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Green Screening... need advice!

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Paul Levin
Green Screening... need advice!
on Jun 16, 2010 at 10:30:15 pm

Hey all,

I'm editing a project where most the shots are done against a green screen. Being related to the martial arts, many of the shots have fast movements. As a result, I'm getting alot of webbed fingers, and hands/feet getting cut off on quick movements.

I have very little experience with green screens,and the little I've done was just talking heads. Now we're looking to shoot part 2, and I'm looking for suggestions on how I can eliminate this preferably in the shoot, otherwise in post. Would it help to shoot high speed?

We shot in DVCppro HD 720, but are open to other formats if it would help.
For post, I'm doing my keying in AE using keylight.

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Kevin Reiner
Re: Green Screening... need advice!
on Jun 16, 2010 at 11:26:26 pm

Every greenscreen key is a little different, so there is no one answer, but I'll throw a couple tips your way.

1. sometimes adding a "levels" effect prior to keylight helps. You'll have to play with it and even go into the separate RGB channels and adjust. You're trying to even out the green and make it true green, use the info tab to monitor.

2. When you choose the screen color you want to key out, place the eyedropper in a green area nearest the area you are having difficulty with. So if a hand is getting cut off, try selecting the green that is near that hand.

3. Move your cursor to a frame that has the worst key and change view to "screen matte". Now adjust the settings for "screen gain", "screen balance" and then in Screen Matte play with "Clip Black" and "Clip White". You're trying to get the image to be pure black and white with no noise of either. Then switch back to Final Result. Screen shrink and softness work together. Sometimes going -1 on screen shrink and then 1 on softness works well. Also, try changing the replace method from soft color to hard color.

4. You also might try using the AE matte choker in tandem with Keylight. You will probably have to dial back keylight and then use matte choker to clean the edge.

It involves a lot of trial and error, so it's hard to help you out without seeing the footage. Just keep tweeking it. I don't have any advice on how to shoot it as I just do the keying.

Good luck,

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Declan Smith
Re: Green Screening... need advice!
on Jun 17, 2010 at 5:55:35 am

When you shoot your part 2, increase the shutter speed in camera. This will help avoid the motion blur you are seeing. It\'s best to do some experimental shots to get the right setting if at all possible.

Declan Smith
FCS3 / After Effects CS5 / Combustion / Canon 7D / Canon XL2

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Kevin Knutson
Re: Green Screening... need advice!
on Jun 17, 2010 at 6:07:50 pm

Keylight is a tricky, but great keyer. Refresh your memory with their documentation. It is meant to handle motion blur, and indeed it can.

It kind of bothers me that Screen Gain is the top slider, as this is something you should try to avoid boosting. By doing so, you're probaly going to key out all your semi-transparencies.

Do be afraid to retry your key from the beginning several times, sampling different colors, using different slider values.

Change your bias colors to skin tones too.

But definitely revist the documentation as it will explain very clearly how to handle the key.

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Paul Levin
Re: Green Screening... need advice!
on Jun 17, 2010 at 6:42:36 pm

Thanks for all the advice! very helpful.

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