Drop Out Compensation for Analog Transfers ??

jboy wrote on 12/30/2002, 10:00 PM
I've posted on this before, but after transferring 3 hrs. of 20 year old vhs footage to my computer, I'm again faced with the problem of what to do about the ubiquitous drop outs on almost every frame of video. For those of you too young to know what drop outs are, they're little flashes of white light on the screen that correspond to microscopic imperfections on the vhs tape being played. Pro level hardware, back in the analog days when drop outs were a problem, had built in drop-out compensation built into their electronics. Digital, on the other hand, never has had the drop-out problem, so solutions were never needed.There's gotta be a software fix for this problem. What do the networks do when they restore video tape ? I cant believe they have somebody clean up individual frames in Photoshop ? This might work for a small amount of footage, but for hours worth ? I dont think so.

So again, does anybody know of a software program, that'll remove drop outs from video ? Does anybody know anyone who works in a somewhat high end editing facility, that might know something about this ? In the hardware versions of compensation, the flashes of light were just replaced by adjacent colors, and this should be really easy to do in a software program, (for someone who knows how to do it, of course, not a boob like me ). Anybody, Help !

Comments

craftech wrote on 12/30/2002, 10:20 PM
Vixen or Commotion software will do this if it's worth it to you to invest the money.
If you have Adobe Premier, you could export the files as Premier filmstrip files into Photoshop and paint them out. It will probably take about 12 hours to do all three hours of footage that way.
If you have a digital effects box let me know, because there is a way to do it with one of those as well.

John
David Settlemoir wrote on 12/31/2002, 10:39 AM
Have you tried using another VHS deck? I use to have an Industrial Panasonic SVHS deck with a single-line TBC that would show drop outs from Hell, but when I'd play the tape back in a consumer deck they wouldn't be there, only the image was a tad softer. Also, on older tapes, I always fast forward to the end and rewind before I play them, helps knock off some of the loose particles from the tape.
Former user wrote on 12/31/2002, 10:59 AM
The networks use tape machines with Drop Out Compensators (if it is an analog tape). At our post facility, we still have some 1" and 3/4" tape machines as well as standard Beta SP.

The problem with software might be being able to distinguish between a white line and an actual dropout.

You might be able to rent or borrow a tape machine with a DOC. Some prosumer units have them.

Dave T2
jboy wrote on 12/31/2002, 2:40 PM
Thanks guys. Craftech, do you know if Commotion specifically removes dropouts ? Pinnacles site doesn't seem to be working right and I couldn't get any details on what the program does. Couldn't find anything applicable on Vixen's website either. Do you have arogram name for your recomendation ? I should mention that these dropouts are not of the line variety, but rather small, discrete, flashes of light. I'm sure they're way out of spec for brightness, so a software program should be able to spot em and correct them easily, (he said hopefully)...
jboy wrote on 1/2/2003, 12:17 AM
Craftech, are you out there ?
jboy wrote on 1/2/2003, 12:18 AM
Craftech, are you out there ?
MarkWWWW wrote on 1/2/2003, 7:48 AM
It sounds as though this would be pretty simple to do with a filter via VirtualDub. I'm not aware of any VD filters that are described as "drop-out compensators", but it may be that it would be possible to do it with one of the many image processing filters that are around.

I'm slightly at a disadvantage though because I'm not familiar with the characteristics of these drop-outs - I'm almost entirely an audio person, and when I do work with video it is never with video that was originally on an analog medium. If you have somewhere (Website, FTP server, etc) you could post a few seconds of captured video showing these drop-outs it might be helpful in seeing if it is the sort of thing that a VD filter might be able to handle.

Mark
jboy wrote on 1/3/2003, 2:50 PM
Wouldn't be worth the effort to upload examples. If you want to see what I'm talking about, just put any commercial vhs tape into your vcr, and play the first 30-sec to 1 minute, the black leader part. They invariably contain these kinds of dropouts, owing to how tightly the tape is wound around the hub at this point. It's also why you have this black leader portion.
MarkWWW wrote on 1/4/2003, 4:10 AM
Hmm, I've just tried playing the black lead-in of a few of my commercial VHS tapes and I don't see anything like your "little flashes of white light" description on any of them. Perhaps my video recorder is suppressing them.

I still suspect that this is the sort of thing that could be dealt with by a suitably designed VirtualDub filter, but without having seen the problem for myself I can't say for sure.
jboy wrote on 1/4/2003, 12:19 PM
Maybe your vcr has effective drop out compensation built in. Try to find an old, crappy, vhs tape that's been played a lot. That should have some drop outs in it, (unless your built in dropout compensator is so effective that it masks even these). Really, these things are quite unspectacular. They're just little flashes of light that occur when the vcr head passes over an area of the tape thats has the oxide coating damaged, and the vcr head reads this as a maximum, (I'm sure totally off scale), white light.They kind of look like static on an over- the -air received tv signal, only they're not as organized into a pattern,or as numerous as in this example. Can VirtualDub create a filter that'll suppress brightness values above a certain level, and replace the too bright area with adjacent pictorial content or color ?
MarkWWW wrote on 1/5/2003, 10:10 AM
> Can VirtualDub create a filter that'll suppress brightness values above a certain > level, and replace the too bright area with adjacent pictorial content or color ?

I'm not a programmer (these days, anyway) and I've never seriously investigated writing a VirtualDub plugin for myself, but on quickly looking through the VirtualDub Filter SDK it would seem that replacing values above a certain threshold with the average of adjacent values would be pretty easy.

I'm pretty sure that this is the basic technique used by many of the existing noise-reduction filters.