Why does VHS looks so bad on my computer?

[ricnews]

Hi,

I'm trying to transfer a VHS movie to DVD. I had an ATI TV Wonder PCI and was using Intervideo's WindDVR 2. Whenever I played a tape there would be a horizontal band at the bottom of the screen with either noise or distorted image. I tried the latest ATI MMC software and found it has a "clip borders" option which clips most of it away, but not enough as a thin band of noise at the very bottom remained, with the neighboring image distorted a bit. I also then noticed that at the left side of the screen are several vertical bands where colour is altered so that there are various bands of different colours overlaying the image. These are most intense at the far left and eventually fades into the properly coloured video at around 10% of the video's width from the left edge.

I tried cleaning my VCR which didn't help. I wasn't happy with the capture quality in any case so I put a newer Compro VideoMate TV Gold+ card in. The results with the new card in WinDVR were the same, while the results in the ComproPVR software that comes with the card were similar to the ATI capture software with the "clip borders" option enabled (most of the distortion at the bottom of the video was clipped off but some of it remained). The discoloration at the left of the video also remained.

I tried a number of obvious things to figure out if the problem was with the video capture or if my vcr was busted. to rule out some kind of macrovision problem I played a tape of a recorded TV show and it exhibited the same problems, as did another commercial video VHS. I hooked up a different VCR to my computer and it showed the same effects. I hooked up both the other VCR and the one attached to my computer to a standalone TV set and there was no noise or distortion at the bottom of the screen and the colour bands at the left of the video weren't there either (at least not that I could notice).

So there seems to be some interaction between VHS and capture but I don't understand what it is. Incidentally, the picture from the internal tuner connected to cable, or from the composite out of the VCR, but using the VCR's TV tuner rather than playing a tape, is perfect.

Anyone experience this? Any solution? VHS certainly isn't a great source for DVD transfer to begin with, but the movie isn't available on DVD so I'd like to get as good a capture as possible.

Thanks,
Ric

[trevlac]

Originally posted by ricnews
I hooked up both the other VCR and the one attached to my computer to a standalone TV set and there was no noise or distortion at the bottom of the screen and the colour bands at the left of the video weren't there either (at least not that I could notice).



But can you actually see the full width and height of the picture on your TV? I suspect not. Your TV naturally clips ~5% of the picture all the way around. I believe this would be regardless of whether you are viewing VHS or DVD source. So, you may be trying to solve something that will not be a problem.

Make a DVD with a small sample of your captured VHS and see what happens.

Of course, I may be totally wrong. :) You may be refering to distortions that would actually be viewable on a TV.

[ricnews]

I suspect you're right about the TV clipping some off the edges. I'm guessing the capture card captures the whole image including what's overscanned on TVs and the PVR applications I've tried just don't crop enough out, which makes watching tape on my computer a problem.

I tried virtualdubmod to capture but when I try to put it into preview mode all I see is green. (The image is fine in overlay mode.) I guess I should take a look at the virtualdub faq. I believe it will allow me to crop the edges and rescale. Otherwise I can always crop and rescale post-capture if necessary.

However, the colour distortions I'm seeing at the left edge the screen extend so far to the right they wouldn't be removed unless a very substantial amount of the image is cropped, much more than necessary to mask the distortion at the bottom. (Probably somewhere between 10 and 20% from the left would need to be cropped. This certainly does seem excessive. I wonder if the distortions are only visible on the computer and not the TV though? Maybe I'll do what you suggested and burn a small clip to DVD to see what it looks like on my TV when played from the standalone.

Ric

[mustardman]

The distortion at the bottom of the VCR "image" is due to switching the video heads by the VCR (it has two, one for each field). It will always be there with VHS, and the number of "lines" of distortion will vary (if you play with a VCR - serious & probably destructive playing - you can move this point of swicthing so it ends up a quarter of the way up the screen! This is only possible with old VCRs with adjustments in them). I have seen this vary between about 4 lines and 16 lines. It varies according to both the VCR that recorded as well as the one playing back (mostly due to the playback one).

