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Green Screen keying problems

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Tyler Joynt
Green Screen keying problems
on Jan 26, 2011 at 4:11:39 pm

We shoot on Panasonic HPX-500 cameras, but a couple of our producers love the "SPARK" scene file mode, which basically just blows the footage out so they dont have to touch it in post. It's helpful when they're in a rush, but it usually adds bad halo'ing, etc.

We recently shot a bunchhh of green screen footage at 720p60 DVCProHD, and SPARK was accidentally on purpose left on.
The halo'ing is just insane.

I'm using Keylight to key all the footage, and the only real thing i've found to do is Shrink the screen matte and soften it. It looks decent, and thankfully will be in an SD final output.

I was just wondering if there is a better method to keying out with problems like this. I even tried a trial of Nuke and Primatte, but it wasn't any better at all.

Any help would be great.

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Dave LaRonde
Re: Green Screen keying problems
on Jan 26, 2011 at 4:20:41 pm

Ouch. Remember that old phrase, "Garbage In - Garbage Out"? I'm afraid you're a victim.

Since chroma keying is all about the edges, and your edges have been compromised, your options are very few. I can only think of three: try the Matte Choker or Simple Choker in AE, live with the bad keys you have, or reshoot with proper camera settings.

Perhaps someone else can think of ways to salvage the footage, but it sounds like you've already pursued all the logical options.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

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Olin Padilla
Re: Green Screen keying problems
on Jan 26, 2011 at 8:26:31 pm

I think we've all been in this situation, and it sucks.

I can't see your footage, so I can't say anything too specific, but here are a few tricks I've been able to use in the past. These really depend on the footage, and it will only correct the look of the edge, not the precision.

1) Layer, layer, layer your keys. If you're lucky you might be able to hone in on that halo. (Not the Keylight effect itself, but the actually layers). Use mattes too.

2) Try to correct the halo with a light wrap. While you're at it, look into the Key Correct plug-in set from Trapcode.

3) If acceptable, try color correcting the composite background to match your ugly edges a little better.

4) In a few occasions, I've been able to salvage keys by doing this: Duplicate the layer after keying. Choke and feather the top layer. On the bottom layer, play with your blend modes. If the halo is light, you might be able to blend it with Multiply, if it's dark try screen. Fine tune.

Let me know if anything works. If you send a still, I can tell you more.

Also, if you have CS5 you might be able to use some of the decontamination tools that come with the rotobrush. Decontamination works the same way light wraps do, but it uses the composite background instead of a color. I don't have CS5, so I can't say how to do it.

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