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Can Film Actually Capture the Color Violet


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#1 Peter Ellner

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Posted 03 June 2011 - 12:30 PM

From what I know about color film, there are only three layers capturing cyan, magenta, and yellow light, which means corresponding to red, green and blue. But violet is actually a spectral color of a shorter wavelength than blue, so how is violet light captured on film? Is it impossible?

I know that digital cameras can fake violet by figuring out that violet light is striking the blue sensors and adding a little bit of red to create a purple color (purple is a mixture of red and blue, not a spectral color like violet, although they look similar to us). But film is an analog medium with no computer processing to try to match colors outside its sensitivities, so how does film actually record violet objects, and can it even do so, or do they just come out looking deep blue?

Thank you so much!
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#2 David Mullen ASC

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Posted 03 June 2011 - 01:09 PM

Certainly have seen purple before, and since film can get UV haze, clearly it is sensitive to wavelengths higher than visible blue.

I remember when the Fuji 500D "Reala" stock came out, the addition of an extra layer, sort of a green suppressant when shooting under fluorescents, had the side effect of making colors like purple render more accurately, though I'm not sure why and I don't think it's worth shooting on Reala just for that reason.
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#3 Simon Wyss

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Posted 03 June 2011 - 02:00 PM

I know that digital cameras can fake violet by figuring out that violet light is striking the blue sensors and adding a little bit of red to create a purple color (purple is a mixture of red and blue, not a spectral color like violet, although they look similar to us).

Very good question!

A film layer can be sensitive to ultraviolet, violet, and longer wave-length colours but multilayer colour films bear filter layers plus they cannot reproduce violet by their dyes. Nobody has ever seen violet on a cinema screen.

That’s the mystery of the simple thing. The secret of everything boring. The holy oafishness.
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#4 Ben Syverson

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Posted 03 June 2011 - 03:50 PM

Look at the spec sheet for any color negative film. There's plenty of sensitivity in the violet range of the spectrum.

Saying "nobody has ever seen violet on the cinema screen" is totally absurd. What about The Joker in the Batman movies? What about that scene in The Game that's shot entirely in black light?
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#5 Simon Wyss

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Posted 03 June 2011 - 04:10 PM

Violet, not purple, not lilac. Violet does not contain any red, not a trace. I cannot put up violet here for you in the forum, nor on any monitor. It would take an extra dye on the film to project it. It’s sometimes done with art imprints, seldomly, as a fourth colour.
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#6 Ben Syverson

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Posted 03 June 2011 - 07:32 PM

Violet, not purple, not lilac. Violet does not contain any red, not a trace. I cannot put up violet here for you in the forum, nor on any monitor. It would take an extra dye on the film to project it. It’s sometimes done with art imprints, seldomly, as a fourth colour.

I have to call bullsh*t on this.

Here's your eye:
Posted Image

Here's Portra 400 (similar to Vision stocks):
Posted Image

According to Kodak, color negative film is far, far more sensitive to "violet" than your eye. Please do not spread misinformation about film.

Edited by Ben Syverson, 03 June 2011 - 07:35 PM.

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#7 Brian Pritchard

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Posted 04 June 2011 - 03:00 AM

The colours that any three colour RGB system can display is entirely determined by the dyes, phosphers or LEDs. If you plot the three dyes, phosphers or leds on a CIE diagram you get a triangular shape. The only colours that system will display are contained within the triangle. In the diagram attached some generic Kodak film colour dyes are shown. The horseshoe shape shows the pure spectrum colours. You cannot reproduce the pure spectrum colours using a three colour system. If the violet you want to record and display lies out side the colour triangle then you cannot reproduce it. This applies to film, monitors, inkjet printers and paper prints using three colours.
Brian
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#8 Keith Walters

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Posted 04 June 2011 - 03:18 AM

I have to call bullsh*t on this.

Here's your eye:
Posted Image

If you look closely you will see that the red sensitive cones also have a small response in the near-UV spectrum. True monochromatic violet light will thus stimulate both the red and blue cones, which is why the same colour sensation of violet can be synthesized with a mixture of red and blue light.
However it's not really practical to design either a film emulsion or a silicon TV imager to produce a similar response.
So even though the emulsion is sensitive to true violet light, this simply comes out as blue on the print.
However if the "violet" light is actually produced by a mixture of red and blue light (which ironically is how the colour of the 'violet' flower is actually produced), then that will be reproduced accurately.
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#9 Keith Walters

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Posted 04 June 2011 - 03:27 AM

You cannot reproduce the pure spectrum colours using a three colour system. Brian

You can get very close if you use three monochromatic (or near monochromatic) light sources. LED-backlight monitors using RGB LEDS (not the cheaper white LEDS) can produce extremely vivid colours, because for example, if only the Red LCD shutters are opened, all you will see is a single wavelength Red. By switching in different amounts of the other two light sources you can dilute the colour all the way down to white, but if your light sources aren't spectrally pure, there is a limit to how saturated the colour can be.
That's why the latest digital projectors use lasers for the light sources.
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#10 Hal Smith

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Posted 04 June 2011 - 07:16 AM

As Brian pointed out: If any color's shade and saturation levels are outside the gamut of a given reproduction system, then those colors CANNOT be reproduced accurately. Film may be sensitive to violet but printed or displayed it will reproduce violet as a shade of blue or purple, not violet.

