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Old 4th August 2003, 10:37   #1  |  Link
t610425
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Color areas overflowing at VHS Captures

Hello everybody,

I'd apreciate your advice on the following:
I;m using a PCTV Rave cap card (and an Avermedia also for NTSC) and Virtualdub VCR+sync to capture VHS tapes.
Compression is PICVideo MJPEG @ 19 quality.

BUT the colour is overflowing in the captured frames. This is most obvious with red or blaze orange colours.
Is there any way to deal with this.

I attach a jpg since 1 pic is worth 1000 words!

Tnx in advance,

All the best

Takis

Hmm.. I would attach a jpg if I had permission!
so pls see http://users.otenet.gr/~dataplex/VHS-Capture.jpg for the image.
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Old 4th August 2003, 14:46   #2  |  Link
Wilbert
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Could you upload a short clip somewhere?
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Old 4th August 2003, 17:32   #3  |  Link
t610425
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Quote:
Originally posted by Wilbert
Could you upload a short clip somewhere?
Of the capture (ie MJPEG ompression)?
Well I tried but a 2" clip is ~ 64MB and I don't have enough MB quota to store it!, will DivX do? If yes:
http://users.otenet.gr/~dataplex/vhs-capa.avi
For some reason MPlayer will not download it, but I verified that zoomplayer will.
Divx settings Qbased @93%

atb

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Last edited by t610425; 4th August 2003 at 18:05.
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Old 4th August 2003, 18:21   #4  |  Link
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I ran the source through AviSynth's SeparateFields() filter. The problem appears in the individual fields. It is either in the VHS source, or from capture card driver settings.

By the way, this video sample (and the .jpg you initially showed) need deinterlacing.
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Old 4th August 2003, 19:25   #5  |  Link
t610425
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Quote:
Originally posted by jggimi
I ran the source through AviSynth's SeparateFields() filter. The problem appears in the individual fields. It is either in the VHS source, or from capture card driver settings.

By the way, this video sample (and the .jpg you initially showed) need deinterlacing.
It must be the source, since it also shows up in the TV. Is there any way to remedy this?

Why deinterlace? I just back-up VHS tapes to DVD. I think deinterlacing actually makes a differemce if you view output on a comptuter monitor.
Actually it seems that an enormous efford is going on towards deinterlacing, but does one need to deinterlace if the output is suppossed to play on a TV?
I'm asking since I only mess with video editing for a couple of months.

Tnx in advance,

atb

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Old 4th August 2003, 19:44   #6  |  Link
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This Chroma-bleeding is normal, when dealing with VHS.
VHS stores the Chroma Inforation with a heavy decimated bandwidth.

Another thing is, that VHS shifts the chroma down vertically by two lines (everytime!) and sometimes horizontal.
This horizontal chromashift depends on the VCR used and may vary from tape to tape.

Two help a little bit against this bleeding/shifting, there are a few Filters:

for AVIsynth, use "chromashift.dll"
and
for VirtualDub use "flaxens VHS-Filter"

I've played a little bit with the chroma, and found
horizontal right-shift by 4 pixels
and
vertical up-shift by 2 pixels
useful.
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Old 4th August 2003, 20:21   #7  |  Link
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And you're right, for display on interlaced devices like TVs, when using an interlace capable codec (like MPEG-2), the only reason to deinterlace would be to reduce bitrate consumption.
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Old 4th August 2003, 23:41   #8  |  Link
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Quote:
Originally posted by scharfis_brain
This Chroma-bleeding is normal, when dealing with VHS.
VHS stores the Chroma Inforation with a heavy decimated bandwidth.

Another thing is, that VHS shifts the chroma down vertically by two lines (everytime!) and sometimes horizontal.
This horizontal chromashift depends on the VCR used and may vary from tape to tape.
Whoa! Is there a good discussion of this somewhere in the forum? I'd like to understand this.
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Old 5th August 2003, 00:35   #9  |  Link
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@Fred: I'm not sure, wheather you're doing irony or not....

if not, please specify, what do you want to understand
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Old 5th August 2003, 07:29   #10  |  Link
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Irony because of all the talk about chroma problems with DV? No.

No, I'd like to understand how to determine when and how to correct chroma shift from NTSC VHS source. The VCR I use is a JVC HR-S7600U and it's got various TBC and digital filters. Those help a lot but I don't think they will do anything to correct problems in the source. IOW, If a tape was copied from a tape without correction, the chroma would be positioned incorrectly but the VCR's filters wouldn't know that.

The process of properly re-locating chroma on the frame is what I do not understand.

Also, any filtering such as CNR for VirtualDub is somewhat of a puzzle to me. It's got a lot of settings but I have no idea which to tweak and why.

I understand many of the principles but don't feel I am proficient with correcting problems from VHS source. Whenever possible, I prefer to use AviSynth instead of VirtualDub because my capture is primarily MPEG2 hardware (ADS Instant DVD 2.0) or DV (Canon camcorder passthrough) and destination is MPEG-2 as either XSVCD or DVD.

That's why I'm asking if there is a good how-to thread already. Certainly, I'm interested in learning. If you would provide some guidance, I'd appreciate it.
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Old 5th August 2003, 09:23   #11  |  Link
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There's also a hardware fix you can try. If your capture card is up to it!

Quote:
This Chroma-bleeding is normal, when dealing with VHS. VHS stores the Chroma Inforation with a heavy decimated bandwidth
If your outputting and capturing using composite. There is a little connector you can get which converts a composite output to S-VHS output. The connector costs no more than 5.00. Maybe your card has an S-VHS input!

Now, let me stress. This is a cheat. It only works on 'some' occasions and with 'some' cards. As it all depends on how clever (unclever really) the card is.

