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Author Topic: Is accurate color possible in non-standard light?  (Read 12508 times)
torger
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« on: October 03, 2013, 02:09:58 AM »
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Help me out with some color management basics;

As far as I understand most systems are calibrated for some standard light, say daylight or flash, 5500K or so. With that kind of illuminant I guess it's possible to get accurate colors out of most cameras with appropriate profiles

However, what happens if you shoot in the dusk or dawn, or like me in the winter above the arctic circle, the color temperature of the light is then far from the standard 5500 or 6500K. I have a hunch that this affects how the eye/brain experience colors so you would need some other color model for these temperatures in order to make a calibration to accurately support that. Is there such a thing, or is accurate color management locked to illuminants close to 5500K?

Why would I want to have accurate color in extreme color temperatures you ask? If I could I would, I love to have "neutral" as a starting point when I process my pictures, but I have noted that for these light conditions it's not easy. I'd just like to know if it's possible with current technology and color models.
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ErikKaffehr
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« Reply #1 on: October 03, 2013, 02:50:37 AM »
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Hi,

I don't think accurate color is possible in any light...

In general, I think white balance is most important. Just getting it right helps a lot, but a surface in shadow or sunlight will have a different white balance, in many pictures you have both.

Sometimes a color profile for specific lighting can be helpful, but we still have metameric issues. To produce accurate colora you would need a well defined target with the same spectral response for each color as in your subject, spectral data for that target and a program generating accurate profiles from arbitrary data.

Best regards
Erik



Help me out with some color management basics;

As far as I understand most systems are calibrated for some standard light, say daylight or flash, 5500K or so. With that kind of illuminant I guess it's possible to get accurate colors out of most cameras with appropriate profiles

However, what happens if you shoot in the dusk or dawn, or like me in the winter above the arctic circle, the color temperature of the light is then far from the standard 5500 or 6500K. I have a hunch that this affects how the eye/brain experience colors so you would need some other color model for these temperatures in order to make a calibration to accurately support that. Is there such a thing, or is accurate color management locked to illuminants close to 5500K?

Why would I want to have accurate color in extreme color temperatures you ask? If I could I would, I love to have "neutral" as a starting point when I process my pictures, but I have noted that for these light conditions it's not easy. I'd just like to know if it's possible with current technology and color models.
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stamper
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« Reply #2 on: October 03, 2013, 03:25:14 AM »
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I agree with Erik's first sentence. I think too many photographers waste their time in pursuit of "accurate". I read a few days ago in a thread in the site that the colour cards on sale aren't all the same with regards to "accurate" colour, so which one should I buy? Regarding the poster's question then if he still wants to pursue it then importing the image into PS and searching for a mid grey with the colour picker and averaging the result by moving the colour channels in curves will neutralise any cast, but is it worth it?
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BartvanderWolf
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« Reply #3 on: October 03, 2013, 03:30:59 AM »
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Help me out with some color management basics;

As far as I understand most systems are calibrated for some standard light, say daylight or flash, 5500K or so. With that kind of illuminant I guess it's possible to get accurate colors out of most cameras with appropriate profiles

Hi,

Yes, within the limitations of a tri-chromatic color sampling model. There will always be trade-offs in accuracy, and there will be issues with transitions between the three bands. It's also important to remember  that a color temperature represents a continuous spectrum of light, one that resembles the emission of a so-called 'black-body' emitter of said temperature in Kelvin.

The other complicating factor is with the subject colors, some of which may be metameres which may look different depending on the spectrum of the illuminant.

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However, what happens if you shoot in the dusk or dawn, or like me in the winter above the arctic circle, the color temperature of the light is then far from the standard 5500 or 6500K. I have a hunch that this affects how the eye/brain experience colors so you would need some other color model for these temperatures in order to make a calibration to accurately support that. Is there such a thing, or is accurate color management locked to illuminants close to 5500K?

As long as we consider pure color (continuous/incandescent light, pigments, dyes), changing the whitepoint will be something that can be handled mathematically quite well, with some chromatic adaptations. But as soon as we introduce metameric color or filtered emission spectra, things get a bit less accurate. When high accuracy is needed, it becomes inevitable to calibrate for those lighting circumstances, but metamerism and a tri-chromatic color sampling will continue to be an issue.

