how to remove light 'flickering' (or pulsating)

Baluardo

Baluardo

Well-known member
Hello,

i'm trying to remove some annoying effect i got in a few shots where i get pulsating bright areas. it is shot in a forest and caves and the bits of sky which are visible through the branches 'pulsate' (it's like detail changes up and down each frame). it's actually the whole detail of the background area which pulsates. this effect happens also on premiere when i edit, not just on tv.

i posted the sample in vcd resolution (it's visible even with that) at
http://www.baluardoproductions.com/pulse.mpg

it was shot in default PAL 'cine' setting (i think with thin detail). also, it looks like depends on the focusing distance since i have one shot with the character coming towards the camera and when he's far the problem doesn't exist and when he gets close the sky starts pulsating. camera was on a tripod, exposure locked, 'auto' focus.

i tried blur, antialias, broadcast colors, and a lot of other filters. nothing.
i wouldnt say the shots are unusable, but not too nice looking for a technical eye.

suggestions?
would have that be different shooting with 'thick' detail?

thanks everybody!
Andrea
 
I don't see the pulse till after he picks up the flame and moves toward the camera??
Did it go away after he left the frame with the flame??
Maybe the iris is fluctuating with the flickering of the flame??
 
> I don't see the pulse till after he picks up the flame and moves toward the camera??

exactly that makes it even more weird.
Anyway i realized i have another take where he doesnt' get as close to the camera and there's no flicker at all. but the framing is much nicer in the one i wanna use :)

> Did it go away after he left the frame with the flame??

the take ends after 2 sec and the flicker is still on

> Maybe the iris is fluctuating with the flickering of the flame??

i doubt it since i have other shots where the light (natural) is very steady and still happens. also if i scan it frame by frame with premiere i see that the it's the detail itself (of the whole screen!) pulsating from even to odd frames on and off...

Andrea
 
It seems to be related to the flicker of the torch. When he's further away, it has no effect as the torch is only a small proportion of the whole frame. As he gets closer the torch, and his shirt lit by the torch, dominate the frame and that's when the flicker starts.

It seems too rapid to be iris fluctuation, so might guess it's some sort of electronic gain fluttering. Are you sure you didn't have AGC on? There would be a little green letter "A" in a box at the top of your flip out LCD display.

Don't think it's really detail fluctuation as it doesn't affect the dark areas. That might also rule out AGC.

Noticing a lot of Mpeg artifacts, especially around the torch and his arm. It may have been caused by something in the AVI to Mpeg conversion. Is it there in the original footage off tape?
 
ericyoung said:
It seems to be related to the flicker of the torch. When he's further away, it has no effect as the torch is only a small proportion of the whole frame.
Click to expand...
Well i have another shot i didnt share with you guys where there's no torch, in the middle of the forest, with very stable light, and still i get the same prob.
so I think it's not torch related.

AGC was off. i was using a manual 6 dB gain though. but only in this shot, not in the forest shot.

Noticing a lot of Mpeg artifacts, especially around the torch and his arm. It may have been caused by something in the AVI to Mpeg conversion. Is it there in the original footage off tape?
Click to expand...
This footage i shared with you guys is mpeg1 VCD resolution, so obviously mppeg artifacts are significant. i didn't analyze in details the original footage, though.

nobody every experienced something like this?
since this happens at alternating frames, i am prone to think it depends on the frame-field and progressive related issues when image really thin and contrasted subjects (tree branches)..

anyway, if somebody has suggestions on how to fix it, that would be great!

Andrea
 
ok, for the patient ones (it's 35MB) the original avi dv footage is here:

http://www.baluardoproductions.com/pulse.avi

i dont notice anything very weird except the pulsating light.
with some attempts, i got modest improvements choosing 'interlace consecutive frames' right clicking on the timeline..

solutions still welcome:)

Andrea
 
What you get is the result of thermal turbulence in the in the zones where the torch passed (passes). It "moves" image area's and changes intensities due to changes in the diffraction index changes in the heated air.
 
Hi Andrea -
I wanted to say thanks for all your advice in answer to my questions about a month ago. I've posted our new video on dvxuser - its listed as "trailer for HAND GUNS."
Best,
Malayka
 
ballyhoo42 said:
I wanted to say thanks for all your advice in answer to my questions about a month ago. I've posted our new video on dvxuser - its listed as "trailer for HAND GUNS."
Click to expand...
no prob. happy that sharing my little knowledge was useful to you. i watched the videdo, it's intriguing!

if you happen to know how to fix my little prob here, you're welcome! :)
Andrea
 
Hi Andrea,
sorry I can't help out with your problem, I don't know a whole lot yet. Thanks for looking at my trailer.
Malayka
 
hey Baluardo,
If you did want to use that shot, you could frame by frame rotoscope it, wouldnt be that hard either if your familar with after effects.
 
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