Have you noticed that rainbows don't look right reproduced on film and video? That's because rainbows contain colors that are outside of their reproduction gamuts.

If you want to test this information: Get some Rosco #59 gel, the original Congo Blue, now called Indigo. Use it to gel an HMI running without it's UV glass (obviously keep the light away from people and animals). Run a film and/or video test. Now view the results on a display or screen, it won't look anything like your eye saw it because much of the blue/violet energy in Congo Blue is below 420nm and therefore not faithully reproduced by film and video systems because their blue spectrum color is above 420nm.

I lit the Ice Storm scene in a production of "Driving Miss Daisy" with R59 in front of my Cyberlights. It actually scared audience members when HOKE comes in through the kitchen because he literally appeared out of nowhere. Apparently the eye's response to a true indigo is somewhat of a step response, either you see something...or you don't, nothing in between. As a result, HOKE appeared as if he had been sent onto the stage by a Star Trek Transporter. Did I know that was going to be the effect of that lighting? No. Did I take full credit for my real time VFX? You betcha!

Posted Image
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#11 Ben Syverson

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Posted 04 June 2011 - 11:02 AM

The colours that any three colour RGB system can display is entirely determined by the dyes, phosphers or LEDs.
Posted Image

And as you can see, violet is covered well—look down at the 400nm corner.

So... I don't understand what this debate is about. Very pure violets can be captured and reproduced on film.
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#12 Ben Syverson

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Posted 04 June 2011 - 11:15 AM

Here is that generic dye gamut overlaid on top of the Adobe RGB gamut. It speaks for itself.

Posted Image
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#13 Simon Wyss

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Posted 05 June 2011 - 03:24 AM

Ben, let me put it like this:

Black-and-white or color film can and will capture violet.

Subtractive color positive film, subtractive printing, subtractive LCD, additive fluorescent VCR tubes, additive LED arrays, additive LASER projection, and any other system will not display violet unless this specific light colour is introduced either by a filter (subtractive) or a source/luminophore (additive).

Still another point to consider is transmission from a color negative to positive stock. Had we the corresponding value of violet on the neg, an unknown yellow, would the pos stock produce violet from it?

But what gives me a real feeling of b. is the confusion about hues and their names.
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#14 K Borowski

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Posted 05 June 2011 - 10:00 AM

After being bashed for correctly pointing out the correlation between gamma and color saturation in the last thread to which I contributed in this forum, I have just read this thread and all its erroneous responses, excessive amount of verbage and charts with a laugh.


I won't bother myself to post my OWN image, as my Phtoobucket account I don't even remember a password to activiate it and upload a scan.





But, Jesus, guys, this htread is full of complex math backing up mostly false statements. Photographic blue IS violet. Don't believe me? Get F___ed. But I'll send an e-mail with the charts to prove it to anyone on here who has easy access to photobucket or another file posting method. Looks like all of you have too MUCH free storage space with all of this needlessly compllicated color science on this thread.

Photographic blue is a mixture of cyan (blue we normally speak of is dark cyan with less saturation and more density/absorbance) and MAGENTA. It basically is violet or purple, and CMY systems (like film) should be perfectly capable of communicating this color back combining cyan and magenta pigments.
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#15 Ben Syverson

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Posted 05 June 2011 - 11:10 AM

You were right in the last thread, and you're right in this thread: violet CAN of course be reproduced via film.
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#16 Hal Smith

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Posted 05 June 2011 - 03:26 PM

Since we're getting insulting: Read up on color science and gamut.

If a color is NOT in the reproduction gamut of the end to end system you're using, be it Vision print film, LCD/Plasma/CRT, Crayon, oil paint, finger paint, whatever you're not going to see the true color. Violet is at the extreme end of what the eye can perceive, and just as you and I can't see ultraviolet because it's too high in frequency, 99% of the reproduction systems out there can't reproduce a true violet. They just don't have the ability to display that high of a frequency (AKA short wavelength).

An analogy would be the human eye versus infra-red capture media. They can see IR, we can't. IR is outside of our eye's capture gamut. You can record IR on film or sensor and then reproduce it within the visible wavelength spectrum of the eye...but that doesn't mean you're directly perceiving IR. Similarly, you can record true violet on film and then reproduce it as a shade of blue or purple...but you're NOT displaying a true violet.
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#17 K Borowski

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Posted 05 June 2011 - 03:29 PM

Thanks Ben for having my back when everyone else was gathering to watch me get smashed after being thrown under the bus!


