Help Me out: Greenscreening at night

[Jackson Miller]

Hey guys. I need to have an effect like Andrew Kramer's car hit (link), except that I need to do it at night. Is this even realistic to try or should I be considering another method altogether right now? I am assuming that if I just went out and did it like andrew did, except at night, the screen would be unevenly lit, dark, and de-saturated because of the dark. And obviously de-saturated green is not a good chroma color. So here are a few things I have considered:

1) Shoot the whole darn thing day for night.

- Pros: Don't have to worry about lighting, and will be able to get a perfect key/matte.
- Cons, may not match well with the shots directly before and after it, which WILL be shot at night.

2) Shoot the two elements separately: the car going by at night, and then the actor in front of the greenscreen at the same location but in the daytime with as close to the same framing I can get. Then, I can key out the actor, and adjust just that keyed out footage to make it look like the actor was outdoors at night (essentially day for night but only on one small part of the shot, the actor).

-Pros: The shot would have actually been at night and match the rest of the footage for the most part, while still having the benefits of daytime lighting for the actual greenscreen part.

-Cons: Seems a bit more complicated and more ways to possibly mess up. Actor may seem fake, and even more separate from the actual scene when the whole point is to make him look like he belongs in that shot and was actually a part of it.

3) Do the whole thing at night and try to light the greenscreen from behind so that it glows a bit and I can get a good outline of my character.

- Pros: Might work

- Cons: May cast weird green shadows. May cause character to be silhouetted which is not what I am going for. I would have to light him from in front to compensate, but we are trying not to draw too much attention as it is and use no lighting for this shot, since it would be very hard to get legal permission to do this in the middle of a street in Pasadena (or a look alike).

4) Use an alternate method, AKA no greenscreen. Any suggestions?

Pros: Easier

Cons: Not as convincing, cool, or professional looking.


Right now I am leaning towards shooting a whole bunch of footage so that I can try it all of the ways listed and have options when edit time rolls around.

 

[Jackson Miller]

One more thing: I will be using a GH-1 as my primary camera for this film. Does anyone know how well it holds up to color keying stuff like this?

 

[kwoff]

Not sure if this would work or not, but you could try shooting it at night on location against a black screen, lighting only the actor (or if the background is dark enough, ditching the screen altogether). You would then key out the black or use a luma key to get rid of the background, which could work, assuming you are able to minimize spill on to the screen or background. The benefit would be that you would not have to light the background, so there wouldn't be any effect on your foreground lighting, and you could use the same lighting setup you use to shoot the car.

Good luck,
Kevin

 

[craigbowman]

Greenscreen is done using layered light. The idea is the lighting of the screen is completely separate from the lighting of the objects and people placed well out in front of the screen.

You light the objects and people according to the requirements to best match the shot of what will eventually be keyed into the area occupied by your greenscreen.

Without even a basic understanding of how these processes work don't beat yourself up over the results. Invest in the dvd series vfx for directors from the folks at hollywoodcamerawork and you'll be well down the path on how to handle everything.

 

[kwoff]

I thought Entity's question was not how to do green screen generally, but how to do it at night, since the reflection from a well lit green screen could be difficult to separate from the foreground elements when shooting in low light. If I misunderstood, sorry to have provided an unresponsive answer.

Kevin

 

[clang]

Greenscreening is so dependent on good lighting that I strongly suspect trying to shoot it at night just won't work, you'll either get a worthless key and/or spill green light all over your foreground objects. By all means try a quick experiment though.

I suggest also quickly trying the day for night method - if the whole film (or at least all the shots on the road where the car stunt is set) is shot that way and your 'night' post-production filters work ok, that may be the best option. But if only some of the film can be shot during the day, I'd expect nightmares making the day-for-night shots match the real night shots. You missed one pro of shooting day for night - it can be a lot easier shooting during the day, although that does depend a lot on weather, lighting, location avaialbility etc.

I've seen car hit stunts done without greenscreening, simply using masking and blurring - so long as the impact is very fast and you don't need to see blood and carnage during the hit, it can be done pretty quick and nasty as it will only occupy maybe a half a second of screen time.

 

[Jackson Miller]

Thanks for the replies guys. And yes, I know how to greenscreen (though I am by no means a pro obviously) and have done it several times with successful results, but always in a studio type setting with very controlled lighting.

I suppose I will have to do some tests. Shooting the rest of the scenes day for night is out of the question for a couple reasons, but also, I will be using the GH1 for this and I really would like to take advantage of its beautiful low light performance. I am more of a cinematographer/director than a special effects man, but that's why I came here. Right now I am leaning towards doing something like number two. I'll have to try it out in a bit. Any other suggestions would be greatly appreciated.