Progressive film footage (in theory!)

[Floatingshed]

I have some film footage which has different picture geometry on alternate fields!

It is 25fps and when filtered thus: Assumetff().Separatefields()
plays as you would expect, updated picture information every other field, but the opposite field has slightly warped geometry.

On normal playback this looks like a stange combination of flicker, blurring and interlacing artifacts!

I really need to remove the strange fields and replace them with duplicates of the others. I am not sure how to proceed....

Any pointers appreciated. Thanks.

[johnmeyer]

You have to post a short, unedited, sample. The solution, if one exists, depends entirely on the exact nature of what is wrong.

[Floatingshed]

OK. The "original" is a .vob I don't usually edit these. What should I use to slice a few seconds off for you to view?
Also is there space on Doom9 to upload a clip or do I have to stick it on mediafire or some such?
Thanks.

[johnmeyer]

ffmpeg can be used. Womble lets you download a free trial (I think). Mediafire is a good place to upload.

[Reel.Deel]

OK. The "original" is a .vob I don't usually edit these. What should I use to slice a few seconds off for you to view?

Use DGindex (part of DGMPGDec (http://rationalqm.us/dgmpgdec/dgmpgdec.html)), load .vob, select start and end [], file save project and demux video. Another good tool is MKVToolnix.

[Music Fan]

Or TSmuxer.

[papcom]

OK. The "original" is a .vob I don't usually edit these.
Thanks.
Sounds for me as the filmtransfer was made in 16.6666 fps to PAL, or some blended 18fps Transfer put in a 25fps timeline, or whatever else people do, when they transfer films and put in on a 25fps Video DVD.

[Floatingshed]

Here is a slice of film!
It is very short but a static scene where the fault should be very apparent.
Thanks.

https://www.mediafire.com/?czaz2ctdmazgzb8

[johnmeyer]

When looking at the clip field-by-field, I can see the warping. Unfortunately, I can't tell much more because, I'm sorry to say, you couldn't have provided a worse test clip: you really need to provide something that contains movement.

[Floatingshed]

Huh? It's the warping that is the problem, its far less apparent in a clip with movement.
Why should there be warping between fields of a progressive clip?

[johnmeyer]

Huh? It's the warping that is the problem, its far less apparent in a clip with movement.
Why should there be warping between fields of a progressive clip?One possibility:

1. It started out, obviously, as film. Film is progressive.

2. It was telecined in order to show 24 fps on 29.97 NTSC television, or on 25 fps PAL television. Once telecined, it is interlaced video.

3. This interlaced version was re-sized without first doing IVTC. This can result in pretty nasty artifacts, including warpage, like your clip.

Again, this is just one possibility. The fact that it is warped rather than simply shifted (up/down or left/right) seems to point to a re-sizing issue.

One obvious "solution" is to bob it, get rid of the offending field, and live with the half-resolution version.

Hopefully smarter minds will offer better alternatives ...

[ajk]

I tried using Quad() (http://forum.doom9.org/showthread.php?t=165978) to get the fields to line up. But even when you get the border areas of the frame lined up, the middle part still trembles (or the other way around). So you'd need to split the image into more sections for better alignment. The warping does seem pretty stable if you just look at the odd or even fields, so it's probably doable, but very tedious using AviSynth. Need something with a GUI to figure out the distortion pattern.

Though frankly, the image is quite soft to begin with, so doing what johnmeyer suggests and discarding one of the fields and then resizing the remaining one back to full resolution works just fine and is very easy.


Source(...)

SeparateFields()
SelectEven()
BicubicResize(width(), 2 * height())

Stab() # If you want to stabilise the image a bit