Really hard pill to swallow at the end of 16+ hour days. Not working a film shoot right now, but it's kind of like the "Happy Gilmore getting in shape for hockey season" treatment I am undergoing right now, but getting in shape for summer shooting instead :-D


If you can find a copy of the chart online, looked for it there but couldn't find it. Or could I just e-mail a flatbed scan of my '72 Kodak Color Reference chart to you to post?


I really do need to take care of Photobucket, but I have five packages to mail and some fair-wage activities to attend to.




Keep shooting film everyone!
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#18 K Borowski

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Posted 05 June 2011 - 03:35 PM

Hal, I wasn't singling you out, but if you want to take it personally, feel free to do so. I am guilty of getting overly technical with my insistence on perfect processing control (by *perfect* I mean I think what a 1-sigma deviation plus or minus, one sixth of an F/stop with Eastman Color Negative), but there comes a time when you ahve to roll the camera, and put away the calculator or the light meter or the P-cam App.


The only way one would be able to produce any color OTHER than cyan yellow or magenta would be with some sort of technicolor printer or special-built projector (neither of which is going to happen).

So the only area where this could occur today would be in offset printing where they can reproduce, at extra cost, specific colors by special mixing inks. Even here thee are mixtures of other dyes.



I don't know why CMY as opposed to actually haveing Violet (C and Y aka Blue) is a big deal. The HUMAN EYE doesn't have that exact point of sensitivity, so it is a combination of two different types of cones anyway.



Edit: And since you want me to "read up" on color science and gamut, I will tell you that I don't have to. I actually get PAID TO WORK WITH IT. No I won't post charts, provide photos as proof. CMY, RGBCIE-1966, and LAB are a few that I work with. Really enjoy Cineon, as it correlates hit points on the densitometer to values in photoshop.

Edited by K Borowski, 05 June 2011 - 03:38 PM.

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#19 Ben Syverson

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Posted 05 June 2011 - 04:15 PM

What Karl just posted is really the key. Is it possible to 100% reproduce the spectral energy of a color, using only RGB/CMY? No.

Take the example of a cup full of ultramarine pigment, illuminated by sunlight. Even with such a simple and pure setup, the pigment will reflect distinct spikes in different areas of the spectrum. Any three component imaging system decimates the spectrum to just three overlapping zones. So whether it's film or digital, the reproduced color will be some mix of R,G,B instead of that original highly complex spectral "signature."

In other words, color reproduction is a hack. It's a trick. It's lossy compression. Whatever you want to call it, it works because our eyes operate in a similar way, with three broad zones of spectral sensitivity. Our eyes can't tell the difference between the rich spectrum reflected by a red shirt in daylight and the same color simulated with different percentages of Red, Green and Blue lasers. Our eyes aren't spectrometers.

So that's why this "you can't reproduce violet" nonsense is such nonsensical nonsense. First of all, there is no color standards board to specify what "violet" is. What are we even talking about? A pure spike in the spectrum at 400nm? Are we arguing that the spectral response of a CCD/CMOS is closer to the eye's spectral response than what can be achieved with color negative? They're both imperfect. The question itself is ill-defined, which is why this debate is so inane.

The bottom line is: film and digital can both capture "violet," however we define it. The exact mix of RGB/CMY produced will be different for every emulsion or sensor. We can argue till the cows come home about which is more "accurate," but if we're really getting this pedantic, they're both inaccurate. Yet they both can produce a color which is perfectly acceptable to our eyes as "violet".

Edited by Ben Syverson, 05 June 2011 - 04:18 PM.

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#20 Hal Smith

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Posted 05 June 2011 - 05:19 PM

A pure spike in the spectrum at 400nm?


Yes.

Another parallel subject is the accurate capturing of skin tone, prop, costume, and set colors under lighting with poor spectra like many LED's. That very subject was tested in depth by the Academy. Very talented designers were shocked to discover just how bad the end to end system's reproduction of colors was when projected on screen. Why was the reproduction so bad? Because with serious holes in the lighting's spectra there were pigments in the subject's lit that were all practical purposes invisible to the lighting.

If the reproduction system can't reproduce a true violet...It ain't gonna be there. Now talented designers can fudge the colors used so that the end product looks like something people might call violet, but if you compared that violet against the original the difference would be absolutely obvious.

Back to my example of lighting a black actor with a true, close to monochromatic, violet (thanks to Congo Blue gel, MSR/HMI discharge lamps, and some additional help from my Cyberlight's built-in dichroic filters). The appearance of that combination on stage was something no one in the audience had ever seen, to the extent that it was startling to some people.
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