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using B&W stock for chroma-keying?


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#1 Niki Mundo

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Posted 16 October 2007 - 04:00 PM

Can I do that? With like a brilliant white screen or something?

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#2 Michael Nash

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Posted 16 October 2007 - 07:26 PM

You can pull a luminance key from a black and white image. A "chroma" key needs color.
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#3 David Mullen ASC

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Posted 16 October 2007 - 07:33 PM

Luminence keys aren't good for subjects with light areas; even for a b&w film, it would be better to use color film and do a chroma key, make the composite, and then convert to b&w.
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#4 Niki Mundo

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Posted 16 October 2007 - 08:14 PM

I excepted more from you guys. I thought someone was gonna post "yes, it's being done all the time".
I'm disappointed at the lack of leadership around here. Someone should step up to the plate.
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#5 David Mullen ASC

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Posted 16 October 2007 - 08:48 PM

I excepted more from you guys. I thought someone was gonna post "yes, it's being done all the time".
I'm disappointed at the lack of leadership around here. Someone should step up to the plate.


There is a whole history of attempting to do keys in b&w -- the Williams Process, the Dunning Process, etc. Most old b&w movies avoided the problem by using rear projection instead. These luminence keying processes (like the Williams Process, used for some mattes in "King Kong") had problems with glowing edges, etc.

And the Dunning Process (also used in "King Kong") was practically a form of chroma keying:

<a href="http://en.wikipedia.org/wiki/Dunning_proce...Dunning_Process" target="_blank">http://en.wikipedia.org/wiki/Dunning_proce...Dunning_Process</a>

The Dunning Process

Various improvements and extensions of the process followed, the most famous being Carroll D. Dunning's, an early method built on the bipacking technique and used for creating travelling mattes. It is described thus:

The foreground action is lighted with yellow light only in front of a uniform, strongly lighted blue backing. Panchromatic negative film is used in the camera as the rear component of a bipack in which the front film is a positive yellow dye image of the background scene. This yellow dye image is exposed on the negative by the blue light from the backing areas, but the yellow light from the foreground passes through it and records an image of the foreground at the same time.

The Dunning Process, often in shorthand referred to as "process," was used in many black and white, most notably King Kong. Its chief limitation was that it could not be used for colour photography, and the process died out with the increasing move toward production of films in colour.

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Douglas Trumbull's company did a type of luminence keying for their composite effects like in "Star Trek: The Motion Picture" and "Blade Runner", shooting a color pass against black and then a silhouette pass against white (or taping the model with white tape and shooting it against black) and making hi-con b&w hold-out mattes from this pass -- but this required motion control for moving models or cameras and didn't work for non-repeatable movement in live-action photography, since it required multiple passes.
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#6 Daniel Sheehy

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Posted 17 October 2007 - 12:30 AM

I excepted more from you guys. I thought someone was gonna post "yes, it's being done all the time".
I'm disappointed at the lack of leadership around here. Someone should step up to the plate.

They did answer you, pretty clearly mate.

No, you cannot do a 'chroma' key using B&W stock. You can do other things.. not a chroma key though.
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#7 David Sweetman

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Posted 29 November 2007 - 03:03 AM

Why?
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#8 David Mullen ASC

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Posted 29 November 2007 - 03:14 AM

Why?


Now I can't tell who is joking anymore.

Because chroma = color. A green or blue screen behind an actor on b&w film is just a grey background. You could make it a white background and pull a luminence key.
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#9 David Sweetman

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Posted 29 November 2007 - 01:40 PM

Now I can't tell who is joking anymore.

Because chroma = color. A green or blue screen behind an actor on b&w film is just a grey background. You could make it a white background and pull a luminence key.

Sorry I meant to ask "why" regarding the original proposition: Nikki's insistence on using b&w stock to achieve a b&w final comp. So I meant, Nikki, why not go the easier and better route; is there perhaps some reason why you can't? Or don't want to? I probably should have made it more clear than a single-word post, but I was overcome by "what the hell???" factor, which, I'm coming to think, was the only real intent from the start. Probably if he was actually making a b/w film he woulda thrown that info in there.
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Visual Products

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