Quantcast Discolored frames in VHS capture? - digitalFAQ Forum
  #1  
10-18-2020, 04:59 PM
maldata maldata is offline
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Hi all,

I have a few VHS tapes that I'm capturing digitally. I've been poking around the forums here, and there definitely are many things I could be doing better, but I'm generally pretty happy with the results I've been getting with the hardware I've got.

I've done a few tapes already that came out looking good, but the one I'm working on now has some weird color variations that I have not seen on other tapes. In short, it looks like the colors flicker a little bit, suddenly becoming pinker or yellower and then back again. I attached an image here showing two screenshots taken from two consecutive frames in the capture. As you can see, the color in the top half (first frame) looks very different from the bottom half (second frame). This is not a problem I've seen on other tapes I've captured with the same VCR & capture card.

My guess, then, is that this is just something that happens on old tapes that have been watched a thousand times. Does that sound accurate? Or is there something else that might be going on? If that is the case (this is just for curiosity's sake), what happens to the tape with time & use to cause this? Is there any particular kind of filter that can be applied to improve how it looks?

Though I don't think the hardware or software is the issue, for completeness, I'm using:
  • Samsung DVD-V2000 VCR
  • Composite output
  • PCHDTV 5500 capture card
  • gstreamer for capture
  • ffmpeg for filtering & compression
Let me know your thoughts. Thanks!


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File Type: png vhs-frame-compare.png (175.4 KB, 21 downloads)
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  #2  
10-19-2020, 05:37 AM
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That exact Samsung isn't a bad deck, like most, for being a mere consumer VHS VCR. The main issue is the OSD for tracking can't be shut off.

However, you lack any sort of TBC functionality, and that can't look good. You will have wiggles in the image, and likely other issues. Color can also be affected. And then dropped frames are extremely likely, almost a given. At the bare minimum, you need an ES10/15 for half a TBC(ish). There will still be issues, and a fail rate, but substantially better than what you're doing now.

The Conexant chipset is that capture isn't great, and may have AGC issues. (Is it related to the VC500 chipset? Also AGC, other issues, not great.)

I doubt gstreamer has a dropped frames counter. Does it?

Lack of any TBC/TBC(ish) is a likely culprit here. But the whole workflow has weaknesses. At under $200, the ES10/15 (cheap) should be a no-brainer. And if you want a full TBC(ish), DVK+ES10/15, I have a modded/preset DVK in the marketplace.

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  #3  
10-19-2020, 01:54 PM
maldata maldata is offline
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Quote:
That exact Samsung isn't a bad deck, like most, for being a mere consumer VHS VCR. The main issue is the OSD for tracking can't be shut off.
I'll second that for sure. Some of my tapes are recordings that start very close to the beginning of the tape and there's no way to capture it without the display getting captured as well.

Quote:
However, you lack any sort of TBC functionality, and that can't look good.
True, and that's why I wanted to post here. I'd like to get a better understanding of the signals involved and how they can be cleaned up. I'm a little reluctant to throw hardware at the problem because these tapes aren't an historical archive... they're just dumb TV shows from my youth. I get decent results from the hardware I've got, by which I mean, everything is "watchable." It could certainly be better, but it's hard to justify the expense when I don't really know what TBC is all about or what kinds of problems it can fix. This one is the most noticeable issue I have, so I wanted to get input on it in particular.

Quote:
The Conexant chipset is that capture isn't great, and may have AGC issues. (Is it related to the VC500 chipset? Also AGC, other issues, not great.)
I'm using this capture card because I already had it for OTA HDTV, and it runs well on a linux system. I actually didn't even know the card had an analog input until a few weeks ago, which is what set this whole project in motion...

Quote:
I doubt gstreamer has a dropped frames counter. Does it?
There is a sink that shows dropped frames, but I'm not 100% certain yet about frames getting dropped earlier in the pipeline. The API presents some QoS features, but I haven't gotten deep into it yet. I have been very happy with its performance, though!

Quote:
Lack of any TBC/TBC(ish) is a likely culprit here. But the whole workflow has weaknesses.
I don't know much (virtually nothing) about TBC/TBC-ish devices, so this is the kind of insight I was hoping for. I'm curious to know more about what a TBC (or TBC-ish) device does that would correct color distortion, and why that would only happen on certain tapes to begin with. I'll dig a little deeper, but by all means, if you've got resources that describe it clearly to newbies, let me know.

Quote:
At under $200, the ES10/15 (cheap) should be a no-brainer. And if you want a full TBC(ish), DVK+ES10/15, I have a modded/preset DVK in the marketplace.
If I could convince myself that saving these weird old shows was worth it, I'd be happy to invest in a new deck, a new capture card, etc., but I'm also interested in what (if anything) can be done with what I have on-hand. The answer may very well be "nothing," but I want to make sure I learn as much as I can first before making that decision.

