Any way to fix warped film?

[Lyris]

I'm dealing with film material right now where during the first reel, the film seems to "snag" and bump slightly in the telecine gate. The effect is a slight "bump" which lasts for a few frames. It's rhythmic, so it's a little distracting - you know when it's about to come.

I've tried using Photoshop to fix the issue as best I can, but the problem is, the amount of distortion is not linear across the entire frame. That is to say, the top is a bit more stretched than the bottom, etc.

Does anyone have any solution for this? The only fixes I know of are on the megabucks restoration workstations which I don't have access to. It doesn't have to be Avisynth-based but thought this was a good place to ask :)

I'll post a sample later today.

[Mug Funky]

get the film transferred on a pin-registered scanner, like an Arriscan.

capstan-servo film transports will do this. as a bad splice goes over one of the tension arms, it pulls the film back in the gate, and on the way out when it goes over the other tension arm, it pulls the film forward in the gate. as the scanner requires constant motion to give you the vertical component of the picture, you get these bumps when the speed varies.

if it's old, shrunken film, it might be worth getting it cleaned and possibly re-spliced - this reduce the bumps as the splices will be cleaner. this is pretty expensive though.

as far as fixing the footage you have digitised already, i'd say a temporal median could help somewhat by just removing the sudden changes, but i'd rather not do anything that severe. mesh-based motion compensation could also help if you could get the right settings (maybe reconstruct the wobble frame from the neighbors, then compensate the wobble on top of the interpolated frame?)

[Lyris]

Unfortunately finding the original film source isn't an option in this case - something I'm not happy about. Our only option is to do the best with the 1996 transfer that we already have (and thanks to AVISynth, it looks a hell of a lot better than what went in, at least). Will look into what you suggested, thanks!

[Dogway]

Its the same issue I had recently. I made a thread for that. film gate wave/shaking in part of frame (http://forum.doom9.org/showthread.php?t=154283) I also had jitter, but read the overall thread, I pointed another alternatives like UnwrapJ, etc

[Mug Funky]

not sure how you can know that without seeing a sample. analog can do some weird things, some which can share similar descriptions.

i think we need a sample :)

[Lyris]

Here you go. Don't worry about the videotape noise and off colour... that has been taken care of already!

Lagarith .AVI 6mb:
http://www.sendspace.com/file/j2xgqo

[Mug Funky]

aaah, that old chestnut. lemme guess, this happens near cuts, or does it happen in a periodic way? i can't tell from a short sample.

from the look of it (film is very clean) i'd say you'll be getting a wobble pre/post scenechanges rather than periodically (gradually speeding up as the film plays, then repeating the pattern every reel). reason being, if it was the film snagging, you'd see crap all over it. if the film is clean, then the bumps will be splices - this is probably a roll of cut negative, so the cement splices will pull as they go over the tension arms on the telecine (this looks very familiar to me. was it transferred on an Ursa Gold or Diamond to betacam SP?).

as far as removing it... not too sure. a custom warp could be developed if you have enough time. if you're lucky, the bumps will come a predictible and deterministic number of frames from the cuts, so you could detect the cut and modify frames x and y frames from the cut.

[Lyris]

It's not just near cuts actually, it's for the first 5 minutes or so of the first reel - and it happens in the middle of scenes, too - so that rules out the cement idea.

Yes, the master was Beta SP - that vintage :) The telecine was some sort of CRT-based machine, so your guess of Ursa is better than mine!

[Mug Funky]

hmm. the reels could be out of whack - if it were me transferring it, i'd wind the film through first (slowly) to get the spools to behave and get an idea of the film's condition. if it's still wobbly after a wind-through there's not a lot that can be done - motion compensation might help you, but parts of the frame will remain wobbly.

it's not the worst i've seen from a CRT capstan-servo based telecine... they can get much worse when the tube is dying (think sine-wave horizontal offsets, so verticals become waves, and the waves oscillate about 1 cycle per minute so you only see it in fast forward)

[Lyris]

I wish I had access to the film, I'd have it telecined again. This was a 1996-ish job and it's all we have to work from. Looks like this is one of the few defects that will have to remain - fortunately it's infrequent.

[poisondeathray]

Here is my quick attempt for fixing telecine warp repair using Nuke.
http://www.mediafire.com/?o2dwmthmfx2

The basic approach was to reconstruct the offending frames from predictive motion vectors using surrounding "good" frames.

If you examine frame by frame, you can see some residual prediction errors, but they are not really noticeable at regular playback speed. If you wanted to spend more time, you could tweak it and get almost perfect results by compositing it and using masks.

You can use Nuke or Mokey to do telecine warp repair. If you don't have access to this software , check your local university's computer graphics lab they might have software you can use.

I'm wondering if you could use avisynth to do something similar with prediction and replacing frames / or parts of frames? Perhaps mvtools?

[Dogway]

@poisondeathray: roughly what nodes did you use? just plain compositing/masking?

[poisondeathray]

@poisondeathray: roughly what nodes did you use? just plain compositing/masking?

Mainly frame repair ; I didn't use a matte for the motion vectors (which would have improved the accuracy) .

I used match grain afterwards (the frame repair tends to yield frames without grain ) , and with match grain I ended up using a mask for the shadow area in the lower left

Some compositing had to be done because frame repair prediction isn't perfect.

I'm thinking something like MVTools might be able to do something similar , something like MFlowFPS to generate "in between" frames . The compositing part would be difficult to do in avisynth alone, however

EDIT: I played with MVFlowInter() from MVTools2 , and does ok generating the replacement frames . I replaced 12, then 11+13, then 14 straight from the documentation examples. I'm sure more experienced folk could tweak the parameters better
http://www.mediafire.com/?k1m5vzkhdnk2tz4