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Why would I want to have accurate color in extreme color temperatures you ask? If I could I would, I love to have "neutral" as a starting point when I process my pictures, but I have noted that for these light conditions it's not easy. I'd just like to know if it's possible with current technology and color models.

I also like to get a neutral starting point. Not to eliminate e.g. the colors of a sunset, but to eliminate e.g. strange magenta aberrations which are caused by our imperfect color models, before I dial some color temperature shift back in.

There are also vision related complications, e.g. due to absolute illumination levels, and the way we see simultaneous contrast and color. That's something that a more perceptual CIECAM model can address better than a simplified color temperature and tint model can. Cliff Rames published a Photoshop plug-in which allows to experiment with that. RawTherapee supports some CIECAM functionality as well.

So, it won't be possible to get it accurate due to the limitations of our tri-chromatic sampling and spectral discontinuities and imperfections, and how human vision functions, but we should be able and get within the ball-park. If necessary one should profile for the actual situation, but creating accurate profiles is not that simple either, especially outside of a controlled studio environment.

Cheers,
Bart
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torger
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« Reply #4 on: October 03, 2013, 03:44:08 AM »
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In extreme color temperatures I think that the regular "daylight" white balance often produces a quite realistic result, as it will simulate the effect when the brain does not fully compensate for the extreme color temperature (ie something that appears white under daylight does not look white any longer).

Setting the white balance from a grey card won't work, because in these extreme temperatures the eye/brain does not fully adapt and I can see that the grey card looks blueish or reddish or whatever.

I've attached an image from a challenging situation, it's shot during the winter some time after sunset with a 5D mark 2. The light was extremely soft with very low contrast, and the eye did not experience the snow as "white", but as colored by the colored sky. The images from this shooting session was very hard to get right so it looked like my eye's impression on the scene. I tried various profiles from various converters, but I ended up using standard color matrixing because it more closely resembled my memory of the colors. I shot over a few hours and all the time the light was changing as the color of the sky was changing, so a shot made just 40 minutes earlier had quite different color.

If I had not processed the images so closely after I shot them, it would have been hard to make the proper color decisions. I'm quite sure that I got this image closely resembling the "reality", but some other images were much harder.

In these situations I'd prefer to have some better color management method than "process as soon as you can after the shot, and try to recreate from memory by trying various profiles and settings".
« Last Edit: October 03, 2013, 03:45:54 AM by torger » Logged
torger
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« Reply #5 on: October 03, 2013, 03:55:23 AM »
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by the way: I'm totally aware of the extreme challenges of mixed artificial light, narrow band lights being the worst. But I thought that maybe for the broad band before/after sunset sky light there could maybe exist color models that could work.
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hjulenissen
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« Reply #6 on: October 03, 2013, 04:15:14 AM »
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Setting the white balance from a grey card won't work, because in these extreme temperatures the eye/brain does not fully adapt and I can see that the grey card looks blueish or reddish or whatever.
...
In these situations I'd prefer to have some better color management method than "process as soon as you can after the shot, and try to recreate from memory by trying various profiles and settings".
It is my understanding that "color profiles" effectively attempts to relate the non-standard spectral response of a given camera to something more like a (standardized model) of our eyes - valid ideally for one set of illuminants (realistically more if both illumination and camera spectral sensitivity is smooth). Assuming that the spectral response of our photoreceptors is constant, one might hope that this is a good thing for any scene where you wish to recreate human perception?

While White-balance conceptually is a subsequent process that attempts to "replace" the illumination of the source scene with that of the destination scene. For scenes where the illumination is part of the joy, and not something that you want to get rid of, the WB concept seems kind of redundant.

To really recreate such a look, you would need a self-radiating image (such as an LCD monitor), not a reflecting print, would you not (furthering the though of recording and recreating the spectral distribution with little perceptual adjustment)?

-h
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ErikKaffehr
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« Reply #7 on: October 03, 2013, 04:33:38 AM »
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Sorry,

I was really responding to the subject line and not the entire posting. I'll try to read the entire posting next time.

Best regards
Erik

by the way: I'm totally aware of the extreme challenges of mixed artificial light, narrow band lights being the worst. But I thought that maybe for the broad band before/after sunset sky light there could maybe exist color models that could work.
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Floyd Davidson
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« Reply #8 on: October 03, 2013, 04:50:42 AM »
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Setting the white balance from a grey card won't work, because in these extreme temperatures the eye/brain does not fully adapt and I can see that the grey card looks blueish or reddish or whatever.

