Another Green Screen Question

mattharding · September 9, 2004

I know this question must have been asked before, but I searched the archives and could not find it. Maybe I'm doing something wrong.

When shooting chroma key/green screen strictly for transfer to video, what is the best exposure for the screen on a reflective reading (so that a digital artist can pull a good/clean key)? I figure about one stop hotter than 18% grey? So let's say that I set my key such that I want to expose at an f4, I want to light the green screen so that the reflective meter tells me f5.6--right?

David Mullen ASC · September 9, 2004

No, I'd expose it at the same reflective reading as the key, not hotter. If anything, the subject (if Caucasian) should be a little hotter than the green background in terms of IRE levels.

Markus Rave · September 10, 2004

I try to stay about half a stop below key with green and bluescreen shootig video. That adds to the color saturation and gives good results in post.

Markus

oscar jimenez · September 10, 2004

Ok, lets say:

Reflected reading: green screen at background reads t 4.0. subject " caucasian women " her light read with gray card for key light is t 4.0 and her skin reads 5.6. Then shall be exposure be set at t 4.0 ?. Ive known a theory that says, green or blue set a zone V, skin tones for good rendering + be higher one zone from V or green screen. Opinions on this?

David Mullen ASC · September 10, 2004

Sounds about right, a caucasian face is one zone brighter than the background screen.

When shooting HD, I expose the greenscreen at least one stop under what would get me a zebra pattern at 70 IRE.

Nitin Sagar · September 12, 2004

while shooting movement over chroma screen..will shutter angle help in terms of a crisper key?

oscar jimenez · September 13, 2004

I dont know but I think "moderate shutter" might help. IN video I always ad a 1/100 to 1/125th of shutter max. I have tried with shutter over these ones but they only give me problems.

Michael Nash · September 13, 2004

A faster shutterspeed will help minimize motion blur, which could give you a slightly sharper edge for matting any single frame. But you'd just end up with motion that looks unnaturally strobed, which wouldn't help your key look any more realistic or better. I would shoot the foreground pass with the shutterspeed you desire for the final comp.

Phil Rhodes · September 13, 2004

Hi,

I'll second Mr. Nash's comments. If your keyer can't even deal with motion blur, it's going to have a hell of a time with genuinely tricky stuff like hair. Or rather, if removing motion blur helps it look better, there's already something wrong.

Phil