Quantcast Removing flicker from VHS tapes? - digitalFAQ Forum
  #1  
02-25-2020, 07:47 AM
hysteriah hysteriah is offline
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Hi all you good people. I'm hoping for some good suggestions :-)

I have a few clips, recorded from some old PAL VHS tapes that was recorded from regular cable TV broadcast signals back in 1993/1994. They've been digitized using a rather Hi-Q JVC SVHS deck suggested on this site. Unfortunately the VCR's built in LTBC caused problems (to much vertical jitter) so it had to be disabled during digitizing. Therefor the signal was feed thru a Panasonic DMR-ES10 DVD recorder used as a pass-thru, to a LSI chip based DVD recorder for recording. I'm totally aware of that these technique and rather low quality MPEG-2 files is not optimal for restoration work, but they'll have to do for now. I still hope that there's something I can do to improve the quality just a littlebit. I'm not expecting any miracles, though

In fact, I'm quite happy with the overall quality of most of my clips, but some of them do suffer from this very anoying "flickering effect". It seems like the odd and even fields was broadcasted/recorded with a littlebit of difference in "brightness/contrast-level". It becomes specially anoying in bright scenes, creating this kind of a blinking strobe-alike effect (check the attached "test.mpg" file) for a sample. I would really like to reduce this effect if at all possible? Btw, I'm pretty sure that this issue was caused by the broadcast signal from my cable tv provider back in the day, not by the digitizing process.

I'm totally new to restoring, filtering and improving video quality, and I'm even newer to AVISynth scripts, so please keep that in mind when responding. I'm now planning to deinterlace, upscale and encode a few clips to H264 format, just for sharing with a couple of friends online... and I wonder if there's any nice and easy to use AVISynth filters/plugins that could be added to the chain of filters to reduce this very anoying flickering effect as well?

Any suggestions will be highly appreciated

The AVISynth script that I'm planning to use for deinterlace and upscaling is:
Code:
SetFilterMTMode("QTGMC", 2)
FFmpegSource2("test.mpg")
ConvertToYV12()
AssumeTFF()
QTGMC(Preset="Slower", Edithreads=2)
Crop(8,0,-8,0)
Spline64Resize (960,720)
Prefetch(threads=6)


Attached Files
File Type: mpg test.mpg (39.33 MB, 11 downloads)
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  #2  
02-25-2020, 10:16 PM
msgohan msgohan is online now
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Excellent choice of sample content: black & white fields in same frame with mid-range color, skintone with white shirt, etc.

I can tell you that manual correction is impossible. We seem to be battling AGC, probably multiple AGCs given the signal path you described. A correction that works with one scene is wrong when it cuts to the next scene.

Besides, the levels vary significantly just comparing top & bottom of each field.

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The bright part of the histogram would ideally be a straight line, but instead it has a big curve at the top, and a slight slope overall.

One potential method, slow but automatic, would be to export all Even fields and all Odd fields as images to folders, and run DrDre's color matching tool to bring the "bad" one in line with the "good" one. It's been years since I've played with that, though.

This is the manual correction that I tried:
Code:
MPEG2Source("test.d2v")

SeparateFields()
Eve = SelectEven().Levels(0,1,240,4,255,false,true)
Odd = SelectOdd().Levels(0,1,250,0,255,false,true)

Interleave(Eve,Odd)
Weave()


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  #3  
02-26-2020, 05:15 AM
hysteriah hysteriah is offline
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Wow! Thank you very much, msgohan, for your extensive answer. I'm forever grateful

The method you describe as exporting all Even fields and all Odd fields as images to folders, and run DrDre's color matching tool on them, sounds very interesting. I don't mind if the process is slow, as long as it's automatic. I think I have a computer that I could dedicate for this kind of task. If it takes days, weeks or even months doesn't really matter, as long as it's automatic and the results are getting good

Could you please guide me in the right direction on how to export all Even fields and all Odd fields as images to folders and afterwords get them back together, by using AVISynth scripts?
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