Hi Nicolas,
Nicolas schrieb:
> I don't apply any filter. I spent 2 evenings trying to find good
>
>settings to denoise the video without any success. Each time the result
>was blur. There was far less details on the pictures...
>
>
hmm,...
you could (do you use the CVS version of the denoiser?) use -M 0,0,0 -m
0,0,0 -t 8,16,16...
Blurring only should be visable when using too high thresholds for the
spatial filters (-M and -m). When appropriatly set you shouldn't be able
to see any blurring even with these. The above example, however, turns
the spatial filters off, completely. The temporal filter, however, can
*not* reduce sharpness (it might, if using thresholds above 24 (which is
a really huge setting!) cause visable ghosts.) So, if you want to
denoise without loosing sharpness by all means use only -t...
BTW: if it is any analoge video tape, you should use horizontal
lowpass-filtering, at least *once* in your chain. Here comes why (you
may not like to hear... Warning, long...):
You say it's a recording of a HI8 tape. These have a bandlimit of 3Mhz
(luminance) applied before recording the video signal on tape. Sampling
theory says you'll be needing 6.000.000 samples/sec to get a fully
reconstructable digital recording of such a signal. Samples is pixels
for digital images. Asuming you're recording a PAL signal to such a
tape you have 25 frames (= 2 fields) per second. This makes
6.000.000/25=240.000 pixels per frame. PAL has 625 scanlines per frame,
so you get 240.000/625=384 pixels/scanline. This is further reduced by
the horizontal blank-interval. For PAL it has a time-period of 4,7µs.
The complete scanline has a time-period of approximatly (I ignore vsync
here...) 64µs. So approximatly 7,3% of the complete scanline is lost for
image transmission. This makes 384*(1-0,073)=356 pixels of resolution.
Considering the active lines of a PAL-video (and I don't know a
digital-video-system which stores more than that) to be 576, you will
end up with an image of 356x576 active/usable pixels by maximum. For a
standard (that is luma correctly bandlimited to 5Mhz) PAL-signal you
will end up with an image of 593x576 pixels. Everything you record above
these limits is *noise*... That noise however may mask how bad the HI8
recording really is...
Furthermore the maximum vertical resolution of an interlaced image is
reduced by the Kell-factor to approximatly 2/3*nr_of_lines. This is
reflected in the method any good interlaced TV/video-camera will sample
the image off the CCD. Every halfway sane manufacturer will use
"double-scanline-readout" to
1. reduce noise (+3dB SNR)
2. reduce inter-field-flicker
3. reduce inter-field jumpyness of scanlines
4. honour the Kell-factor as otherwise fine detail may not recorded
at all (if it has the correct, critical velocity)
That is, given this is the CCD:
1. line
2. line
3. line
4. line
5. line
.
.
.
For the first field (bottom field first) scanlines (2+3)/2 and (5+4)/2
and so on are read out, for the second field it's (1+2)/2, (3+4)/2, ...
and so on...
Everyone clearly can see this will reduce resolution before recording
anything. To get that lovely crisp images we all like from (cheap)
video-cameras, boosting of mid to high frequencies is applied, which
makes the image even more worse...
>minutes long Hi8 cassette
>
>I fear that could reduce the video quality.
>
It's HI8... What quality? ;-) (Sorry, could not resist...)
cu
Stefan
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