On Sat, 13 Nov 2004, sean wrote:
> I have some old - late 1980's - vhs tapes that I recorded on my dv camcorder
> from the vcr, and then transferred to my computer.
Ah yes, that's a situation I'm extremely familiar with. I processed
all of my old tapes some time ago (alas a lot of them to SVCD since
DVD authoring didn't exist at the time). A surprising number of the
tapes had not aged well at all - bad color cast, tracking problems,
noise, etc.
> When played as raw files they have lots of blocky artifacts (which are NOT
> present when the orginal tapes are played on tv (ntsc)).
Hmmm, that would seem to point at a less than perfect analog->digital
(DV) conversion.
> They are also quite noisy.
Yep - that's VHS alright...
> I'd like to "clean" these up before I burn them to dvd. I have read the
> howto, but I'd like any suggestions others have. Does anyone have any
> experience cleaning up old tapes like this. What settings, what filters,
> did you use?
The first thing in the "chain" was a color-corrector/image-stabilizer.
Something like the SCC-2 from http://www.simacorp.com/ (at the time
I used the older/first SCC-1 or SCC-Pro model).
After that it was into a Canopus ADVC-100 (today that would be a
ADVC-300 which has hardware denoising capability as well as a TBC
(TimeBaseCorrector - stabilizer).
Then it's off to softwareland. There is a choice of two denoising
programs. "yuvdenoise" and "y4mdenoise". For noisier sources
either "yuvdenoise -l 3" or "y4mdenoise -t 5" (or even -t 6) work
quite well.
The other thing which helps clean up the image a little is to add
in 'yuvmedianfilter -T 3' (or -T 4). This processes only the chroma
(the goal isn't to change the bitrate - chroma doesn't contribute
all that much to the bitrate) and improves the colored areas somewhat.
Oh, probably be a good idea to spatially bandwidth limit ("low pass
filter") the data too with 'y4mspatialfilter'. Won't bore you with
all the details but something like "y4mspatialfilter -L 4,0.75,4,0.75"
is quite appropriate (and conservative) for VHS sources.
The final pipeline looks something like this:
smil2yuv -i 2 input.dv | \
y4mspatialfilter -L 4,0.75,4,0.75 -C 3,0.6,3,0.6 | \
yuvdenoise -l 3 | \
yuvmedianfilter -t 0 -T 3 | \
y4mscaler -v0 -O chromass=420_MPEG2 -S option=sinc:4 | \
mpeg2enc -f 8 -K kvcd ...
The "-i 2" with smil2yuv produces 4:1:1 output (the rest of the
filter chain can deal with that) which is converted to 4:2:0 using
y4mscaler's better chroma conversion capabilities.
For VHS stuff the Kvcd matrices work well and help reduced the splotchy
dark scenes.
Umm, probably should mention that a pipeline like that runs much better
on a dual cpu system than a single :)
Cheers,
Steven Schultz
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