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Old 20th December 2011, 16:44   #1  |  Link
nhope
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Remove sharpish vignetting (black corners)?

A lot of my underwater PAL DV footage has black corners where the edge of the lens/port are visible. In most clips it is only on the left side. On a few it is on both sides. The size of the vignetting varies a little with time because of auto-exposure and in-camera image stablisation.

Here is 2 seconds of typical PAL DV source. And here is a screenshot:



In the past I've repaired this in Sony Vegas by masking off the corners, copying the clip to a lower track, and moving it to the left so that the footage immediately to the right shows through. In some cases the result is pretty good:



In other cases not so good:



And in cases where there is detail next to the corner, it just doesn't really work, although arguably it's still less noticeable than ugly black corners:



I'm wondering if anyone has a better way to repair this sort of thing? Obviously the last example is near-impossible, but for the open-water shots it would be great if there was some way to read the first "clean" pixels around the corner and then paint those over the darkened corners... Or perhaps some sort of inverse barrel distortion? Ideally I don't really want to just crop the footage.

Thanks!
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Old 20th December 2011, 16:55   #2  |  Link
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Vignetting can be repaired, but in your case there is a lack of image, and no software can ever guess what was supposed to be there. There are however several approaches, one of them is used in some delogo scripts, which uses the inherent panning of the camera to borrow parts of the previous/next images to fill in the missing parts of the current image.

Since it's DV I would simply black/crop the margins, they won't be anyway seen due to the analog overscan (also present on flatscreen TVs).
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Old 20th December 2011, 17:25   #3  |  Link
nhope
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This footage has already been on DVD without repair, and you're right, overscan means it can't be seen. I'm addressing it now because it's going on the web and it's more bothersome. Quite a lot of straight cropping would be needed to get rid of it. I would prefer my existing crude repair method to that.

I think a spatial is probably the way to go, not temporal, since the same part is affected in surrounding frames.
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Old 20th December 2011, 17:33   #4  |  Link
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If the mask was feathered, those repairs would be less obvious.

Video inpainting algorithms are temporally unstable and somewhat unpredictable. Potential artefacts would be more distracting than black corners IME. You might be lucky. If there's lots of movement, motion compensation to fill in the missing bits might work better.

Where it's darker, but not black, a masked graduated luma change would help. That would leave a smaller area to repair (what ever method you choose for the repair).

Cheers,
David.
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Old 20th December 2011, 18:46   #5  |  Link
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Actually, feathering the mask makes it more noticeable. At least the way it works in Sony Vegas. The feathered part adds to the luminance, rather than blending at the same luminance. The compositing mode of the upper track is set to "Source Alpha" (default). None of the other numerous available compositing modes help. In some cases, making the feather enormous can help. I'll see if anyone on the Vegas forum can help with that.
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Old 21st December 2011, 07:58   #6  |  Link
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If you are not bothered about the way this video looks in a regular TV, and since you're planning to put it on in internet, why don't you simply crop the image?

It's extremely fast, you don't care if the image is something like 656x540 (instead of the regular PAL/NTSC 720/704x576/480 framesize) and the image to be seen is anyway the one you filmed (except for really pro gear, all the camcorders actually display the overscan image in the control monitor) - I mean if you used the control monitor to frame the subject, the image you have seen and used to frame the subject, ie zoom, pan etc., is actually the one you'll get after cropping.
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Old 21st December 2011, 08:44   #7  |  Link
nhope
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I take your point, but I would rather retain the whole frame despite it showing information that was not there in my viewfinder. The footage is also going to a revised version of the DVD, so from a workflow perspective, it's easier not to crop only the web version.
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Old 21st December 2011, 08:53   #8  |  Link
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Black the borders then, on a DVD they won't be seen anyway (provided you blacked the correct amount, max 5+5%).
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Old 21st December 2011, 08:59   #9  |  Link
nhope
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My DVDs often get viewed on computers where overscan does not apply. And I don't really want blacked borders on the web versions. Thank you for your suggestions. I appreciate them.

Even if I blacked the borders, I have a few clips with more severe vignetting that would protrude beyond the borders, so I am interested in any inventive ways of repairing it. But it's starting to sound like my existing method is probably the most suitable.
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Old 21st December 2011, 09:19   #10  |  Link
nhope
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In case anyone was wondering, I solved the problem of the paler halos I was getting when feathering the bezier mask that I was using for my repairs. See http://www.sonycreativesoftware.com/...ssageID=792681.
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Old 21st December 2011, 09:23   #11  |  Link
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probably a similar solution with after fx (two handmade masks with feathering and additional or screen blending of masked layer)


(i also did slight upsizing, since you need to get rid of some colorful bars at the top and bottom as well)
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Last edited by smok3; 21st December 2011 at 09:34.
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Old 21st December 2011, 10:45   #12  |  Link
nhope
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Thanks smok3. Indeed that's a similar repair concept. Thanks for reminding me to crop a couple of lines off the top and bottom for the web version.
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