The problem is making a choice of which "accurate" is the one you want.  What your eye can see is one definition of accurate, but that's different than what can be measured, and both are different from what may look best on a  photograph.  To record what you saw does require processing while the memory is fresh.

At lower latitudes the significance is not as obvious.  "High noon" differs from mid-afternoon, and the Golden Hour lasts about an hour.  It's not so simple at high latitudes. In June my Golden Hour takes up maybe as much as 8 to 10 hours.  It's the mid-day period that is short!  In December none of that happens, and the bluish light of shade in failing civil twilight is all there ever is.  We get approximately the same light as everyone else about twice a year, at the equninox.

I want the "best" color for a dramatic photograph. I might process half a dozen consequtive shots to have a different color of sky behind the same bird, as an example.  I want the bird to stand out, and if different contrasts or color balance help with that, so be it.  That is very different than what you are targeting.

By the same token, your attempt at what you saw and my attempt at what I think is pretty are no better than the next guy wanting whites that are white, reds that are the same red everywhere, and so on.

All three types of "accurate" become more technically complex under more variations in light.  Starting at sub-Arctic latitudes that begins to become very significant and is increasingly so above 64 degrees.  There are no simple solutions.

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torger
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« Reply #9 on: October 03, 2013, 05:30:09 AM »
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Sorry

I was not reacting to that Smiley, I said that to try to narrow down the discussion to a case that might(?) be solvable.
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torger
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« Reply #10 on: October 03, 2013, 05:48:49 AM »
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There are no simple solutions.

That was what I was guessing Smiley. In technical terms that the experiments that have been made and standardized to create the color models we have do not include how the brain/eye experiences "extreme" color temperatures.

It probably would be possible to make such experiments and derive a color model for various types of lights, so you could when out in the field have some sort of spectrophotometer to measure the ambient light more precisely and apply the appropriate color model. Would still not work in mixed light, but could work in the example picture I posted earlier in this thread.

From an artistic standpoint I'm kind of getting bored of the typical saying "I have printed this landscape photograph not to represent what I saw, but what I felt", to me that's just another way of saying "I have manipulated this picture to make it look like I would have liked it to look". I have nothing against those that have this style, landscape photography has no documentary rules. But for myself I'd like to try a new concept, having colors that actually just as "dull" and toned down as in real life, I've figured out that since noone is doing it, it would be a pretty unique style ;-)

The ability to modify color today is so high that I feel that when I see fantastic light and color in real life it's not as exciting to capture it as I know a similar popping color could be post-processed from a duller base. However if I really had the ability to capture true-to-the-eye colors under most conditions I could have my own set of "dogma" rules that limits me how much I'm allowed to push processing.
« Last Edit: October 03, 2013, 05:56:06 AM by torger » Logged
Tony Jay
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« Reply #11 on: October 03, 2013, 06:01:55 AM »
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I have to agree with the general gist of Floyd's arguement.

For colour to be accurate one has to have a reproducible standard to compare it to.
Then there has to be a compelling reason to make the colour reproduction accurate (to the reproducible standard).
In the case of the posted jpeg "correcting" the colour to some supposed standard is nonsensical because the entire aesthetic of the image is based on the fact that parts of the scene that colour correction might render white or a shade of gray are in fact beautiful delicate pinks, blues, and purples.

Perhaps there really is some standard that will allow one to colour correct an image like that but it is likely that the result would look truly horrid and artificial.

If one is doing product or food photography then shooting in a controlled environment with light of predictable spectral characteristics and doing colour corrections in post is a no brainer.
Shooting outdoors one is looking for unusual light that, either for practical or aesthetic reasons, should not or cannot be corrected because the result will look either boring or horrid.
Best to rely on your eye and your memory in these cases.

My $0.02 worth

Tony Jay
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torger
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« Reply #12 on: October 03, 2013, 06:26:20 AM »
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I think there may be a confusion of what I mean by "correct" or "accurate" color. Forgive me I'm new to color management, but to me I see the eye/brain as the reference, ie correct color for extreme color temperatures should be how the eye/brain responds in that light, not how the objects would have appeared in noon daylight.

In other words, if I shoot a color checker in that dusk arctic light and make a profile that renders the white as white etc I don't consider that as "accurate" color as you're not representing how the eye/brain saw the original scene. The eye/brain only "white balances" within a reasonable range of color temperatures, at extreme temperatures it can even out some but not totally white balance, eg the snow is no longer white as it was at midday.

