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#1 Mikael Lemercier

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Posted 05 December 2005 - 05:06 AM

hi,
i looking for some advices for shooting with a F900 in a studio with a green back ground...
thanks
Mikael
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#2 David Mullen ASC

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Posted 05 December 2005 - 11:12 AM

Well, for one thing, you shouldn't do too much other than light the screen well (evenly), make sure it is pure green (kino greenscreen tubes are useful), get rid of spill on the subject, underexpose the screen a little (at least a stop), etc.

In terms of the camera, it's actually better to turn some functions off -- turn off edge enhancement (Detail), turn off Color Matrix, turn off ITU-709, etc. In other words, don't overly process the signal to try and improve the chroma of the screen, etc. because then you create edge artifacts that can make keying harder. Just light and shoot the screen well (correctly).

Talk to whoever is doing your composites as well and see what they want.
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#3 Mikael Lemercier

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Posted 18 February 2006 - 04:38 AM

Thanks you David for this wise answer.
what do you think about the shutter speed? can it make keying easier with a 1/200 speed for example?
regards.
Mikael.
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#4 Phil Rhodes

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Posted 18 February 2006 - 07:29 AM

Hi,

Short shutter periods can make it easier to achieve a "good" key. However, it really depends what you mean by good, as what you'll then have is an effects shot with a 1/200 shutter cut into a sequence with 1/48 shutter, immediately flagging it up as subtly different. For this reason I'm not a fan of the technique.

Phil
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#5 David Mullen ASC

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Posted 18 February 2006 - 11:32 AM

Yes, even though you'd get less blurry edges, making the keying easier, the choppier motion from using a shortened shutter angle isn't really worth it. You should be able to get a good key with a normal 1/48th shutter.

The bigger issue is the fact that the F900 records 8-bit 3:1:1 with a lot of compression, so there is sometimes some problem with slight chatter on the edges of keys. But there is not much you can do about that unless you budget for a better camera with a separate recorder.
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#6 Eric Steelberg ASC

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Posted 18 February 2006 - 12:09 PM

I have a FX client I shoot for regularly with the F900 on greenscreen. To get around the issues David mentions above, we set up the camera and digitize live via HDSDI straight to a PowerMac G5 with an HD capture card at 8 Bit, 4:2:2, uncompressed. The results are terrific and far superior than from what the camera records to tape.

It is also imprtant to have the screen underexposed from your shooting stop...with green I go 1 1/3 under, blue I go 1 1/2 under. Make sure the screen is lit as evenly as possible.

If there is a little color spill on your talent I wouldn't worry. The green spill will just be replaced with the color of whatever you replace the screen with and look quite natural.
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