Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: Hening Bettermann on November 16, 2011, 04:07:35 pm
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The color temperature of daylight changes in a somewhat predictable way under certain conditions, such as time of the day and amount of clouds. Thus, a very rough color temperature scale can be made, like this from CambridgeInColour.com(artificial light sources omitted):
3000-4000 K Sunrise/Sunset (clear sky)
5000-6500 K Daylight with Clear Sky (sun overhead)
6500-8000 K Moderately Overcast Sky
9000-10 000 K Shade or Heavily Overcast Sky
These numbers refer to the red/yellow-blue/cyan axis.
Does the Tint (changes along the magenta-green axis) behave in a similar way?
So that it would be possible to correlate these two, say that when Temp is in the range 6500-8000, then tint is in the range +10..+20 ?
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Of course not. Daylight is generally close to planckian locus curve, and there's only a slight tint change.
http://www.ugr.es/~colorimg/pdfs/ao_1999_5703.pdf
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Thank you, Czornyj, for your answer and the reference.
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Is this information needed for editing images or calibrating a display?
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it smells like it's related to adobe lightroom based image editing.
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>Is this information needed for editing images or calibrating a display?
>it smells like it's related to adobe lightroom based image editing.
My idea is to replace the As Shot white balance by my best memory of the kind of daylight at shooting time. My raw converter is Raw Developer, I don't have Lightroom.
Good light! - Hening.
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>Is this information needed for editing images or calibrating a display?
>it smells like it's related to adobe lightroom based image editing.
My idea is to replace the As Shot white balance by my best memory of the kind of daylight at shooting time. My raw converter is Raw Developer, I don't have Lightroom.
Good light! - Hening.
Hope you have a good memory. Kelvin numbers are just a ballpark estimate in relation to the appearance of color temp cast as interpreted by the Raw converter.
I've used Raw Developer, (purchased it) but I'm not pleased with its rendering engine (I believe Lab) when it comes to trying to get "pleasing" colors only when editing. Usually RD's default rendering is a bit more realistic than Adobe Camera Raw's, my converter of choice.
I'ld suggest if the default RD preview looks neutral overall and balanced (no one color is over saturated compared to the rest) but is still just a bit dull, to increase saturation first before attempting to warm or cool with color temp adjusts.
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Hei tlooknbill
Not sure if you understand my intention. That is to come a little closer to a "theoretically correct" color. By that I mean the perceived color at shooting time. This is neither the color that would be achieved by using the grey card, nor any arbitrary "pleasing" color.
I don't find RD's default rendering dull - quite on the contrary, I find it (and it is admittedly) tailored to please - in my lexikon: over-saturated colors and over-steepened contrast. I have replaced it by my own home-made camera profiles. My images don't look good in the raw converter, and are not supposed to, because they are linear at this stage.
> Hope you have a good memory.
Alas, this is of course the Achilles heel of my intended "method". But even a rough scale like sun around noon - afternoon - near sunset - slightly overcast - heavy overcast may be more accurate than the camera's guess, as long as this guess is based on the image, not the light. Since I do landscape, the image itself often shows a bit of the sky to aid my memory. The EXIF data record the shooting time. Maybe I will in the future make field notes concerning the degree of cloudiness. So far I have used my FRESH memory, trying to establish WB the same evening or next day.
So what I plan to use is not my memory of the colors/the wb themselves. I hope to reconstruct the most accurate WB which is possible after the circumstances using a combination of time of the day and degree of cloudiness.
Good light - Hening.
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temp/tint numbers are only a rough guide. The thing that really matters to the image is the spectrum of the illumination, which cannot be summarized by just a pair of numbers. To make matters more complicated, lighting is rarely uniform over the entire scene. So, a global temp/tint white balance is really a ballpark estimate to get you started.
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So what I plan to use is not my memory of the colors/the wb themselves. I hope to reconstruct the most accurate WB which is possible after the circumstances using a combination of time of the day and degree of cloudiness.
Would be curious to see how you go about doing that. Are you going to use measuring instruments at the time you shoot the landscape, record the number and then plug those numbers into Raw Developer?
Don't know if you're aware that the eyes perceive color cast not just from the filter effect of color temp but how real objects in a landscape reflect back their spectral make up that can contrast/compliment/amplify against this overall filter color cast effect. This usually shows up as saturation, but it's never quite determined if it's from the color cast or the spectral reflectance of the object itself in a scene. This is what makes relying on memory and at the same time trying to achieve "accuracy" not a productive part of image creation.
You are performing a magic trick in an attempt to mimic the spectral reflectance of each object in the scene lit by a natural light source such as the sun. Even at high noon direct sunlight there are objects in a scene that you would think would look neutral when on inspection with regards to accuracy may have quite a warm or cool hue, but it's hard to know whether it's from the color cast (which you should see none even at this time of day if accuracy is of concern) or the objects spectral reflectance characteristics.