If I were a color standardization organization I suppose I could measure some different lights with a photospectrometer, recreate that under lab conditions, gather some test persons and have them do color matching tests so one could standardize how the eye/brain experiences color under certain lighting conditions. Maybe these tests would be plagued by all sorts of metamerism issues, I don't know.

My original question was if there already is such a thing, ie if there are tools today that allow you in a reasonably accurate way render colors how the eye/brain experienced it at the scene for "extreme" color temperatures, or if the way you have to do it is to try remember how it looked like and then recreate as good as you can in your raw converter.

Maybe if I just could set an "off-white" balance it could bring me far, that's generally how I do it now manually. I white balance the picture but let the white have the color cast I remember it had, usually by trial and error of color temperatures and tints until it looks sort of right. But sometimes I just feel lost. "Is this too blue? Or too little blue?" etc..., especially when there's been some time from the shoot until I process.
« Last Edit: October 03, 2013, 06:28:34 AM by torger » Logged
hjulenissen
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« Reply #13 on: October 03, 2013, 06:40:17 AM »
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Given that you experienced a certain visual impression that day.

If somehow, a wide-angle image could be recorded where at each pixel, a highly accurate estimate of the light intensity for each of a set of narrow passbands (e.g. 10nm from 400nm to 800nm) and recreated. Given that the recreated image was rendered filling your entire field of view (using a large curved projector screen or some goggles). I believe that this might be possible, if not practical, by using a colour-wheel and multispectral imaging/DLP projection along with some tinkering for stationary objects.

Would we not expect to be able to recreate that same visual impression? Excluding the inevitable "subjective" factors of freezing your behind off, being on a skiing trip etc.

If the scene can be recreated by the (impractical) means above, what does it say about the available (practical) solutions that fails to do the same?

-h
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stamper
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« Reply #14 on: October 03, 2013, 06:40:41 AM »
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The fact that you are asking so many questions about this issue should mean that in reality it isn't possible?. Concentrate on what is "pleasing". At the end of the day if you colour correct an image and it pleases you you should then be happy. If you show it to someone then they won't have a clue about how the original scene looked like and they won't care?
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Tony Jay
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« Reply #15 on: October 03, 2013, 06:42:52 AM »
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If there is a tool I am not aware of it.

As I mentioned before your eye and your memory are actually the best guide in this situation.
In the terminology that you are using the "correct" colour is the colour that is most aesthetically pleasing to you in the context of the overall image.
The fact that another photographer who was present might develop your image differently in post (with regards to colour) is neither here nor there. Aesthetics will be the goal.
You may favour somewhat more subdued colour, perhaps warmer hues or colder. It is your call.
There will be many interpretations that will look natural and believable to a third party.
The one that looks best to you will likely be the one that eye and memory informs is closest to what you experienced.

Tony Jay
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torger
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« Reply #16 on: October 03, 2013, 06:58:21 AM »
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Thanks for all your input.

There sure is a psychological component to color, so it's easy to get to the conclusion "why care?". People that work with artwork reproduction photography don't have this relaxed relation to color. I'm asking around if there are methods to be as anal about color as they are when you're a landscape photographer. My initial guess was that the answer is "no", and that seems to be correct. Tough luck, I'll just continue guess the best I can as I do today.

If there were methods, I'd probably use them. Why? There are two reasons. I think photography becomes more rewarding to me if I can capture and render color close to how the eye experienced it at the scene, as it makes special light more special rather than just a post-processing product. The other reason is that I often enough shoot in extreme light (arctic winter really is special) and have time pass between shooting and processing so I just get lost when post-processing and would like to have a sane starting-point.

Attached another photo from the same occasion as the first posted earlier. This was shot a little bit earlier, the mountain to the left is the same as in the first picture. The light is similar but quite different, the sun is still just above the horizon. I remember that for this photo I had quite a lot of difficulties to render color that felt true to what I had seen, it was easier with the photos shot just 30-40 minutes later when the sun was down.
« Last Edit: October 03, 2013, 07:06:55 AM by torger » Logged
BartvanderWolf
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« Reply #17 on: October 03, 2013, 07:25:50 AM »
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The fact that you are asking so many questions about this issue should mean that in reality it isn't possible?. Concentrate on what is "pleasing".

