Quantcast VHS luma artifact, dark smears by bright areas, fixable? - digitalFAQ Forum
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  #1  
02-21-2021, 09:40 AM
MetalSlug3 MetalSlug3 is offline
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I'm sure many of you who have worked on VHS have seen the artifact in the attached screenshot.



Basically, when areas of high brightness occur (close to pure white), there is a dark streak to the immediate right that's not supposed to be there.

How is this artifact called, and can I fix this with a vdub/avisynth filter?

I'm working on a losslessly encoded AVI that I captured myself, so I hope I have enough room to maneuver!


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File Type: png vhsSmear.png (701.4 KB, 46 downloads)
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  #2  
02-21-2021, 04:47 PM
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I've not seen anything work on that. I've seen some Avisynth that changed it, but never removed it, arguably even made it look worse (more distracting).

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02-21-2021, 05:55 PM
themaster1 themaster1 is offline
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I think the multi captures technique could work if these "black streaks" are a playback error. The idea is you capture the video 3 or 5 times and you apply a median filter i believe.
There a dedicated thread on videohelp i recall
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02-22-2021, 08:51 AM
dpalomaki dpalomaki is offline
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That may be an artifact of AGC somewhere in the system - the white is seen as perhaps too bright and the gain is reduced to limit the white it to legal levels. When the scan reaches black the AGC releases the gain back to normal levels but that takes a bit of time so the black is too black for a bit. It could also be an artifact of image sharpening circuits. They often work by increasing contrast at image brightness change "edges." It could happen anywhere in the signal chain starting at the camera.

Do you see this in the original tape or only in the captures?
Does your VCR have any image processing or sharpening settings and are they activated?
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02-23-2021, 03:13 PM
MetalSlug3 MetalSlug3 is offline
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Thanks dpalomaki! I had no clue about AGC.
I'm using the Panasonic NV-HS1000. As far as I know, the only user-changeable picture settings are the sharpness slider (which I kept at the midway neutral position during capture) and a vaguely named "AI" function.

I'll have to run some tests playing the tape on a TV and maybe re-capturing it while changing the settings above.

Yet I haven't seen this artifact in other tapes I've captured with this deck.
I actually own two copies of this tape and the artifcat is in both of them. So I think it's more likely that the defect is burned into the tape itself.
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02-23-2021, 04:09 PM
dpalomaki dpalomaki is offline
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The image you posted is from an animation. Do you see the artifact in other animated material with clear, sharp boundaries on objects?

Is there an "Detail" adjustment on your VCR and if so, does that setting, and does it make a difference?

If the AGC effect was in the original recording the playback VCR may have imited ability to do anything about it.
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02-23-2021, 05:55 PM
MetalSlug3 MetalSlug3 is offline
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I've captured a couple of other cartoon tapes that are the same age at the one in my first post, but I haven't seen the artifact there (example attached).

I guess I'll just have to see if tweaking my VCR's settings does anything to my smeary tape!


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File Type: png Pluto.notsmeared.png (721.2 KB, 2 downloads)
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  #8  
02-23-2021, 10:04 PM
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If you ever find a solution, let us know.

I still look, from time to time. This isn't a new issue by any means. Some things just have no fixes, yet, maybe never. I'm not aware of anything that made much headway here, but admittedly also not looked too in depth. Thankfully, don't come across this too often.

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