Sudden (and very inconvenient) luma change -- why?

[mg262]

One of my AVISynth filters is being (substantially) messed about by a sudden luma change in a clip I am working with. It really puzzles me because it's happening in the middle of a scene where nothing else happens and I haven't observed this kind of sudden luma variation anywhere else in the episode.

The source was field shifted, and I corrected that in this 7-frame sample:
HuffYUV AVI (http://people.pwf.cam.ac.uk/mg262/posts/sudden%20luma%20change.avi)

But if you prefer to look at the original, it's here (circa frame 56):
Source MPEG (field shifted) (http://people.pwf.cam.ac.uk/mg262/posts/sudden%20luma%20change.m2v)

You can also see from that MPEG that the luma is otherwise extremely stable.

For what it's worth, this is from a DVD of an episodic French cartoon from the 80s.

I would really love to know why this is happening; once I have a source model I will hopefully be able to do something about it... any illumination on this issue would be very much appreciated.

[hartford]

I've seen this in my analog captures of anime.

I don't know why it happens.

I've seen other "artifacts" with older anime; "hard coded" stuff (bad interlace
at 3, 6, and 12 frames).

I deal with it as best I am able.

[Mug Funky]

it's possibly a splice, if it didn't happen before in the cartoon. does the audio click at all in the same place?

btw, for a DVD there's some real timebase problems in that :)

other than a splice i really have no idea why that would happen. copied Macrovision tapes will do that, but every 4 seconds or so, all through the movie, so it's not that. also those flashes tend to be top-to-bottom.

[mg262]

Thanks for the thoughts, guys. Audio doesn't click... but it's pretty quiet at that point so that's probably it. (I take back what I said about the luma being 'extremely' stable by the way... if I jump back and forward 100 frames, there are places where it changes slightly. It's all a bit of a pain to analyse because it's so noisy.) The weirdest part was where I was searching for a sudden luma change and found someone's hair changed colour halfway through a scene for no reason!

for a DVD there's some real timebase problems in thatYup, that single-handedly shelved my plans for background superresolution in Cel (i.e. reconstructing a background of high-resolution than any of the individual frames). I did rig up a script/filter that alleviated the effect a fair bit, but it wasn't terribly effective so I put it away. (It will be much easier to fix once the background is probably reconstructed.)

http://people.pwf.cam.ac.uk/mg262/posts/tbc%20attempt.png
(you probably need to look at that at 2x)

[Mug Funky]

The weirdest part was where I was searching for a sudden luma change and found someone's hair changed colour halfway through a scene for no reason!

one of the animators probably finished off a pot of paint and got a new one. old one might have got dirty, but it doesn't seem likely (i'd imagine studios being pretty strict about contamination).

...unless you mean the hair changed from blonde to brown...?

[mg262]

http://people.pwf.cam.ac.uk/mg262/posts/Sebastien%20colour.png (http://people.pwf.cam.ac.uk/mg262/posts/Sebastien%20colour.png)

The whole foreground cel seems to change somewhat. It's not a problem at all, just a bit freaky.