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Chromakey Problems

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Andy Stinton
Chromakey Problems
on Sep 21, 2007 at 8:01:00 pm

I have some unevenly lit green screen that I am dealing with . First any tips on how to get around this issue ( he asks hopefully ) . The second issue is much more worrisome . I


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Floh
Re: Chromakey Problems
by
on Sep 21, 2007 at 8:15:03 pm

[Andy Stinton] "I have some unevenly lit green screen that I am dealing with . First any tips on how to get around this issue ( he asks hopefully ) . "

Light it more evenly ;-)
Seriously, there is no "easy" way around it. If you get badly lit footage the keying results will suffer. A relatively easy way to prevent that (although it is not really cheap) is to use e.g. the Reflecmedia setup (http://www.reflecmedia.com/). This is an LED ring and a special cloth, which gives you very good results due to the fact that the LED create a very even blue/green background without the need to use additional lighting. The only drawback is that you tend to get a slight "halo" around your foreground object.



[Andy Stinton] "All looks fine in the preview window but after rendering it I get flashes of light similar to a series of camera flashes going off .. Any ideas as to why this is happening?"

This shouldn


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Kieran Matthew
Re: Chromakey Problems
on Sep 21, 2007 at 10:34:19 pm

Hi Andy,

[Andy Stinton] "I have some unevenly lit green screen that I am dealing with . First any tips on how to get around this issue"

I had a similar tough time doing a simulated virtual studio sequence that had terrible lighting.

In RED you have several keyers with various options, and I found that each shot, and even each person/area within that shot needed to be treated separately rather than a "one size fits all" approach. Specifically experimenting with the setting that lets you choose HSL,Hue,RGB etc for colour matching.

I divided the screen into areas with different layers for each and used the crop settings to isolate them. Then I adjusted the settings for each to give the best results.

I also used masks painted with the vector paint tools and tracked with the motion tracker to both limit the key areas, and to "put back" clean areas that the key had disrupted.

For instance, the presenter had frizzy red hair that refused to key. She was split into several zones; her body used one set of keys, her head specifically used another colour match.

I could get her hair to key nicely at the expense of her face, and particularly the reflections in her eyes & teeth, so I painted a mask over her face and tracked it to her movements. The mask was applied to a layer of clean video resulting in a good key on the hair, but with an untouched face.

I also had trouble with things like the chairs and table legs (which were all chrome of course!) disappearing in the wide shots. For that I grabbed a still and used Photoshop to cut the legs etc out. This still was then overlayed in Boris to fix the problem.

Alternatively you can try a package like Shake or AE for the keying. I used Shake for another sequence as it managed to preserve the shadows on the floor that RED couldn't handle.

Anyway, hope some of that helps!

K




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