Thanks for the help, I appreciate it!
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  #4  
10-19-2020, 04:10 PM
hodgey hodgey is offline
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Quote:
Originally Posted by lordsmurf View Post
(Is it related to the VC500 chipset? Also AGC, other issues, not great.)
I think it differs a bit, it's based on the older BT878 chipset conexant aquired from brooktree (the similarly named pci-express chips are closely related to the one used in USB dongles though judging by the datasheet for those). I have two cards with the chipset myself, though I've barely used them (got them mainly for raw data capture with cxadc). They have some sort of feature (termed UltraLock) that seems to help avoid loosing sync, so it seemed to work a little better than the VC500 and similar on a raw signal. The image is still very wiggly and Y/C filtering is very bad on any video that's not stable.
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  #5  
10-19-2020, 08:11 PM
Hushpower Hushpower is offline
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Maldata, have a look at this thread:

How to fix green-purple flashes when digitising?

It'll show you what the ES-10/15 can do.

Cheers, Al
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  #6  
10-20-2020, 08:43 AM
hodgey hodgey is offline
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On the PAL Samsung models you can turn off the OSD in the menu, and adjust the sharpness. I wonder why that's left out on the NTSC ones.
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  #7  
10-20-2020, 11:43 AM
maldata maldata is offline
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From the thread Hushpower sent:

Quote:
It should, the reason the color is messed up is that the capture card loses track of where the line starts. The start of the each line (which you don't see normally as it will be cropped off) contains the reference color signal (color burst) whatever is trying to decode the color needs to get the hue of the color data in the line correct. The Video decoder in the ES15 and your TV is much better at this.
Interesting! That makes sense. So, if I understand correctly, a little bit of variation in the timing of the sync pulses could be misunderstood by the capture card, and then you end up with some frames that have messed up coloration. Is that right?

What I was trying to get from this discussion is some confidence that either the problem was the tape (e.g., "that's just what happens as tapes age") or something fixable (e.g., "you need to clean your VCR").

It sounds like the consensus is that you just really need something to fix that signal sometimes. That's fair, I just have to find a good balance between what I'm willing to spend on this project and what's available to do that work.

Maybe this should be in a separate thread, but has anyone looked at the guts of the ES15 to see what video decoder chip is in there, and if it's in any other products? I went down a pretty deep google rabbit-hole last night and saw some discussions (on this forum and elsewhere) about things like video scalers that have some line TBC features. I wonder if the ES15 uses the same chip as other cheaper, more widely available devices.
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  #8  
10-22-2020, 05:00 AM
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Quote:
Originally Posted by hodgey View Post
On the PAL Samsung models you can turn off the OSD in the menu, and adjust the sharpness. I wonder why that's left out on the NTSC ones.
OSD on/off is in the 5000W menu.
But I didn't see it in the V1000 menu (either that, or tracking OSD was on regardless of setting, I forget).

Quote:
Originally Posted by maldata View Post
Interesting! That makes sense. So, if I understand correctly, a little bit of variation in the timing of the sync pulses could be misunderstood by the capture card, and then you end up with some frames that have messed up coloration. Is that right?
Bad timing can affect chroma, yes.

Quote:
It sounds like the consensus is that you just really need something to fix that signal sometimes. That's fair, I just have to find a good balance between what I'm willing to spend on this project and what's available to do that work.
TBC(ish) is the budget path, ideally DVK+ES10/15

Quote:
Maybe this should be in a separate thread, but has anyone looked at the guts of the ES15 to see what video decoder chip is in there,
Long ago, yes. ES10, back in 2005. Same as ES15. Most are Panasonic in-house chips. (That was actually known already, Panasonic advertised this, but opening it up was just confirmation.)

Quote:
and if it's in any other products?
No.

Quote:
I went down a pretty deep google rabbit-hole last night
Video has lots of rabbit holes. I've been falling down some holes for a decade now, always something new to learn or glean.

Quote:
things like video scalers that have some line TBC features.
No. Scalers do not. Not in terms of the TBCs needed for consumer analog sources.

Quote:
I wonder if the ES15 uses the same chip as other cheaper, more widely available devices.
No. Proprietary.

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  #9  
10-29-2020, 11:54 AM
maldata maldata is offline
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Well... you talked me into it. I broke down and got an ES15, and I haven't seen the problem since. Also, everything is less wobbly.

Ended up learning a lot here, and you fixed my problem, so A+, would post again (in fact, about to)!

Thanks, all! Definitely appreciate the help.
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  #10  
10-29-2020, 05:35 PM
Hushpower Hushpower is offline
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Great stuff maldata, the "TBCish" ES15 strikes again!
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