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t610425
4th August 2003, 11:37
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.

Wilbert
4th August 2003, 15:46
Could you upload a short clip somewhere?

t610425
4th August 2003, 18:32
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

takis

jggimi
4th August 2003, 19:21
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.

t610425
4th August 2003, 20:25
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

takis

scharfis_brain
4th August 2003, 20:44
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.

jggimi
4th August 2003, 21:21
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.

FredThompson
5th August 2003, 00:41
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.

scharfis_brain
5th August 2003, 01:35
@Fred: I'm not sure, wheather you're doing irony or not.... :rolleyes:

if not, please specify, what do you want to understand

FredThompson
5th August 2003, 08:29
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.

SeeMoreDigital
5th August 2003, 10:23
There's also a hardware fix you can try. If your capture card is up to it!

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.

scharfis_brain
5th August 2003, 11:23
@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)

SeeMoreDigital
5th August 2003, 12:00
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!

t610425
5th August 2003, 12:18
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

takis

scharfis_brain
5th August 2003, 12:26
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.

ppera2
5th August 2003, 16:25
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.

Wilbert
5th August 2003, 16:51
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 :(

SeeMoreDigital
6th August 2003, 11:53
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!

ppera2
6th August 2003, 13:07
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.

Wilbert
6th August 2003, 16:40
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?

FredThompson
6th August 2003, 19:04
ePanorama might have some useful circuits: http://www.epanorama.net/links/video.html

This is starting to get very interesting. I wonder if there's an inexpensive circuit to allow some chroma level fix without any quality degradation. Chroma shift would be much more difficult.

I'd love to have one of those processor boxes mentioned in another thread but $500 or so is a bit much for me.

SeeMoreDigital
6th August 2003, 20:03
Originally posted by ppera2
We talking here about composite-S-VHS adapter. Why you talk now about extended SCART connection for S-VHS? This is not composite anymore.
I was using an analogy, as to where the chroma part of an S-VHS signal is biased i.e the red.

You can purchase one of these connectors from www.lektropacks.co.uk Order ref code P-SCON Cost 6.60 or you could make one yourself!

Freds idea is an interesting one indeed and could be useful when you consider that both the luma and chroma frequencies are by no means fixed!

I'll have to get my soldering iron out and test some designs using different VCR's.

FredThompson
6th August 2003, 23:05
A brief scan of ePanorama doesn't really show a lot. There IS a TBC circuit but it's not so easy to build. There was a magazine called Radio-Electronics which had lots of TV stuff years ago. Maybe we can find some old schematics...

SeeMoreDigital
6th August 2003, 23:53
Thanks Fred

I remember building a very simple circuit similar to what we want now about 15 years ago.

However I ditched it in favour of a more complicated 'off the shelf' unit that had plethera of functions.

Unfortunately this device has long since gone to black box heaven so I'll have to get my thinking cap on.

Trouble is I can't think where I've put my cap either!

But I do just happen to have boxes full of half cut and spliced cables with all manor of electronic components soldered to them.

I'll sort something out though. Which will probably be fine for what I want but be totally useless for anybody else's requirements!

torsius
7th August 2003, 01:27
There is a very simple way to decrease the amount of "bleeding" of the color associated with VHS when capturing. I'm very picky about how my vhs rips look, so I imagine this fix will help you out.

I recently noticed this "bleeding" effect on a 10+ yr old vhs of an old Garfield recording (garfield is blazing orange btw)

In order to clean up the nasty bleeding, i merely decreased the saturation level of the capture source (the capture program I use allows direct adjustment of brightness, contrast, saturation, gamma, etc on the capture driver)

I think the saturation is kinda like an audio clip that has reached distortion level, so you just turn it down a bit :)

hope this helps

FredThompson
7th August 2003, 03:27
yeah, that's basically what an external box would do. It still boils down to GIGO but maybe, just maybe, there's something to be gained from a little black box. ePanorama has some schematics for edge detect/sharpening and things like that. I'm pretty convinced there isn't an easy way to remove bleed that's in the picture, just wondering if something might be gained by a little dongle. Many moons ago, in a discussion I barely remember in alt.binaries.multimedia.vintage-film there was discussion about using baluns to wipe out ground loop noise, 75 ohm to 300 and back to 75 or something like that. I might still have copies of those discussions...

Actually, I know a good person to ask there...

t610425
7th August 2003, 05:53
@wilbert: Sorry but I don't have xdiv installed, could somebody else help?
@torsius I'll try this tnx

scharfis_brain
8th August 2003, 10:58
@t610425: Have you tried to shift the chroma, too?