Thread: Green Screen & Coloured Lighting

Can we ask what might be a daft question?
We want to buy some coloured lighting for our next video shoot.
We use a green screen which will obviously be lit separately & we will keep the colours away from the green screen.
But (before we part with any money) if we light the foreground & the talent with strong colour will this affect the way the camcorder sees the green screen behind it & make the chromakeying difficult?
Or can the effects of coloured lighting be simulated realistically in Sony Vegas after filming so we dont have to buy anything?
We'd really appreciate any advice on this.


Sarah & Allison

Sensible question.

If you have your camera on AWB (Auto White Balance) then strong coloured lighting in the forground can affect how it white balances which could affect the green-screen.

If you use one of the pre-set white balances or make sure that the AWB is switched off then it shouldn't be a problem. There are ways of giving a coloured lighting effect in post but it never looks as good or as sparkly as the original.

The colour of shadows can depend on the colour of the light.
I suspect that if the light creates green shadows, those might interfere with the keying.

Originally Posted by TimAndrews

The colour of shadows can depend on the colour of the light.

Not strictly true in that shadows are, by definition, where the light doesn't fall. The shadow's colour will depend on the colour of the ambient light. The only way you'll get green shadows is if you have a green light somewhere, which is obviously something to avoid when doing "green-screen" chromakey.

I concur, unwise to use a green gel. But, I assume green shadows could be produced from mixtures of other coloured lights.
It is a while since I have played with coloured filters and I know very little about lighting. Is it easy to identify gels or bulbs without any green?

White light (including tungsten) has a whole spectrum of light, including green but the chromakey software is looking for "green only" without the addition of red, yellow, blue, etc etc.

Unlike paint, whereby a mixture of blue and yellow produces green, adding blue and yellow light produces white and it is actually quite difficult to produce a decent green from a mixture of lights. If you had spectral yellow and cyan light sources you might get a green tinge where they overlapped but I doubt that it would be enough to cause any chromakey problems.
This is one of the reasons why the three additive primaries are Red, Blue and Green because these are very difficult, in some case impossible, to create from a mixture of other colours.

For fun, if you get a light with a magenta gel and shine it onto an object, the shadow will sometimes look green. It isn't green, it's an optical illusion but people can get quite convinced that they're seeing a colour which just isn't there.

Originally Posted by The Gaffer

For fun, if you get a light with a magenta gel and shine it onto an object, the shadow will sometimes look green. It isn't green, it's an optical illusion but people can get quite convinced that they're seeing a colour which just isn't there.

I've a feeling that I actually would find that fun. Is this an indicatio I really should get out more

Originally Posted by TimStannard

I've a feeling that I actually would find that fun.

Fun.

The best optical illusion I have seen all year Richard Wiseman's Blog

Many thanks for all the replies/discussion/opinions.
We're looking at buying some par cans with coloured gels.
We film in a room only 12 feet wide, & felt to light the talent & avoid spillage onto the green screen we should buy the par 56 spots rather than the floodlight type.
Is this the right thing to do?


Sarah & Allison

Originally Posted by TimAndrews

Fun.

The best optical illusion I have seen all year Richard Wiseman's Blog

Streuth!