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Blue-Screen backgrounds in Adobe CS5 "too" dark...????


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#1 Fred Magilicutti

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Posted 27 January 2011 - 09:46 AM

I have an interesting thing that is happening when blue-screen compositing in Adobe CS5, and I'd like to know your opinions on it. The source video for the foreground subject and background scene are both coming from the same HD digital video camera.



As some shooters have instructed previously, when the blue-screen behind the subject is "under exposed" by 1 to 1-1/2 stops, it is supposed to achieve the best results, and the compositing does go fairly well. But, when the background is put in behind the "properly created" subject matte, the background is "dark" by about 1-2 stops.



If I "over expose" the blue screen, the background ends up correctly exposed behind the subject.



Trying to alter the brightness of the background does not do it.



So, now you can see the dilemma I am in: A well exposed blue-screen produces a good matte but a dark background, while an over exposed blue screen produces a properly exposed background, but a lousy matte.



What to do......?????
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#2 Adrian Sierkowski

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Posted 27 January 2011 - 11:37 AM

Have you tried:

1) exposing at key? no under/over.
2) thought of going to a green screen
3) what CS5 program are you using? I get best results with keylight 1.2 in After effects; which allows you to play with the screen gain ect.

Also you don't mention what "HD" camera you are using, or how you are posting the footage.
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#3 Scott Fritzshall

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Posted 27 January 2011 - 05:13 PM

So that I'm understanding you properly: Are you saying that the subject exposure stays the same, and the background plate exposure stays the same, and the only only difference is the exposure of the blue screen? Does the background plate actually change brightness depending on the foreground plate you're using?
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#4 Adrian Sierkowski

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Posted 28 January 2011 - 11:58 AM

No, I'm talking about when you shoot the scene, have you tried, one your camera, exposing the blue screen at the same level as the talent.
Also, I can't answer #2 without knowing how you're keying. I know in After Effects if I don't get a "good" key on a green screen I'll wind up with a "black overlay" from keylight dimming down a BG plate until I adjust the screen gain.
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#5 Scott Fritzshall

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Posted 28 January 2011 - 01:23 PM

Oops, sorry Adrian, I was addressing Fred, not you. I was asking those things because from the way it's described, it sounds like it could easily be a compositing error.
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#6 Adrian Sierkowski

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Posted 28 January 2011 - 02:57 PM

Quite alright Scott, was just confused and figured I might as well clarify ;)
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#7 Ian Blewitt

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Posted 10 February 2011 - 02:23 PM

Take a look at your Matte and see if the background is grey instead of black. It seems like it is not keying everything out.
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