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Problem with DFN filter... urgent !


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#1 Benjamin_Lussier

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Posted 26 June 2005 - 11:11 AM

Hi,

I'm visual effects supervisor on a commercial next week... Its a green-screen shot with an actor and a couple of props. Thing is ... the scene takes place at night. Its in a studio. The DP's this old guy who doesnt like to rely on digital color grading. And he was about to use DFN filters on a greenscreen shot!! I explained why he couldnt do that. Cuz we need the contrast between the bright green and the actor, so it also makes underexposing dangerous. Is there a compromise?

I mean we're bound to color grade the shot anyway... but still.

Here's a reference PIC I showed him... Its from Harry Potter 3, photographed by M. Seresin. Can you notice any kind of filter? Cuz I dont. Looks to me like its a "gel" job.

CHeerios

Ben

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#2 David Mullen ASC

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Posted 26 June 2005 - 11:58 AM

If you're the visual effects supervisor and the one who has to make the composites work, he should take your advice into account and understand the reasons why.

Is he trying to match an exterior scene shot with the DFN filter?
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#3 Benjamin_Lussier

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Posted 26 June 2005 - 12:06 PM

The background that will be "comped in" is actually a miniature that hasnt been shot yet. Should I allow him to use DFN filters and underexposure on the miniature shot ? And then try to match it in post ?
I feel like Ive seen too few winters when it comes to cinematography. Thank god for this forum.



Ben

Edited by Benny_the_kid, 26 June 2005 - 12:08 PM.

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#4 David Mullen ASC

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Posted 26 June 2005 - 12:14 PM

Well, if this is a "moonlit" scene it should be underexposed to some degree -- it's not accidental underexposure in the sense that you won't be later brightening the image in post, so noise & grain should not be an issue because the image will be left dark. Therefore it would be the correct exposure.

There is also the question of how you will match the non-efx photography in the scene.

But it's definitely safer to not overdo the underexposure for the composite elements and let you darken things in post.

If the DFN filter does funky unrepeatable things (i.e. you can't recreate the look in post without it) and you can't shoot both the background and foreground elements with it, then it might be safer to shoot without it, but you'd want to test that. Besides, you don't have to underexpose with the DFN filter as much as it is designed to do -- you could open up a little. On the other hand, with a miniature, you'd want to stop down more, so the ND component of the DFN filter might not be a good idea if it doesn't allow you to stop down. Normally with DFN photography, you want to shoot at a wide aperture because deep focus looks unrealistic at night, but in the case of a miniature, you want deep focus because it makes it look more in scale.
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#5 Stephen Williams

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Posted 26 June 2005 - 12:48 PM

Hi,

Here's a reference PIC I showed him... Its from Harry Potter 3, photographed by M. Seresin. Can you notice any kind of filter? Cuz I dont. Looks to me like its a "gel" job.

CHeerios

Ben

<{POST_SNAPBACK}>



Hi,

I did a DFN shot on green screen. I exposed 1 stop brighter than normal for a DFN so the green would only be 1 Stop Under. It worked better than the same scene shot without the filter and just underexposed. I would't risk it on blue as the blue would go very dark!

If your in a studio its easy, just over expose the background 2 stops and add the DFN filter.

Cheers,

Stephen
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#6 Phil Rhodes

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Posted 26 June 2005 - 02:40 PM

Hi,

It depends what the DFN filter is going to do to it, but however you choose to expose the foreground, it's usual to expose the background about half a stop under whatever the stop would usually be. You're then free to underexpose the foreground to your heart's content, but underexposing the screen would be a recipe for disaster.

Frankly I'd be extremely cautious about any kind of filtration beyond basic colour correction. A deep blue DFN filter on a green screen would cause it to be massively underexposed. It is the compositor's responsibility to be something of a colourist anyway, for exactly these kinds of reasons.

Phil
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#7 Benjamin_Lussier

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Posted 26 June 2005 - 03:24 PM

yeah.. thanks for your help guys....
.. Im off..lol... testing phase for me til next thursday

Thanks you very much indeed

Ben
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#8 Stephen Williams

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Posted 26 June 2005 - 03:57 PM

it's usual to expose the background about half a stop under whatever the stop would usually be.

<{POST_SNAPBACK}>



Phil,

I usually expose the background at Key. I have tested under exposing but noticed an increase in grain. I know you seem to favor green screen over blue screen. From many tests on 35mm and DigiBeta I don't find any overall advantage with green over blue. Last week I tested smoke and water and both keyed very well using an Ultimatte based keyer.

Stephen Williams DP

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#9 Benjamin_Lussier

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Posted 26 June 2005 - 05:33 PM

The actor's hair's brown, its easier to key with green than blue.
Blonde hair is definitely better with blue though.
Plus, the DP will probably use blue gels on the lights.. I dont need blue spill in front of blue background.
Green is also cheaper to light properly.... you also get less spilling with green...so .. In general I prefer green... :)

Cheerios

Ben
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#10 Phil Rhodes

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Posted 26 June 2005 - 06:29 PM

Hi,

The only stuff I've ever done has been green, part from a few trivial examples, so I can't and don't reccommend either way - although I have seen comparative tests on NTSC DV and the green was vastly better.

Phil
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#11 Stephen Williams

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Posted 27 June 2005 - 01:52 AM

The actor's hair's brown, its easier to key with green than blue.
Blonde hair is definitely better with blue though.
Plus, the DP will probably use blue gels on the lights.. I dont need blue spill in front of blue background.
Green is also cheaper to light properly.... you also get less spilling with green...so .. In general I prefer green...  :)

Cheerios

Ben

<{POST_SNAPBACK}>


Ben,

Whilst I agree with blond hair blue is safer. I am more interested in what is the colour of the final composite! I don't want green reflections in a scene that's mainly blue!

Stephen
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#12 Benjamin_Lussier

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Posted 27 June 2005 - 03:54 PM

Im more worried about the blue gels in the lighting set up than the green spill and reflections from the background... which are easy to get rid of.

Cheerios

Ben
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