New Filter Idea

[slk001]

Gentlemen (and Ladies?),

I have an idea for a new temporal filter. When I capture from a slightly scratchy laserdisk, I get what I call "silver streaks" streaming across the screen. This is caused by the laser losing focus for a brief (but noticeable) period. Because of the nature of the laserdisk (and television) scanning, these streaks are never more than 1 pixel wide nor on more than one field (from THAT scratch, anyway) and always run horizontal. I have attached a file showing three consecutive fields which shows a streaker in action.

Could a simple filter be written that basically says, given pixel 255 on field A, B and C, IF P255 on A is within a threshhold of P255 on C, then P255 on B should also be within this threshhold. If P255 on B is NOT within this threshhold, then replace P255 on B with AVG of A P255 and C P255.

I've tried both temporal and spatial smoothing to eliminate these, but to completely eliminate them results in a lot of picture bluring.

Maybe this can be accomplished by using already existing filter. If so, can you suggest a script?

The pictures attached came from a movie captured directly to MPEG2 at 9Mbps, then frameserved to VirtualDub where an IMAGE SEQUENCE was generated. I usually re-encode my captures using VBR in CCE to reduce my space requirements.

Comments?

P.S. This filter would also have the tendency to remove all SUBLIMINAL MESSAGES embedded within a video stream!

[slk001]

Here's the attachment.

[slk001]

The board doesn't like a .jpg file. Here's a .bmp version?

edit by dividee: attachment deleted. The board like jpg more than bmp, but attachments have to be validated before showing up.

[trbarry]

You could probably do something similar with STMedianFilter but if you turn it up high enough to get rid of the extreme streaks then it will probably also tend eat single pixel wide lines or create ghosts.

But see www.trbarry.com/STMedianFilter.zip

Note the recommended parms in the readme file are for fairly noisy source, but haven't been updated. For new folks trying this to do a touch up with fairly clean source I'd recommend something more modest like:

STMedianFilter(8,15,5,7,8,15)

At the time I wrote the readme I hadn't done much testing on clean source yet. But for your case you might want to crank up the first 4 numbers and see how high you can get removing the streaks before you get other objectionable artifacts. Specifically, the very first number is the maximum amount that a pixel value will be changed by spacial filtering (except horizontal). If it would be changed more than this than it will be left alone. The 3rd parm does the same for temporal filtering. (0-255)

Be aware this is all fairly new and untuned yet.

- Tom

[droolian01]

Hi slk001 and all,

Are you sure that these streaks are caused by the laser loosing focus? I used to get exactly the same streaks when capturing from a digital cable stb via s-video. It only occured when the data rate was too high for my relatively poor spec system (so i couldn't use huffuv at any decent resolution, or pic mjpeg full d1 @19). If the % cpu shown in vdub capture mode was consistently >50%, although i would only get a very occasional frame drop (probably for audio sync purposes anyway) these lines would appear.

I remember reading on the vdub homepage ages ago that it was thought that bt8xx capture card buffers get maxed out and thus lose a line. Something like that.

So if you are using a brooktree bt8xxx tv card this could be your problem - just reduce the data flow b reducing res or using mjpeg.

Hope this is useful

[poptones]

The streak show above is a buffer problem not a laserdisk problem. However, I also have seen the laserdisk problems he mentions, and if I weren't so lazy I'd load up an old Siouxsie and the Banshees cap I made from LD and post it. The laserdisk errors are usually very short and look a bit like a white horizontal "gouge" from the video.

They also trail off rather than make abrupt transitions, which means you need a way to locate the "front" of the hole, then gradually blend your repair back out as the video returns to proper levels.

[slk001]

This streak IS a laserdisk read problem (you can see the scratches and almost predict when they will start appearing). The picture above has a resolution of 140x50 pixels, which includes the streak entirely. There are others in this area on the LD, but this one is typical. There are no missing lines.

I also don't capture using VirtualDub, but I use a real time MPEG2 capture card (at 704x480). This card does everything in hardware, so it doesn't tax the system at all (<10% resources, mostly disk accessing).