The colour problem is interesting, and since you don't get it 'off-air', I would suspect the VCR is not playing back correctly.

The "preview" mode of VDub will not help you with this problem, it displays the whole frame - not the "TV safe" frame. This is quite a significant crop, and also varies from TV to TV. If you feel inclined, there is a VDub filter which will draw the TV safe region onto a clip. Apart from doing that it is a pretty ho-hum filter.

MM

BTW, small VHS-C and some full-size VHS camcorders had a smaller drum with 4 video heads on it.

[ricnews]

Hi,

The colour distortion issue occurs when playing VHS to my computer for 2 different VCR units. When playing the same tapes on either of these VCRs to a standalone TV the problem is not there. This is why I think it has something to do with the capture process and not a bad VCR unit.

I also tried burning a clip to DVD to play from a DVD player to a TV. I did not do any cropping and indeed the video displayed on the TV without the bottom distortion. It's just a shame the TV/PVR applications for windows don't give more control over cropping and rescaling.

I also found while the captured video was fairly noisy, it looked much smoother and sharper on the TV. I suspect that's due to the horizontal scan lines masking the noise.

I'm a little surprised at how much noise (grainyness) there is the captured video, actually. My cable reception isn't great so I was never surprised to see it on TV, but I thought there would be less noise coming off a VCR. Is the noise produced at the capture card or the VCR, or both?

I can't get virtualdub or any of its derivatives to capture video. It can display overlayed video, but capture just produces a completely green field. Does virtualdub require VfW drivers or can it function only on WDM drivers?

Thanks.

[mustardman]

Can't really help you with VDub not capturing - sorry.

The colour signal is referenced to a 'colour burst' at the beginning of every scanline. Basically, a crystal in the TV locks to this burst every horizontal sync, and the colour for the rest of the line is derived from comparing the received colour signal with the crystal reference.

If two differnt VCRs exhibit the same problem, and an "off-air" signal doesn't, I really can't say what is going wrong. I would imagine the "off-air" signal has a rock-solid colour burst, and maybe the VCRs aren't providing a good enough signal for the capture card to lock to the colour properly?

One other thing - you have not said if you're capturing PAL or NTSC. There is a very substantial difference in the way the colour works in each system.

[ricnews]

I'm capturing NTSC.

So should those vertical colour bands really be there and they're just clipped off by real TV sets as is the distortion at the bottom or is what I'm seeing really strange?

To give you a better idea what I'm talking about here are a couple of screenshots:

ftp://guest.hipster.dyndns.org:25204/ComproPVR1.bmp
ftp://guest.hipster.dyndns.org:25204/WinDVR2.bmp

Thanks,
Ric

[ricnews]

Here are a couple of screens using input from a different VCR:

ftp://guest.hipster.dyndns.org:25204/02314104.bmp
ftp://guest.hipster.dyndns.org:25204/0514002146_17.bmp

The coloured bands seem to be harder to see in the stills than in the moving image but they're there, although possibly less prominant than with the first VCR.

These are taken from the tuner of the first VCR:

ftp://guest.hipster.dyndns.org:25204/1.bmp
ftp://guest.hipster.dyndns.org:25204/2.bmp

I couldn't see this effect in the stills or the moving video.

Ric

[Arachnotron]

So should those vertical colour bands really be there and they're just clipped off by real TV sets as is the distortion at the bottom or is what I'm seeing really strange?

This should not be there. But I see some color distortion bands in the middle of the picture too.

I'm wondering - could this not be interference in the VCR? Something in the vicinity producing a signal that interferes with the color carrier?

That broadcast is not affected could have something to do with the color carrier for tape being at a different frequency (forgot which). VHS tape uses color under; the chroma is stored separate, shifted to a frequency below the luma range and upon playback it is shifted up again. Broadcast on the other hand is composite, and the complete signal is shifted up to the frequency of the broadcast channel and shifted down again by the tuner after reception. So if the interference is happening while the chroma is still in the 'color under' stage, broadcast would not be affected.

