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Transparencies and chroma key?


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#1 Alrike Claassen

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Posted 22 February 2010 - 10:41 AM

Hi everyone, I am new on this forum, so forgive me if this topic was covered recently.

We are doing a production where we deal with a lot of transparent and semi-transparent objects. Some of the problems we've encountered was with a plastic bottle filled with water. We also have some sequences coming up with rain and smoke.

How do you deal with this? Is it usually added in post with visual effects or is there some trick I can use in the studio to avoid this problem?
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#2 Kevin W Wilson

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Posted 22 February 2010 - 05:58 PM

The smoke and rain gags are done typically with a black background instead of green, although I've seen it done successfully with green too so you could use either. Black tends to provide a better key with natural elements like smoke, fog, rain, sand blasts, etc.

I would use a black backdrop for the smoke and rain and put a strong backlight on both elements. Rain can be completely invisible on camera without a good backlight, same goes for the smoke.

www.detonationfilms.com has an assortment of stock elements that may give you some ideas. Almost all of their rain and smoke footage is shot on black and keys pretty well.

Do the glasses with water in them have to be clear? Using an opaque glass would solve a lot of the transparency and warping issues of seeing the green through the glass. This happens a lot when interviews are done in front of green screens with people wearing glasses. Looking closely can reveal un-keyed parts of the screen through the lenses on the individuals glasses. The key can be difficult to pull around those areas without intensive rotoscoping or clean up, simply removing the glasses though can solve the problem.
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#3 Alrike Claassen

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Posted 23 February 2010 - 04:07 AM

The smoke and rain gags are done typically with a black background instead of green, although I've seen it done successfully with green too so you could use either. Black tends to provide a better key with natural elements like smoke, fog, rain, sand blasts, etc.

I would use a black backdrop for the smoke and rain and put a strong backlight on both elements. Rain can be completely invisible on camera without a good backlight, same goes for the smoke.

www.detonationfilms.com has an assortment of stock elements that may give you some ideas. Almost all of their rain and smoke footage is shot on black and keys pretty well.

Do the glasses with water in them have to be clear? Using an opaque glass would solve a lot of the transparency and warping issues of seeing the green through the glass. This happens a lot when interviews are done in front of green screens with people wearing glasses. Looking closely can reveal un-keyed parts of the screen through the lenses on the individuals glasses. The key can be difficult to pull around those areas without intensive rotoscoping or clean up, simply removing the glasses though can solve the problem.


Thank you Kevin, that helps a lot.
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rebotnix Technologies

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Rig Wheels Passport

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Broadcast Solutions Inc

Media Blackout - Custom Cables and AKS

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Metropolis Post

Aerial Filmworks

The Slider

Tai Audio

Visual Products

Paralinx LLC

Glidecam

New Pro Video - New and Used Equipment

Willys Widgets