I think it would be pointless to ramble on about the differences between a true 'composite signal' and 'S-VHS' signal. And even more pointless discussing how you can fool an composite signal into thinking it's an S-VHS signal.

Some of these tricks should'nt work. But sometimes they do - It's only because I'm an obsessive, compulsive fiddler. That I know that they do!

Hope that make sense. Cheers.
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Old 5th August 2003, 10:23   #12  |  Link
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@Fred: those values for shifting chroma, i've only got by testing, "what looks best". After a while I found out, that every generation of VHS-copy introduces a new vertical shift by 2 lines.
so, a copy from VHS->VHS has already chroma shifted by 4 lines.
The same with horiz. shift. You have to try to relocate the chroma using your eyes, but this isn't very easy, because of the bleeding....

@SeeMoreDigital: Not, its NOT the Composite-Connection. Its the VHS, that is the reason for the bleeding chroma.
VHS strores LUMA with about 2,5MHz bandwidth, and the CHROMA is stored with about 0,6 MHz, so there are about
240 lines of LUMA you can store
and
60 lines of CHROMA. I hope, you'll see it now, why chroma is bleeding horizontally on VHS...

@all: I am talking about PAL-VHS. I don't know wheather NTSC-VHS will introduce the vertical shift, too since I am already able to deal with PAL60 and not with real NTSC. With using PAL60 (on NTSC-Tapes) the vertical shift is also there, like when using true PAL-VHS. All other things should be the same.

EDIT: please take a look at this: http://www.gthelectronics.com/featurec.htm
I think they described it very well... (color bleed and color droop)

Last edited by scharfis_brain; 5th August 2003 at 10:31.
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Old 5th August 2003, 11:00   #13  |  Link
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Quote:
Originally posted by scharfis_brain
@SeeMoreDigital: Not, its NOT the Composite-Connection. Its the VHS, that is the reason for the bleeding chroma.
VHS strores LUMA with about 2,5MHz bandwidth, and the CHROMA is stored with about 0,6 MHz, so there are about
240 lines of LUMA you can store
and
60 lines of CHROMA. I hope, you'll see it now, why chroma is bleeding horizontally on VHS...
It would sound like you've never had the opportunity to try what I've suggested.

If not please humour me, by having a go at outputting a high red composite VHS tape source image and then capturing it to an S-VHS tape player/ouput - using one of the 'comp to S-VHS' adaptors I'm talking about.

It helps most times with VHS tape to S-VHS tape dubs. But not all the time with VHS tape to S-VHS capture card dubs!
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Old 5th August 2003, 11:18   #14  |  Link
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Quote:
Originally posted by SeeMoreDigital
It would sound like you've never had the opportunity to try what I've suggested.

If not please humour me, by having a go at outputting a high red composite VHS tape source image and then capturing it to an S-VHS tape player/ouput - using one of the 'comp to S-VHS' adaptors I'm talking about.

It helps most times with VHS tape to S-VHS tape dubs. But not all the time with VHS tape to S-VHS capture card dubs!
Anyway FYI I use SVHS connection. What I've noticed is that this problem increased logarithmically when the tape quality deteriorates.

Since we are at it could somebody explain why red seems to be more prone to bleeding?

tnx

atb

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Old 5th August 2003, 11:26   #15  |  Link
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I've also tried a true S-Video connection from a VHS-C-Camcorder to my WinTV Card (my VCR has no S-Video and I don't want to by such Comp->S-Video adapter, since I am satisfied with my results). The Chroma bleeding was exactly the same. But the image was a little bit sharper. But the chroma wasn't.
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Old 5th August 2003, 15:25   #16  |  Link
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Composite - S-Video (S-VHS) adapter... Come on.. You know how you can split one line? That adapter maybe has some freq. filter, but same filter must be in capture card, as in every TV.
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Old 5th August 2003, 15:51   #17  |  Link
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Could someone recompress that avi for me? XviD Q100 is fine. If I open it in vdubmod (using DivX5.02 as decompressor) the first frame shows up correct while the rest is green
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Old 6th August 2003, 10:53   #18  |  Link
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Quote:
Originally posted by ppera2
Composite - S-Video (S-VHS) adapter... Come on.. You know how you can split one line? That adapter maybe has some freq. filter, but same filter must be in capture card, as in every TV.
Have you forgotten that on a 'scart plug' the chroma connection is on 'pin 15'. What else is on 'pin 15'? Oh, that would be the RGB 'red' input then!

And also by introducing 'resistance' on the chroma you can cut down on the red over flare. As I said before, it's a cheat - nothing more!
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Old 6th August 2003, 12:07   #19  |  Link
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SeeMoreDigital:

We talking here about composite-S-VHS adapter. Why you talk now about extended SCART connection for S-VHS? This is not composite anymore.

However, decreasing chroma level, while leaving luma intact could be good in some cases. But it can everybody make himself, and even adjust best resistance with variable resistor (potentiometer).

Must say that I never had similar problem with PAL VHS tapes, although I captured from lot of very bad quality.

Last edited by ppera2; 6th August 2003 at 12:10.
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Old 6th August 2003, 15:40   #20  |  Link
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Quote:
VHS strores LUMA with about 2,5MHz bandwidth, and the CHROMA is stored with about 0,6 MHz, so there are about
240 lines of LUMA you can store
and
60 lines of CHROMA. I hope, you'll see it now, why chroma is bleeding horizontally on VHS...
luma: 3,0 MHz, 40 lines of chroma. See http://www.cs.tut.fi/~leopold/Ld/VideoFormats.html

Apperently this color bleeding varies from vcr to vcr. What is the exact reason for this? Poor filters? What kind of filters are used to reproduce the color in the correct position?
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