Try the usual for interference: ground everything, make sure your PC case is grounded and closed etc. etc.

[ricnews]

I had thought about interference but then dismissed it because of the good picture from the VCRs' tuners.

I should point out, thought, that the first VCR is located a few feet from the computer, but the second VCR is located in the next room, at least 30 feet away, and connected by a long cable. (The first VCR has a much shorter, better shielded cable.) So the fact I'm seeing this distortion from the VCR in the other room makes me a bit skeptical that it's external interference on the VCR. On ther other hand, if it's interference in the cable or at the computer, shouldn't the tuner image be equally distorted?

It's possible the wiring in the apartment is just shoddy, though.

The other thing is that I couldn't see any of this effect when either VCR was connected directly to the TV (also in the other room).

So I'm not quite sure where to start...

Ric

[Arachnotron]

On ther other hand, if it's interference in the cable or at the computer, shouldn't the tuner image be equally distorted?

Agreed, it does not sound very likely. But try moving the house, just to be sure ;)

Seriously, I have no idea what is going on. I have seen similar banding on VHS, but that was horizontally. In that case the most likely cause was damaged tape, also not very likely here.

[ricnews]

Is it possible this is macrovision? I googled macrovision but couldn't find any pictures showing exactly what it's supposed to look like. Macrovision level 2 and colour burst spiking get mentioned a lot in the same articles, but I'm still not too clear on the whole macrovision thing. The ComproPVR software claims to not allow copying or macrovision protected video and it didn't complain, but...?

Okay, tonight I was at my father's house and tried doing the same thing on his system. So now we're talking a different house (you didn't think I'd actually move it, did you...?), a different VCR, a different computer, a different make/model of PCI TV/capture card, and either composite video or S-video out from the VCR.

And honestly the picture looks much better but after staring at it for a few minutes I started seeing the same thing. It's much less prominant than on my system, but I can definitely detect periodic vertical green stripes, and they do seem to go all the way across or mainly all the way across the picture.

So now I'm really perplexed. Is this just a limitation of consumer capture cards that they can't stably capture a VHS signal or is it some kind of radiation emenating from my body that affects VHS signals?

Since it doesn't seem so likely I'm going to be able to fix this, is there any post-capture video filter that would be able to correct this problem?

Thanks again,
Ric

[Arachnotron]

Okay, tonight I was at my father's house and tried doing the same thing on his system. So now we're talking a different house (you didn't think I'd actually move it, did you...?)
LOL :D :D :D
Is it possible this is macrovision?
I don't think so, this is much to subtle for that.This is not something that would deter the average user from copying. Capcards are not affected by macrovision; they can detect it, after which it is up to the driver or software to either enforce it or to ignore it. When it is enforced you sometimes get no picture at all, or a big white bar, or whatever was programmed into it.

Capping VHS tapes is something standard, many peoplr do it, and you can get excellent results with cards like these.
And honestly the picture looks much better but after staring at it for a few minutes I started seeing the same thing. It's much less prominant than on my system, but I can definitely detect periodic vertical green stripes, and they do seem to go all the way across or mainly all the way across the picture.
What I am wondering about: was this a tape that had ever been in your own VCR? Could it be that one of your VCR's is subtly damaging your tapes, after which they have problems in all VCR's? For instance some part has gotten magnatized or is dirty or whatever?
Since it doesn't seem so likely I'm going to be able to fix this, is there any post-capture video filter that would be able to correct this problem?
If it is stationary, you might be able to treat it as an alpha-blended logo ( = stationary logo that is transparent).
Try Delogo for vdub; the manual can be found here (http://neuron2.net/delogo132/delogomanual/delogo.htm). If it is not stationary, I don't think you can do much that would not also seriously affect the rest of the picture. But maybe someone else has a suggestion.

[edit] Have you tried playing with your VCR's tracking settings?