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Old March 10th, 2007, 08:16 PM   #1
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Chromakey vs Vegas 7

Hi everyone! here's my question ;

I'm experimenting with chromakey in Vegas 7, i filmed my subject on a greenscreen (see pictures) i used the Chroma Keyer effect in vegas and adjusted these settings :
-low threshold = 0.600
-high threshold = 0.740
-blur amount = 0.010
I know they depend on the lighting used in the filming, but i still get a light greenish glow around the subject, if you look carefully at the pictures you will notice it (look at her hair and side of her arms) is there a way to correct this?

Thanks in advance!
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Old March 11th, 2007, 07:31 AM   #2
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u need to suppress the spill.. try running chroma blur before your keyer..
if it still spills, try running a sharpness filter PRIOR to the chroma blur... then run your keyer..
Shrapness will assist in differentiating contract levels prior to blurring..

also, make sure that your chromakey is confirgured using the "show mask" only tab checked..
check it and youll get a BW image..
in HERE is where u adjsut your levels.
theres no point telling us what your levels are at, as what might be acceptable to you, might be acceptabel to me.. and these images dont do much to help us work out the solution for you.

Is seems however that the talent might be too close to teh screen, hence the reflection/spill of green lightAnpoother thing that seems to be an issue is your lighting.. try to run a keylight on your subbbbbject and maybe a hair light above to "pull" your talenet away from the screen.. the lighting at this time looks to be throwing a shadow of your talent across the screen
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Old March 11th, 2007, 01:27 PM   #3
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Agreeing with Peter's post suggestions.

The best way to deal with green spill is not to shoot it in the first place. As P suggests, moving the talent away from the screen helps, and, lowering light intensity on the screen, increasing backlight, gelling backlight with straw or with minusgreen.

Generally speaking, good green screen work requires lighting the subject and the screen independently.
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Old March 11th, 2007, 05:25 PM   #4
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Thanks guys for giving me all this info, i will try it a.s.a.p.

What if i want to film a baby crawling on a greenscreen? i can't light the two subjects independently... have any suggestions?
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Old March 11th, 2007, 08:30 PM   #5
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of course you can :)
i regualrly let my boy don his superman cape and fly around the world.. he loves it..

trick is to just run a keylight on the moving subject (ie, have the light follow the talent) OR run a wider keylight for the area in which the talent is moving, THEN to light the background independantly.. maybe with somethign like a towel tota light with a brella to diffuse

this is where 3 point lighitng can make a huge difference and if u look it up here on this forum or anywhere, you'll find TONNES of info to help :)
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Old March 12th, 2007, 01:24 AM   #6
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It's not always easy to get the subject far away from the green screen, as you will need a larger room and a larger green back drop. You could therefore try a magenta filter (or minus green) as a backlight to the subject. Having said that, you are also up against DV (assuming you are filming in DV) which due to compression will give problems at the edges (chroma filter should be used, as already mentioned).

What vegas lacks is a decent spill suppresion filter, but you could try using the color correction filters to reduce the green spill. My preference is to use a separate package designed specifically for keying / compositing, which would have all the tools to give you maximum control over the keying process.
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Old March 12th, 2007, 01:28 AM   #7
 
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Add a ChromaBlur filter before the Chromakey filter, set to 2.00 horizontal only. That'll clean up some of the spill as well, and give you a smoother overall image.
Declan is right, spill suppression is non-existant in Vegas, but you can use the Secondary Color correction tool as a rudimentary spill suppression. Or, use a garbage matte, that always helps a LOT with this sort of problem.
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