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Old July 13th, 2004, 01:10 PM   #1
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Lighting for Chroma Keys (blue or green)

Hi all,
I edit for a show that uses a combination of live actors in a studio and a virtual character that is used in it's own virtual setting. The character is also used in the live studio where it interacts with the human actor (and vice-versa). We have a fully equipped studio that is painted in chroma blue. While the lighting grid is impressive looking, the lighting person has no clue (or so it seems) about how to light for keying. When editing on the Avid MC, I'm having a bitch of a time with shadow areas and blue spill on the actors skin and clothing.

I've talked to them already about backlighting but it's still very challenging to key out.

Do you guys have any advice about how to light properly? I use the standard tools in Avid to key out, maybe I need a better plug-in?

We also have a hardware Ultimatte system that seems to be just collecting dust. But to use it, the producers would have to plan all our shots way in advance (and backgrounds) and these people don't have the time it seems.

Any advice appreciated.

Robert
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Old July 14th, 2004, 12:12 PM   #2
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Yeah, they don't have time to plan it out and get it right, but you have
time to fix the impossible on their deadline . . . right? Errrrrrrrrrr.

Anyway, having all the gear without smooth lighting doesn't
help much, but from the sounds of things, tell your lighting guy
to buy either a bunch of soft boxes or a ton of flourescents to flat
light the back wall. Use side lights on the actors to keep the shadows
off the back wall (unless you want those shadows) and again some
soft light for front fill on the actors to smooth out what the side lights
can't cover. Back light the actors with Lee 103 gel.

If the back wall is lighted smooth to the camera's eye and the actors
are looking good without too much spill,
your results should be better and much quicker to achieve.

Get that ulitmatte box out and play with it or send it my way ;)
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Old July 15th, 2004, 03:07 PM   #3
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You will find a lot of good tips at the Ultimatte website. Also, check out Kino Flo: http://www.kinoflo.com/product/b_g_screen/bluegreenscreen.html

You can use that Ultimatte keyer for test purposes to see if you have the ability to pull a good key.

It is very difficult to tell by eye if your blue screen is evenly lit. A waveform monitor would be a big help here. A few people I know used to shoot black and white Polaroids to help them tell if the screen was even.

One of the most common problems is positioning talent too close to the background, where they pick-up colored bounce from the background.

Wayne Orr, SOC
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Old July 15th, 2004, 03:46 PM   #4
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If yr cam has "Zebra, use this feature to optimize backlight uniformity.
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Old July 15th, 2004, 09:46 PM   #5
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Thanks guys for your responses, I will print them out and pass along to the lighting director.

I have fired up the Ultimatte box today and using one playback deck as foreground, the other deck as the BG...was able to get a really clean key on most shots. The only problem areas were when the talent was lieing on the floor (blue). Massive shadows and blue spill on her arms/legs. Still, with a bit of tweaking, I got pretty good results.

I've heard about an Ultimatte plugin for Avid. Anyone use that? Any good? I've been getting mediocre results with default keyers in media composer.

Thanks again,
Robert
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Old July 16th, 2004, 09:21 AM   #6
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I don't have that plug in on my avid, but I've been on the avid L for years.
The built in Avid keyer is about as bad as they come, and I've
heard lots of positive comments about the ultimatte plug in.

What format are you shooting on? DV doesn't make the best keys,
but there are some tricks that can help. Lighting is still the biggest
factor in making it work (at all).
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Old July 16th, 2004, 07:03 PM   #7
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"The built in Avid keyer is about as bad as they come, and I've
heard lots of positive comments about the ultimatte plug in."

OK, good, I thought maybe it was me :=) I've tried the keyer within the 3D Warp effect and it sometimes does a better job. However, hardware Ultimatte rocks!

We shoot on DBeta and BetaSX. Actually, I'm surprised that for such a large company, lighting techs don't seem to be trained properly for lighting for blue/green screen. Funny, cuz there is never a shortage of guys who will put on a fresh coat of paint on the set.

Regards,
Robert

One director once suggested to shoot against black and use luma keying. DUH!
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