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Color Gels that can literally boost film's chroma?


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#1 Jonathan Bowerbank

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Posted 08 March 2007 - 06:47 PM

So, John Carlson at Monaco here in San Francisco, challenged me for my class project to see if I can find a type of gel that can actually increase or boost the level of chroma on a film's emulsion.

I generally know that with film, what's inherent in its chemistry and physiology is what you get...but has anyone ever seen an increase in chroma in their projects solely from a certain type of lighting, with gels or at a different exposure?

My project is basically to explore film's limits when under and over exposing to find out at what point certain colors are no longer salvageable...but he just threw this challenge into the pot to see if I'd explore it further.

Any suggestions?
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#2 Frank Barrera

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Posted 08 March 2007 - 09:14 PM

So, John Carlson at Monaco here in San Francisco, challenged me for my class project to see if I can find a type of gel that can actually increase or boost the level of chroma on a film's emulsion.

I generally know that with film, what's inherent in its chemistry and physiology is what you get...but has anyone ever seen an increase in chroma in their projects solely from a certain type of lighting, with gels or at a different exposure?

My project is basically to explore film's limits when under and over exposing to find out at what point certain colors are no longer salvageable...but he just threw this challenge into the pot to see if I'd explore it further.

Any suggestions?

Sounds like a trick question as chrominance refers to a video signal and has no relation to film exposure.
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#3 Jonathan Bowerbank

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Posted 08 March 2007 - 09:48 PM

Sounds like a trick question as chrominance refers to a video signal and has no relation to film exposure.


Would you prefer the word "color" ;)
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#4 Michael Nash

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Posted 09 March 2007 - 02:04 AM

Well since it's your class project, I won't outright give you an answer. But I'll give you a one-word hint: density
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#5 Satsuki Murashige

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Posted 09 March 2007 - 03:44 AM

Hey Jonathan,

I'm a little confused about what you're trying to accomplish in your test -- it sounds to me like you're trying to find a way of increasing the color saturation of the film stock beyond what it can normally produce by using a gel or by under/overexposure. Is that about right?

It seems to me that getting a highly color-saturated image on film is most successful when you have highly color-saturated objects to photograph (regardless of whether they are painted, dyed, or lit by color gels). I think any boost in color that you get from re-rating your filmstock will be so slight that a few tweaks of the knob in the telecine suite will completely obscure the difference between a normal negative and a moderately dense negative.

Of course, you could start by shooting with a highly color-saturated reversal stock like Fuji Velvia 50D which you can get at Spectra Film and Video in LA (expensive, though!), and pola and grad filters would help. In fact, if you're open to using filters, you could try shooting tri-color process (multiple successive exposures on the same film stock with pure red, green, and blue filters) to emulate a 3-strip Technicolor look. Combining that with a highly color-saturated subject in front of the camera ought to give you what you asked for.

So: Velvia reversal stock + tri-color process + highly saturated subject = B)

Some links about Tri-Color:
http://en.wikipedia....rokudin-Gorskii
http://www.adorama.c...;article=032105

The Spectra link:
http://www.spectrafi...o.com/Film.html

P.S. How do you like John's class so far?
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#6 Jonathan Bowerbank

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Posted 09 March 2007 - 12:41 PM

It's not really part of my project, just something that Carlson threw out there when I was describing what I wanted to do. But yeah, you basically got it right. But I figured, only if I could find something "special" to do with the stock, then I'd try and follow through with it. The tri-color process sounds like an interesting thing to explore.

I already considered polarizers and such, and it's true, they do make those colors really pop, but it's more by elimination than addition.

Thanks guys for your recommendations, I'm just gonna stick with my original idear, but figured I'd open it up to any suggestions.

:)


btw, the class is pretty cool, we'll be movin' on to more hands-on stuff soon, I can't wait!

Edited by Jonathan Bowerbank, 09 March 2007 - 12:42 PM.

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#7 Michael Palm

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Posted 09 March 2007 - 02:49 PM

btw, the class is pretty cool, we'll be movin' on to more hands-on stuff soon, I can't wait!


What school and class is this for?
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#8 Michael Nash

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Posted 09 March 2007 - 06:09 PM

:rolleyes: Okay, here goes -- what is an image on a negative? It's colored dye clouds. The "thicker" or more dense these clouds are, the more saturated the image appears. Think of it like a stained-glass window -- the thicker the glass used, the more "dense" and color-saturated the image appears (using colored glass, not painted). It's the same image, just "more of it."

So how do you control density? By the development of the dye clouds through exposure to light and chemicals. If you want extra density you overexpose or overdevelop (push process).

