Foreground exposure and skin tones

[Nathaly Pinheiro]

Helloo,

I understand that the lighting in foreground should be as similar as posible to what the replaced image will be, considering color, direction and angles of light but does it also apply the intensity of lights/exposure? For example, if the final image will be dark,  should I expose a white actor around 70IRE and darken it in post? Or around 40IRE ? 

A teacher once said that the subject should never be exposed at the same level as the green screen, and the green screen should always be exposed for medium gray for better latitude. So, what if the actor has brown skin? 

[David Mullen ASC]

It's a tricky question. The green screen generally should be exposed fully to medium grey-ish level no matter what unless there is a special reason.

But if the subject is supposed to be dark in the final composite, the question is how much to underexpose them. I tend to split the difference and just darken them a little but not as much as I'd like, then talk to the compositor about the look. It's complicated because I've still had some composites come back with the subject too bright and had to get it redone.  But I'm nervous about having a subject too underexposed.

[Nathaly Pinheiro]

Thanks David. Could you explain why would an underxpose subject be a problem in a green screen when you want them to look underxpose in the final image? If the edges are sharp and with a good backlight to help separate them form the green screen, wouldn´t that be enough? And the chroma well lit of course

[David Mullen ASC]

Shouldn't be a problem in theory unless the bright screen is causing some flare around, or spill onto, the subject. The trouble when a subject is dark is that they sometimes pick up more green spill on them. But there is spill suppression software these days.

Really comes down to what the vfx supervisor and compositor want to work with.