Fixing or minimizing problems from bad tape

2G wrote on 10/16/2004, 5:19 PM
I apparently got a bad tape. It was a Sony Digital8. In the captured video, there are random pixel flashes over the picture (freeze framing on certain frames show tiny blocks of various patterns and x's, etc. Also, the audio pops. Expanding one of the pops shows the audio flat-lines for one frame count, then starts up again.

Just to make sure it was really on the tape, I captured a segment a second time and lined the two captures up on the timeline. The audio dropouts occurred identically on both captures.

I've used the camera since then and had no problems. So it pretty much points to the tape.

But my question is now, given the problem, is there anything I can do to repair it? I've got the audio from a separate camera, so I really don't need to fix the audio. But I really would like to minimize the bad pixel boxes on the video.

Is there any software or filtes that can minimize the visual problem? It is a stationary camera at a wedding. So there is very little movement in the video. Something as simple as merging every other frame might help.

Just curious if there is any hope.

Thanks.

2G

Comments

farss wrote on 10/16/2004, 6:13 PM
If there's no motion in the shot then you could just patch frames. If there is minimal motion and you want to save time then motion blur can do a pretty good job.
You could also try playing the tape back in a D8 camera or VCR as they do a better job. I'm curious though, how did you get from the Hi8 camera to firwire?
If you're going out to DVD believe me those one frame flashing blocks get much worse after encoding. Do anything to try to smooth them out a bit before encoding.

Bob.

2G wrote on 10/16/2004, 7:57 PM
It wasn't Hi8. It was D8 all the way. D8 tape in a D8 camera. Captured using the same camera as it was shot on. Manual patching isn't practical since it happens about once every second or two for a 40 minute wedding.

I'll try motion blur to see if that helps. Seems like there ought to be something out there that could detect and fix. Any time there is a block of pixels that's green for 80 frames, white for one frame, then green for 80 more should be detectable given appropriate access to the data stream... which I don't have... :-(
musicvid10 wrote on 10/16/2004, 8:05 PM
JFYI,
If you fast forward and then rewind the tape in your camera before you record, it will reduce possible tape drag and tracking problems caused by stiffness in the tape casette.
johnmeyer wrote on 10/16/2004, 11:16 PM
Try capturing on another camera, if you can. Sometimes the tape will read on one camera, but not on another, and vice versa.
farss wrote on 10/16/2004, 11:46 PM
One trick from the guys on another forum, copy from one deck to another, the theory is that capturing is more critical than making a straight copy. I know it's hard to believe BUT I've rescued stuff by capturing the analogue output from a DV VCR.

Of course the most obvious things to try first:
1) Clean the heads.
2) Try tape in another device. Don't have much choice with D8 although there is a D8 VCR, I'm suspecting it has the same transport and heads as the cameras.

I agree, you'd thing there'd be some smarter tools out there, there's a general lack of widgets that work accross frames apart from high end stuff used by the big boys. I cannot see why they cannot release these tools as non realtime software using the same algorithms. S&W make some truly wonderful restoration boxes that costs more than a house, fair enough the hardware is expensive and they must have a lot of R&D to recover but it seems to me they'd sell a bucket load more if it was say 5% of the price for the software version.
Maybe this is a true conspiracy, heaven forbid if us lowly plebs could do all those wonderful things, the big end of town would be cut down to size.

Or maybe, just maybe this is another example of how we all get screwed by piracy, hardware is much easier to protect but even that's a two edged sword, if the algorthims get leaked then anyone can put out a freeby version as code only and then their market is totally blown away.

Bob.

2G wrote on 10/19/2004, 11:48 AM
Thanks for all the suggestions. I'll see if I can borrow another D8 camera to try recapture.

For now I've been playing around seeing if I can minimize the effect. I duplicated the entire track on a track above the original. On the top track, I offset the entire video clip by one frame (since the flashes are single frame, and since there is minimal action on the video). I then cut the alpha on the top channel to 50%. So basically I get a two frame pixel flash, but both frames are 50% bad pixel mixed with 50% correct pixel. Seems to look better. But I haven't done the full render to DVD yet.

Thanks again.

2G
mcgeedo wrote on 10/19/2004, 12:41 PM
There is a "temporal smoother" filter for VirtualDub. It averages pixels across frames. I've used it a few times and it does a pretty good job of reducing noise ("snow") in analog tapes. It just might help you out, and it is basically free. It's worth a try, anyway.
farss wrote on 10/19/2004, 3:39 PM
Motion Blur does much the same thing but you have more control via an envelope. Also the project wide settings control how it is applied. For normal motion blur the default (symetric) is wrong but would be ideal in this situation.

Bob.

johnmeyer wrote on 10/19/2004, 6:53 PM
If you want to play around with AVISynth, it has a wonderful filter called Despot that is designed to remove dust spots. Here's a sample script:
loadplugin("c:\Program Files\AviSynth 2.5\plugins\despot.dll")

AVISource("D:\myvideo.avi")

converttoYV12(interlaced=true)

DeSpot(show=0,p2=2,mthres=9,p1=18,pwidth=20,pheight=20,mwidth=4,mheight=5,interlaced=true,merode=28,ranked=true,p1percent=0,dilate=0,fitluma=true,blur=4,motpn=false,seg=0)
Set pwidth and pheight to the pixel size of your dropout spots.
2G wrote on 10/20/2004, 9:21 PM
Do you have a URL for VirtualDub?
2G wrote on 10/20/2004, 9:21 PM
Thanks. Is AVISynth part of the base Vegas package? I'm not familiar with it
mcgeedo wrote on 10/21/2004, 6:12 AM
www.virtualdub.org for the basic application.
neuron.net for a good selection of filters.
www.alparysoft.com/prod/denoise.php is an excellent temporal noise filter.
johnmeyer wrote on 10/21/2004, 6:48 AM
Thanks. Is AVISynth part of the base Vegas package? I'm not familiar with it

It has nothing whatsoever to do with Vegas or Sony. It is a separate, third-party freeware program.