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Colored pre-exposure?


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#1 Chris Keth

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Posted 15 August 2005 - 10:39 PM

Has anyone ever pre-exposed film (flashed) with color rather than white? I'd love to see the look it yields if anyone knows of some footage that did this. If it works like I expect, it should tint the shadows that color and have little to no effect on mid tones and highlights. It might be a neat effect after some testing.
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#2 Dominic Case

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Posted 17 August 2005 - 12:41 AM

You are right about how it should work. I can't point you to any examples of this, but I played about with the techniques some years ago. The pre-exposing, or flashing, colour has most effect on the shadows as you say, but tends to put a bit of an overall cast on the whole image, though leaving highlights more or less neutral. It's quite interesting to do this and then grade the result in the opposite direction, so that the shadows are returned to neutral and you get the opposite colour cast in the lighter tones.

You tend to reduce overall contrast as well - after all what you are doing is the same as flashing, though affecting some colours more than others.

The difficult thing is predicting how much effect the colour will have (and therefore what exposure to give the pre-flash). It tends to affect every scene differently.
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#3 David Mullen ASC

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Posted 17 August 2005 - 08:37 PM

The Lightflex (originally Colorflex) invented by Gerry Turpin was designed for this purpose, to flash the image through the lens with colored light (although white light can be used.) The Arri Varicon replaced the Lightflex.

Turpin got the idea while looking out through a window with a green curtain on one side, and seeing the view through the reflection of the green material on the glass.

He built a prototype for the movie "Young Winston". The Lightflex was also used heavily on "The Wiz" (Ozzie Morris) and "Dune" (Freddie Francis).

The trouble is that since it affects the blacks and shadows more than the highlights, the amount of contrast in the final print or transfer to video will affect how much you can see the effect.

I've tested colored flashing using gels on the Panaflasher, but the effect was pretty subtle since I kept the flashing low.
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#4 John Pytlak RIP

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Posted 18 August 2005 - 07:21 AM

Kodak's Wendy Discher once presented a technical paper at the SMPTE that discussed techniques in photographic modification of tone and color reproduction. Generally, flashing the camera negative or duplicate negative film will affect the shadow areas (e.g., a red light flash will add red to the shadow areas). Flashing the master positive or print film will affect the highlights (e.g., a blue light flash will produce yellow highlights).

As noted, flashing generally REDUCES contrast. The level of flashing (e.g., as measured by the density above "D-Min" the flash produces) and the exposure or "curve placement" of the scene information determines how much the flashing will affect the image.
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