Blue AND Green?

[CalmReason]

Stupid question (perhaps) and first post, so please forgive my ignorance.
Is it possible to have BOTH a blue and green screen.
I want to shoot a surreal bedroom scene with the bed linen blue and wall green. Not sure why, yet, perhaps a night sky on the wall and the sea on the linen.
If it is possible, what software would you recommend a) with a budget and b) Open Source/hobbiest/free?

[CalmReason]

OK - in doing research, I may not have enough space between the actors and the screen to not cast a shadow.
And I did find a thread showing that it can be done.
Is there such a thing as a back-lit screen?

[david walsh]

Many people make a wrong assumption when they hear backlight in relation to green/blue screen. A backlight shines on the back of the subject from above the screen.

There's no reason why with the right material you couldn't light a screen from behind, but it kind of defeats the purpose as it would require a lot more space, and it's not going to work with bed linen. If you imagine a screen lit from behind being like a big lamp shade, it would still cast light over your subject.

The way to reduce spill is by getting the right amount of light on the screen, it's not a massive amount that's necessary, it's the even spread that's important. To light a screen from behind you'd also need more light than from the front to penetrate the material, but it's always worth experimenting with to see what you get. The key (puns are good) to understandng green/blue screen is experimentation, guided being best.

An old and still used technique eliminates the keying aspect altogether and is known as rear projection, you projet a reversed image/video onto a screen from behind, this shows through the screen and the camera records the subject and the background live. Again, it needs much more room.

You can do blue and green screen in the same video, but you then get more hastles when dressing sets/subjects. Often the same colour for both screens is fine, but that aslo depends, especially if they over lap. Which, including if they even get close, causes even more problems with green light spilling onto the blue screen and vice versa.

Have you looked into chromatte, sadly it's very expensive, and it wouldn't let you do both green and blue at the same time.



David.

[CalmReason]

This sounds great - but I don't think I have enough space (or budget).
The 'set' is a bedroom with the actors leaning against the wall. I was wondering if I could 'Green' the wall and just for fun (art) 'Blue' the bed.
I don't have pro lighting either.
I vaguely wondered if I could move the bed and have a kind of stiff green screen with a green light behind, but I think I'll still run out of space (as its a real bedroom and not a studio :-(
Thanks for the help