Exposure to "white" light affects all the color layers of the film equally, controlling overall density (therefore saturation). Exposure to colored light (through gelled lighting or a colored filter on the lens) exposes the layers unevenly, giving you extra density in the exposed color and lowered density in the complement (relative to a "normal" exposure).

But then you'd have an image that's balanced overall toward the colored gel or filter you used. So what if you wanted to control saturation of some colors but not others, AND have a normally color-balanced image? Using only film & lab techniques, nothing digital -- what would you do? I'll give you a clue; it's still all about density. ;)
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#9 Phil Rhodes

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Posted 09 March 2007 - 07:50 PM

Hi,

It's an aside, and not the answer to your question because it only works in very specific circumstances, but there were (are?) filters for an internal filter slot in the F900 (possibly the Panavision version) which have a three-peaked transmission curve, one in each of the red, green and blue. They were designed to produce purer colour for bluescreen shots, but they're effectively a high-saturation filter. Presumably this could be made to work for film, but it was reliant on being able to clamp this highly specialised filter in a very precise position.

Probably you could look this up and mention it for extra credit, or something.

Phil
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#10 Glenn Hanns

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Posted 09 March 2007 - 07:56 PM

So, John Carlson at Monaco here in San Francisco, challenged me for my class project to see if I can find a type of gel that can actually increase or boost the level of chroma on a film's emulsion.

I generally know that with film, what's inherent in its chemistry and physiology is what you get...but has anyone ever seen an increase in chroma in their projects solely from a certain type of lighting, with gels or at a different exposure?

My project is basically to explore film's limits when under and over exposing to find out at what point certain colors are no longer salvageable...but he just threw this challenge into the pot to see if I'd explore it further.

Any suggestions?


Try looking at the Rosco range of calcolor filters, although they affect only one spectral band by reducing transmittion of the other chroma values.
From blurb:

Calibrated color, by Rosco is a series of color effects lighting filters designed specifically to the spectral sensitivity of color film. The series includes the primary colors Blue, Green and Red, along with the secondary colors Yellow, Magenta and Cyan followed by Pink and Lavender. Each color is designed in four densities: 15, 30, 60 and 90, corresponding to the familiar ½, 1, 2 and 3 stop calibrations.

In color photography, three light-sensitive emulsion layers separately record the individual blue, green and red components of the spectrum. CalColor filters adjust the transmission of these color components at the individual light source in a familiar and reliable manner. As a result, the cinematographer can exercise selective and predictable control over the image's coloration as rendered by the film.

Glenn Hanns
Cinematographer. ;)
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#11 Jonathan Bowerbank

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Posted 09 March 2007 - 09:18 PM

Try looking at the Rosco range of calcolor filters, although they affect only one spectral band by reducing transmittion of the other chroma values.


Those are the gels I had already planned on using :)

I'd like to use the 90 density, I've used 60 in all colors and didn't find their color intense enough.

Thanks all for your input, they will all be taken into account and I'll let you guys know the results of the tests and possibly post them in a quality format online.
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#12 Michael Nash

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Posted 09 March 2007 - 10:03 PM

Those are the gels I had already planned on using :)

I'd like to use the 90 density, I've used 60 in all colors and didn't find their color intense enough.

Thanks all for your input, they will all be taken into account and I'll let you guys know the results of the tests and possibly post them in a quality format online.


So what are you trying to do exactly? Increase overall color saturation, or just certain colors? And are you aiming for a neutral color balance?
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#13 Jonathan Bowerbank

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Posted 09 March 2007 - 10:12 PM

through underexposing and overexposing each color in separate shots, I'm not only trying to play around with film's color saturation...but ultimately, I'd like to test the limits of the stock (7217) to see at what point is the color no longer salvageable using a push or pull process (subjectively, when do I start hating the color's image)

Also, I'm going to shoot the same scene, using some familiar everyday colorful objects (fruits, etc.) under plain white tungsten, then with daylight balanced lighting and another setup where they're lit using a full CTO on my lights to see if I notice any color loss in those objects upon color correction and whether or not they could all be intercut.
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#14 Michael Nash

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Posted 09 March 2007 - 10:43 PM

through underexposing and overexposing each color in separate shots, I'm not only trying to play around with film's color saturation...but ultimately, I'd like to test the limits of the stock (7217) to see at what point is the color no longer salvageable using a push or pull process (subjectively, when do I start hating the color's image)

Also, I'm going to shoot the same scene, using some familiar everyday colorful objects (fruits, etc.) under plain white tungsten, then with daylight balanced lighting and another setup where they're lit using a full CTO on my lights to see if I notice any color loss in those objects upon color correction and whether or not they could all be intercut.



