Noise reduction smearing over scene-change - fix?

[Lyris]

Hey everyone, I have an old Betacam SP cassette that's going out to DVD. It's of a feature film.

The film was transferred in 1995/96 on some sort of CRT telecine device. Believe it or not, this master was made for the VHS release of the film, so we're very lucky that it's in its original aspect ratio. (The "fuzzy" letterboxing you see is actually in-camera mattes. It's going to be cropped very slightly to the intended 1.66:1 and go to Anamorphic DVD).

The source is very detailed, so no problems there, and a little bit of noise reduction (to get rid of 'gritty' analog video noise) and then re-graining (to keep the intended look) will help make it look as good as possible.

There is just one problem. The source appears to have some sort of "baked-in" noise reduction. That, or some sort of CRT image persistence (I think my first theory is more likely though). It's not too bad, but when there's a sharp scene-cut, details from the previous scene are blended into the next. This example is of the worst instance in the film - this is a 3 frame sequence.

Frame 1: ending of first scene

http://i51.photobucket.com/albums/f383/lyris1/Image3.jpg

Frame 2: first frame of second scene, with smear

http://i51.photobucket.com/albums/f383/lyris1/Image4.jpg

Frame 3: second frame of second scene, clear.

http://i51.photobucket.com/albums/f383/lyris1/Image5.jpg

So as you can see, the ending frame of the first scene is carried over to the first frame of the next scene, after this, the problem goes away.

My question is, can anyone share a technique for fixing this? Even if I have to do it by hand for each occurrence, that's OK. Perhaps there is some way to subtract the smear by referring to the previous and prior frames?

(BTW, those image grabs are direct from the tape with colour correction. I'm doing more work on it to bring it up to standard).

[AVIL]

My two pence:

If the source is interlaced, could be merged on deinterlacing two half frames of different scenes. Try to see the scene change in virtualdub after separating fields (with avisynth).

good luck

[Lyris]

It's essentially progressive (PAL 2:2 transfer). We only have whole frames to deal with, sadly.

[poisondeathray]

Why not replace #2 with a duplicate of #3 , and turn down the brightness a bit?

[Emulgator]

I found the same artifact in old PAL transfers.
Because I had to push up shadow saturation a bit on these it became obvious:
Seems like one of the first 3D Colour noise reductions going over 2 frames.
Only colour information of any given frame is delayed and mixed into the 2 following frames
with a factor of roughly 0.3 and maybe -0.1.
This is not only there at fades, it appears throughout the footage, but is best visible at hard cuts into black.
Most of the time I tried to force fades to go through black while adding keyframed desaturation for 4 frames before
and resaturation for 4 frames after the cut.
A "learning" avisynth script would do the best trick here
(finding the CrCb factors that have been applied to get a black frame back
at a known-to-be-black place).
Meaning filtering back, but maybe adding unwanted colour sharpness and colour noise back in.
poisondeathrays solution sounds good to me and I would add desaturation around cuts and deeper fades as a smoother here.

[Lyris]

It looks like in the mean time, I'll just have to find the most offensive occurrences and remove it by hand as suggested.

[Didée]

This might be a reasonable start...

http://forum.doom9.org/showthread.php?p=1140719#post1140719