EX1 mystery flicker - Sample clip link attached.

S

stulanka

Member
This video is only two seconds long and I'd like you to just take a look and if you can shed some light on what the problem is - then you're a genius, thanks :)


Recently my camera has a tendency to flicker, for just one frame as I'm shooting and I've noticed it in the edit. It's like it's readjusting itself for just one single frame.

You can see it in the above video, but it's very quick. You almost don't notice it and most clients won't do, but some will and I need to get to the bottom of it, as I'm shooting some much more technically demanding footage very soon.

The picture goes fractionally darker and greener in the top left - it's also visible in the black of the man's shirt, but not so visible in YouTube...

Any clues?

Thanks

Stu
 
Are you using fluorescent lights? I had a similar problem when I used fluorescent lights. It depends on the frequency of your lights and the frame rate you are filming on. Here I film in 25p and my electric supply is 50hertz, so my lights don't cause a flicker. if you use a ballast with fluorescent lights then that will fix the problem as well. I think the problem comes in when I tried to film 24p here in South Africa where the power is 50Hertz.
 
sadude said:
Are you using fluorescent lights? I had a similar problem when I used fluorescent lights. It depends on the frequency of your lights and the frame rate you are filming on. Here I film in 25p and my electric supply is 50hertz, so my lights don't cause a flicker. if you use a ballast with fluorescent lights then that will fix the problem as well. I think the problem comes in when I tried to film 24p here in South Africa where the power is 50Hertz.
Click to expand...

I think this kitchen had halogen spots. I had the same problem before in natural light with halogen spots. The natural light was in a big corporate greenhouse where the clouds kept adjusting the light. In all case though I was filming in 25p and at 60HZ I think. Perhaps I'll try 50HZ next time and see if that makes a difference. I couldn't work out whether it had something to do with the shutter...

Thanks for your advice.
 
I saw it after about 3-4 plays, and it's something I've seen on the FS100.

I'm not really an expert in image processing or video compression, but I can spot a story - even if it's invented. Could this be the Long-GOP image processing software churning away until it reaches the end of its parameters in subtle changing circumstances, and then doing a deft re-tweak to 'change gear' so to speak?

I saw this in JVC cameras, and of course it was demonstrated in the 'split screen' situation where one could witness how two identical image processing circuits could go down two separate paths of recording the image, generating a difference in gamma and highlight compression. This only came to light because the HD100 used two separate processors on one image, half and half.

I fear that your EX1's processor was following one strategy in image tone compression until it ran out of wriggle room and snapped to a different strategy - note the skin tones are accurate all the way through, it just does something to the non-skin tones. That's what I'd want - if there's skin tone in the picture, do everything to preserve that because we look at people more than we look at backgrounds.

How do you cure it? Difficult, as the process is over in 2-3 frames. How do you avoid it? I think you hit a very rare harmonic.
 
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