Sounds like a good test. Let us know what you come up with.

You might be interested in these articles:

http://www.cameragui...ting_limits.htm

http://www.cameragui...candlelight.htm
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#15 Satsuki Murashige

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Posted 10 March 2007 - 03:19 AM

What school and class is this for?

City College of San Francisco. The class is called Film 90 Advanced Film and Digital Finishing. It's taught at Monaco Labs in SF by colorist and company VP John Carlson. It's once a week, 4 hour class. It's a really good class and cheap too :)

Here's the blurb about it from the school's catalog:
FILM 90. Advanced Film and Digital Finishing (3 units)
Lec-3, lab-3, field trips
Prereq.: FILM 24, 25 and 56; and completion of or concurrent enrollment in FILM 54
Repeat: max. 9 units
Advanced survey of state of the art practices and technologies in celluloid and digital film finishing and laboratory work, including timing, color correction, film to tape transfer and tape to film transfer, taught through lectures, field trips, and hands-on exercises. Class meets primarily off campus at a local laboratory facility.

http://www.ccsf.edu/...og/homeHR.shtml
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#16 Daniel Madsen

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Posted 11 March 2007 - 09:54 PM

[quote]what's inherent in its chemistry and physiology is what you[quote]what's inherent in its chemistry and physiology is what you get...but has anyone ever seen an increase in chroma in their projects solely from a certain type of lighting, with gels or at a different exposure?[/quote]

A confusion of terms I think. But assuming I understand you correctly, I would have to answer yes.

Color saturation affects the density of the negative, which affects the color saturation of the positive. The only thing that gels do is affect color saturation. A red gel in front of tungsten light illuminating a red surface, when exposed, will boost the density/color saturation on film more than if you used no red gel. This is the same reason for lighting a green screen with a green light.

Edited by Danielle Frankinshten, 11 March 2007 - 09:57 PM.

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#17 Kim Sargenius

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Posted 25 March 2007 - 06:54 PM

Thanks guys for your recommendations, I'm just gonna stick with my original idear, but figured I'd open it up to any suggestions.



Have you tried didymium / enhancers?

http://en.wikipedia.org/wiki/Didymium

http://www.singh-ray...olorintens.html

I've only ever played around with them (Tiffen ones) and there does seem to be some increase in saturation - especially in the warmer colours.

Most of the available ones are designed for on-lens use but I wonder if they might work on lights as well? Some of the sizes should fit on a Dedo...


cheers,

Kim
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#18 Dominic Case

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Posted 26 March 2007 - 02:26 AM

OK, since Kim Sargenius has mentioned them, I know John Carlson won't mind if we provide a little more discussion about color enhancing filters (or rare earth filters). I'm sure that's what he sent you out to look for.

Many colours in nature reflect a wide range of colour wavelengths. It's the proportion of each that results in the colour. However, as we know, both our eyes and film emulsions reduce the complete spectral profile of a surface to three values: the effect on the red, green and blue receptors (cones) in the eye, or on red-sensitive, gree-sensitive and blue-sensitive emulsions in film.

Because the sensitivities of each layer overlap considerably, almost all coloured objects result in a response in all three layers, and invariably a considerable response in two of them. What colour enhancing filters have is a narrow band of filtration in the overlap areas. So the elements of colour that hit more than one emulsion layer (or cone in the eye) are filtered, while the pure primaries get through relatively unattenuated. (It's a slight effect, but enough to make a visible difference). Through such a filter, therefore, reds appear much more saturated, as do greens and blues (particularly, I find, artificial paints etc: look at a row of cars through one of these filters!). There is no overall bias towards any colour, just an increase in saturation (or, using the video-related term that Jonathan used quite clearly, chroma.)

I have some sunglasses with a layer of this stuff, and Ira Tiffen was good enough to explain to me how they work, over on another list. I think I have it more or less right.

Please say Hi to John for me, Jonathan.
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#19 Kim Sargenius

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Posted 28 March 2007 - 07:47 PM

OK, since Kim Sargenius has mentioned them, I know John Carlson won't mind if we provide a little more discussion about color enhancing filters (or rare earth filters). I'm sure that's what he sent you out to look for.



Dominic,

Thanks for putting that so much better than I could! And with an explanation in words that I can actually understand!


cheers,

Kim
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#20 Phil Rhodes

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Posted 28 March 2007 - 08:20 PM

Course if that's really what you want, you could always light the scene with RGB clusters of LEDs, which will give you narrow spikes in each colour record.

Hmm, that's interesting. I wonder if one could increase apparent saturation in that way.

Phil
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