green screen problems

Z

zoob

Active member
1) I've just noticed a darker green horizontal bar slowly moving up my green screen shooting AVCHD footage. What is it and what can I do about it?

2) I set the white balance but now I see it's a darker shot than leaving it set on auto. I'm starting to think perhaps this is related to problem 1.

Editing with newblueFX chroma key in Vegas Pro 10c.

Thanks
 
It's probably a hum bar. First thing is to verify it's actually been recorded, so does it reverse when you reverse play on the timeline? If it does, then you have as trickier snag.cause wise, it's the video version of an audio ground loop. When you shot it, the ground for the camera, or audio devices or other electrical kit produced small voltages that linked to your camera via attached cabling. The ground loop interference is locked to the mains frequency, while your camera used an exact frame rate, the small difference produces the moving bar.

Is it bad enough to impact on they keying? Can you widen the colour/saturation/level acceptance to let it key properly. The keyer in premiere is forgiving enough to be ok as long as your subject hasn't got too much green spill on the edges. I occasionally get this problem, and the cure is to ensure everything is powered from the same building supply. If you use whatever outlets are around the space, there's no guarantee they're on the same supply, and just a tiny amount of current flowing in the ground connections can make a mess. Often it's very subtle and unless you really look, you don't see it. A solid background is the worst for these things to remain hidden.
 
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