
yuvmedianfilter that may be useful.
If the noise is primarily in the darker areas then 'desaturating the
lows' (removing some of the color info from darker areas) might help
but I only know how to do that with FinalCutPro.
Cheers,
Steven Schultz
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