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Green Screen Halo

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Tony Ingrassia
Green Screen Halo
on Jun 12, 2008 at 3:06:10 pm

I've got an issue with some chromakey work we're doing. We're shooting with a JVC GY-HD250 at 720p 59.94, which is being captured directly into Final Cut using an AJA Kona3 card. For our set, we're using two Kino Flo Diva Lite 400's to light the green background, and two ARRI 300's to light the subject (also a 650 bounced off the ceiling for some backlight).

The problem is that we're getting this very small white halo around the subject when shoot. It appears on the raw footage, so it's not a problem with the keying software (Conduit). You can see what I'm talking about here:

http://www.activatedmarketing.com/halo/halo.png

http://www.activatedmarketing.com/halo/halocu.png

Any ideas on what could be causing this, and more importantly, how to fix it? It's either got to be something in the way the camera is interpreting the signal, or the way we're lighting the set.

As a side note, any opinions/experience as to whether it would be better (for keying) to shoot using 1080i instead of 720p? With the 1080i you're getting a bigger picture, but would the interlacing have a negative effect on the key?


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john sharaf
Re: Green Screen Halo
on Jun 12, 2008 at 3:09:09 pm

Tony,

Probably "detail" setting in camera is too high, creating artificial edge. Either turn down or off and try again!

JS





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Rick Amundson
Re: Green Screen Halo
on Jun 12, 2008 at 3:32:04 pm

I agree that it is a "detailing" issue. I'm not familiar with the settings in the JVC but you should look at the overall detail setting, maybe the vertical detail setting or vertical detail frequency but lowering your overall detail should solve the problem.

Rick Amundson
Producer/Director/DP
Screenscape Studios
Bravo Romeo Entertainment
http://www.screenscapestudios.com
http://www.bravoromeo.com
http://www.indeliblemovie.com


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jon agnew
Re: Green Screen Halo
on Jun 12, 2008 at 5:49:56 pm

Agreed....detail issue. Encountered the same thing with a Canon XH-A1.



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Rick Wise
Re: Green Screen Halo
on Jun 12, 2008 at 6:32:17 pm

If you zoom in on the larger shot, you can see that the white edge is least visible around light objects (her hair) and most visible around dark objects (her dress, and also her arms which are less brightly lit than her face.) Video has a hard time going from dark to light, cleanly. I suspect the posts about detail are correct. However, as you dial down detail, you may begin to have trouble getting a clean key on her hair.

Try: dialing down detail; putting her in a lighter dress; brighten her arms a bit; and, use 1080i. Ideally you'd try one at a time to see if the change helps.

Rick Wise
director of photography
Oakland, CA
http://www.RickWiseDP.com
email: Rick@RickWiseDP.com


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