This is why I suggested first increase saturation. There are some complicated optical effects going on in scene reconstruction in an artificial editing environment that aren't just about color temp that can defy numbers. Color Constancy to name one.
I've started out editing images of outdoor scenes that seem to be too blue and dull and think the dullness is from the overall blue cast. Because I didn't want to get into the back and forth fiddling of color temp/magenta/green sliders, I would increase saturation first and all of a sudden the blue cast went away.
What Kelvin number would that be because the Kelvin numbers didn't change, but my perception did?
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temp/tint numbers are only a rough guide. The thing that really matters to the image is the spectrum of the illumination, which cannot be summarized by just a pair of numbers. To make matters more complicated, lighting is rarely uniform over the entire scene. So, a global temp/tint white balance is really a ballpark estimate to get you started.
Eric,
Do you think we could expect spectrally characterized cameras and spectral RAW conversion workflow in a near (or not so near), predictable future? In simple words - something that works like an i1Display Pro but has a little bit... more sensels :D? Does industry even consider such solution at all? ACR v.7-8-9 or rather 25-56-122?
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The issue is that spectrum of illumination is generally not known at time of capture. It is of course possible to provide illumination-specific presets (and profiles), but it's partly a manual process in that the user would have to pick which one to use. That's also awkward because the user generally won't know (unless he/she has some spectral instrument with them in the field!). In some special circumstances I think this can be useful, but for general photographic use, I don't think so.
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Thanks to all who chimed in.
In the meantime, it has struck me, that my "method", to the degree it could be made precise, would have the same result as using the grey card.
When I started shooting digital, I took a purist approach and set every shot to daylight. This gave trustworthy, if uncontrolled results over a wide range. But some images shot under overcast sky late in the afternoon or early summer evening were absolutely too blue for my memory.
After that, I have relied entirely on the AWB of the camera and then chosen As Shot in the raw converter. The point of departure for my current attempt was that in some cases I discovered that the simple Daylight setting in the raw converter was more conform to my (fresh) memory than the AWB/As Shot combo. I also started wondering how the tint numbers actually were made up, hence my initial question.
Czornyjs answer seemed to make things a little simpler by omitting the tint. Erics post on the contrary points out that matters are even more complex. The whole spectrum of light would need to be considered. "So, a global temp/tint white balance is really a ballpark estimate to get you started." The problem is: started with what?
The concept of mixing in saturation is all new to me, I have no idea how it fits in theoretically. What happens to color saturation, compared to "natural"?
I have no problem making an image look "natural" just by changing the WB - my problem is that it looks "natural" over a wide range, and I would like a little more precision.
- I just tried one image which was shot late afternoon and which I remember I found too blue/green when my memory was fresh. Result:
1-Strange enough, the image does not look unnatural to me today at 5200 K=as shot.
2-It becomes even more "natural" if I increase exposure by 1/2 f-stop - however, the late afternoon mood is lost to some degree.
2-My memory, now 5 years old, accepts WB up to about 7000K, if I insist, that the thing did in fact look green. 7000K is probably pretty close to the temp at shooting time.
3- increasing saturation makes the image more blue/green.
No I will not carry additional instruments. Everything that weighs has to be omitted. One problem such instruments would meet is that my shooting "biotope" these days is woodland, and there is so to speak never an unobstructed view to the light source.
Even if there was, and even if the camera had a built-in spectrometer, there would be one problem left, same as with the grey card: The "AWB" of our brain does not work 100%, and hence, no objective measurement of incident light would have to be followed 100%. But to which %?
For now, I think I will try the following: Shoot with AWB. Then set the raw converter to daylight, say 5200 K. Neglect tint. If the resulting image is in all too strong contrast to my fresh memory, I'll try to adjust temp, staying as close to 5200 K as my memory will permit.
Good light!
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The issue is that spectrum of illumination is generally not known at time of capture. It is of course possible to provide illumination-specific presets (and profiles), but it's partly a manual process in that the user would have to pick which one to use. That's also awkward because the user generally won't know (unless he/she has some spectral instrument with them in the field!). In some special circumstances I think this can be useful, but for general photographic use, I don't think so.
Very good point, thanks Eric. I'll get back to a real world ;)
Thanks to all who chimed in.
In the meantime, it has struck me, that my "method", to the degree it could be made precise, would have the same result as using the grey card.
When I started shooting digital, I took a purist approach and set every shot to daylight. This gave trustworthy, if uncontrolled results over a wide range. But some images shot under overcast sky late in the afternoon or early summer evening were absolutely too blue for my memory.
