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Keying out fire and subjects. Green screen?
We are shooting a scene where we need to key out the background and replace it with a different set. Normally this would be an easy task (shoot it all on a green cyc, chroma key, etc.) but we also hope to have a practical fire gag in the shot (our star is getting set on fire).
We plan to shoot with a Sony F3 into a Samurai recorder (200mb/s), but also to shoot high speed on a FS700.
Has anyone ever keyed out fire on green before? Does it work well? I’d love some advice as we have never done something like this before.
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5 Replies
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If I were setting this up, I think I would shoot it over black, and then use an add mode to drop out the black, or maybe a luma key. Should be less issues with transparent issues of the fire tinting green then.
Johnny Cuevas, Editor
Thinkck.com“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb. -
We talked about that too, but its hard because of shadow and modeling on the subjects, black in clothes, etc. then all get removed as well. Hrm…
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I’d strongly suggest doing as many tests as possible before then. Try green & black. From experience, I can tell you that it’s much cheaper to test vs. not testing and learning after that it can’t be done in post.
Johnny Cuevas, Editor
Thinkck.com“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb. -
i would think that it would be somewhat difficult due to the way chroma keying typically works. Since fire is not totally opaque, there will be varying degrees of green throughout the fire. I would recommend using something like keylight, and even that may not give you the look you want. I would recommend compositing the fire in post instead of during the shot because it will turn out cleaner.
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If you have to do this practically I might try a blue screen instead of a green screen.
I’d expect most fire to be a blend of red and green values with very little blue. If you can find a substance that will burn very red then that might help the green screen.
In addition blue is darker than green which may help you out if you need to use an extra luma key on the fire in addition to the chroma key.
Finally, if you can do some simple tests yourself that should help you figure out any problems with the process.
Darby Edelen
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