Frankly, that is IMHO a bit evasive. It may not be possible to do it exactly accurate, but we may still be able to do it somewhat accurate. We know that our camera, even under optimal conditions, doesn't create an exactly accurate color image. If it did, then color temperature would be exactly the same as the (incandescent) illuminant emission, and tint would be zero. And even then, metameric color may look different than it does under a different color temperature, and ambient reflections may create a local color cast.

So, what would be useful is to be able and eliminate the obvious tint errors, as much as possible, if they can be attributed to the illuminant. Then, and then only, can we adjust towards 'pleasing' rendering (whatever that may be for an individual observer), also taking local ambient color reflections into account.

The real challenge is in determining the correct White balance for the main illuminant, usually with only our inaccurate tri-chromatic sampling device/camera to measure it with. We either have to rely on reflection from objects in the scene, which may fail due to non-uniform spectral reflection, or on the main light source which may be filtered or has a deviating emission spectrum.

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At the end of the day if you colour correct an image and it pleases you you should then be happy.

That seems a bit of a circular reasoning to me, the colors are pleasing when they are made pleasing. The OP was wondering if there is a more objective way to arrive at that goal. Since there may be many pleasing renderings possible (also depends on (lack of) taste), why not pick one that is at least somewhat accurate?

I think that (if possible) a WhiBal or ColorChecker or other spectrally neutral reference object that is directly illuminated by the main illuminant (or its reflecton, e.g. blue sky in shadows) can help to eliminate most of the (tint) inaccuracies thus leaving our sense of taste or creativity to give it a spin which is at least founded on a stable/believable starting position.

When I want to create e.g. a pleasing sunset image, I know that the balance between shorter and longer wavelengths is distorted in a somewhat predictable manner. I do not want other color casts to dominate that image if my goal is to approach a somewhat accurate representation of that scene. From there it is still possible to adjust saturation or color temperature, but then that won't boost inaccurate tint influences. It basically takes part of the guesswork out of the equation.

Cheers,
Bart
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digitaldog
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« Reply #18 on: October 03, 2013, 09:21:12 AM »
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The problem is making a choice of which "accurate" is the one you want.  What your eye can see is one definition of accurate, but that's different than what can be measured, and both are different from what may look best on a  photograph. 
Exactly. We can use the term accurate and colorimetry (the measurement of color) together and a room filled with people viewing the results can say it doesn't look 'accurate'. The term accurate has to be defined. It has to be ignored as a color management sales and marketing buzz word.
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Andrew Rodney
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torger
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« Reply #19 on: October 03, 2013, 09:55:33 AM »
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Exactly. We can use the term accurate and colorimetry (the measurement of color) together and a room filled with people viewing the results can say it doesn't look 'accurate'. The term accurate has to be defined. It has to be ignored as a color management sales and marketing buzz word.

It seems like you are avoiding or missing the central question. I guess it was a mistake by me to use the word accuracy, as it draws attention from my question.

Let me rephrase. There are color models and methods that try to achieve some sort of well-defined color reproduction in controlled situations, used in for example art reproduction. When you photograph a painting for posterity you don't want it to be some personal taste of the photographer that decides how the colors are rendered. Instead you want to have some standard based on experiments on the color-seeing population so you will render something that is close to the colors most people see when they look at the original painting. You're an expert at this so you know all about it.

Now, what I'm asking is if there are similar or alternate methods to use when working in extreme color temperatures such as when shooting an outdoor landscape in arctic winter in dusk or dawn. A challenge here is that the color temperature is so extreme that the eye/brain does not compensate fully, the once white snow is no longer white, thus if I want to reproduce a photograph as realistically as possible I should not fully whitebalance the snow, but let it be off-white in the same way as people experienced it at the scene. As far as I know the only way to achieve this with today's tools is to use your memory and guess, no color management tools exist to help you choose a reasonable cast for your white to make your photograph be a realistic representation of the eye's experience at the scene.

From this discussion it seems that my assumption was right -- that there are no such methods, and all color models which strive for some sort of accuracy (or realism perhaps is a better word) work in a fairly narrow color temperature range. Ie, landscape photographers working in dusk or dawn and wanting realism must trust their good color memory and post-processing skills. So I'm not missing out on some color management method I as a landscape photographer should know about, which was my main concern and the reason I opened this thread.
« Last Edit: October 03, 2013, 10:27:21 AM by torger » Logged
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