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Mysterious white shadows under arms of keyed subject

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dan caz
Mysterious white shadows under arms of keyed subject
on May 24, 2012 at 8:00:40 pm

I am having this problem in both Premiere using Ultra Key and AE using keylight. Almost everytime I key out a subject and clean everything up as best I can there is this white matter that appears between the arms and body. The closer the arm is to the body the white joins between the two. I don't know how to get rid of it. Is this a lighting issue?

Here is a link to some screen shots
4200_whitematter.jpg.zip

Thanks

Daniel Caza


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Dave LaRonde
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 1:23:46 am

It could be a lighting issue, or it could be a footage issue. From your description of the problem, we would need a crystal ball to tell.

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


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John Cuevas
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 12:11:33 pm

You posted the result, how about a still of the problematic green screen shot.

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.


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dan caz
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 2:52:14 pm

Here is a green screen shot. It's not perfectly lit but with a garbage matte the differing shades aren't a much of a problem. I am shooting with a sony hdr-sr11, a handycam basically but it shoots hd.

Image here:
4203_greenscreen.jpg.zip

Thanks

Dan Caz


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Dave LaRonde
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 3:58:28 pm

The lighting on the green screen isn't awful, which is good. However, the thing that's really hurting you is the Handicam footage.

Not all HD is created equal. The digital encoding & decoding algorithms they use, called codecs, toss out a TON of color information to make the file size smaller. A handicam image almost always has 1/4 of the original color information. It's still enough to fool the human eye, but not a computer, and it becomes most apparent at the edges of the subject. And what do need for a nice, clean color key? Nice, clean edges, and a handicam isn't capable of doing it.

Once recorded, the damage is done: there isn't a way to reinvent the missing color information. The best you can do is to use one of the chokers in AE to get rid of the problem edges. You may have to use animated garbage masks to apply the choker to the problem area alone.

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


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John Cuevas
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 5:05:23 pm

Dave's probably correct about the cause of the white. For giggles I tried to key your shot. I turned off "unpremultply result"(big improvement) checkbox, changed the screen gain to 89, screen balance to 51. In the Screen Matte settings I went with clip black to 41 and clip white to 80. Finally I chocked the shot using the Screen Shrink/Grow to -1.0

Here's the result(some white left, but not as bad):

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.


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dan caz
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 5:17:41 pm

Thanks for the help John

I wouldn't have thought to uncheck that box because every tutorial I've ever seen on the subject either ignores it or says to keep it checked.

I'll give those settings a try. Appreciate it!

Dan Caz


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dan caz
Re: Mysterious white shadows under arms of keyed subject
on May 25, 2012 at 5:14:45 pm

Thanks Dave

You're absolutely right - the edges are the worst! The key looks much too smooth and fake by the time I've choked the life out of the edges just to clean them up.

I am really starting to understand the disadvantages of handycam "HD". It looks fine to just play back but takes a major quality hit when editing. Now that I think of it, bad edges are my biggest problem every time I do green screen, now I know why. Gotta save up I guess.

Thanks again!

Dan Caz


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