After that, I have relied entirely on the AWB of the camera and then chosen As Shot in the raw converter. The point of departure for my current attempt was that in some cases I discovered that the simple Daylight setting in the raw converter was more conform to my (fresh) memory than the AWB/As Shot combo. I also started wondering how the tint numbers actually were made up, hence my initial question.
Czornyjs answer seemed to make things a little simpler by omitting the tint. Erics post on the contrary points out that matters are even more complex. The whole spectrum of light would need to be considered. "So, a global temp/tint white balance is really a ballpark estimate to get you started." The problem is: started with what?
The concept of mixing in saturation is all new to me, I have no idea how it fits in theoretically. What happens to color saturation, compared to "natural"?
I have no problem making an image look "natural" just by changing the WB - my problem is that it looks "natural" over a wide range, and I would like a little more precision.
- I just tried one image which was shot late afternoon and which I remember I found too blue/green when my memory was fresh. Result:
1-Strange enough, the image does not look unnatural to me today at 5200 K=as shot.
2-It becomes even more "natural" if I increase exposure by 1/2 f-stop - however, the late afternoon mood is lost to some degree.
2-My memory, now 5 years old, accepts WB up to about 7000K, if I insist, that the thing did in fact look green. 7000K is probably pretty close to the temp at shooting time.
3- increasing saturation makes the image more blue/green.
No I will not carry additional instruments. Everything that weighs has to be omitted. One problem such instruments would meet is that my shooting "biotope" these days is woodland, and there is so to speak never an unobstructed view to the light source.
Even if there was, and even if the camera had a built-in spectrometer, there would be one problem left, same as with the grey card: The "AWB" of our brain does not work 100%, and hence, no objective measurement of incident light would have to be followed 100%. But to which %?
For now, I think I will try the following: Shoot with AWB. Then set the raw converter to daylight, say 5200 K. Neglect tint. If the resulting image is in all too strong contrast to my fresh memory, I'll try to adjust temp, staying as close to 5200 K as my memory will permit.
Good light!
Hening, the problem is that even if you know the correct WB value it doesn't really have to result in correct colors. Cameras see colors in a different way than human eyes, and even if we could correct them, they're rendered on a screen or paper that has nothing to do with original viewing conditions. The way we're perceiving colors is amazingly complicated and relative. So I'm afraid you won't find any simple rule here, and you have to rely on your taste, or at least X-Rite CC Passport.
Here's a couple of my favourite essays on this fascinating topic, maybe you'll find something interesting:
http://wwwimages.adobe.com/www.adobe.com/products/photoshop/family/prophotographer/pdfs/pscs3_renderprint.pdf
http://www.um.es/phi/aguirao/master/color.pdf
http://www.cis.rit.edu/fairchild/PDFs/AppearanceLec.pdf
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Hening, the problem is that even if you know the correct WB value it doesn't really have to result in correct colors. Cameras see colors in a different way than human eyes, and even if we could correct them, they're rendered on a screen or paper that has nothing to do with original viewing conditions. The way we're perceiving colors is amazingly complicated and relative.
Exactly. Having all the numbers colorimetrically correct doesn’t ensure anyone, especially the image creator, will like the rendering. Its subjective. This goes back to the recent, long and convoluted thread where the term “accurate color” was dismissed by some, (especially me) while we were told its not subjective.
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Thank you for the links, Marcin. I'll have to digest these first. I have read Karl Lange's paper before and don't quite agree with him.
In the meantime:
> even if you know the correct WB value it doesn't really have to result in correct colors.
Well isn't that exactly what I say when I write
>my intention […] is to come a little closer to a "theoretically correct" color. By that I mean the perceived color at shooting time. This is neither the color that would be achieved by using the grey card, nor any arbitrary "pleasing" color.
and
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Even if there was, and even if the camera had a built-in spectrometer, there would be one problem left, same as with the grey card: The "AWB" of our brain does not work 100%, and hence, no objective measurement of incident light would have to be followed 100%. But to which %?
Andrew, I have followed a part of that long convoluted thread, and I felt that it lacked exactly what I am trying to formulate here: a concept of the PERCEIVED color at shooting time. In that thread the 2 only alternatives seemed to be colorimetric accuracy on the one hand, and completely ad lib subjectivity on the other.
If I am fascinated by some particular color I see in nature, it is THIS color I want to reproduce, not just any arbitrary color. It can be achieved to some degree. The color I get with my home made profiles IS more accurate than RD's default rendering, even though it might be difficult to prove it in court.
I mean all calibrating and profiling and so on has just this purpose: to reduce subjectivity in color rendering, hasn't it? But I see that the WB has particular challenges.
Good light!
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I mean all calibrating and profiling and so on has just this purpose: to reduce subjectivity in color rendering, hasn't it? But I see that the WB has particular challenges.
The purpose of calibrating and profiling is to get reasonably predictable and repeatable results. To some degree it also helps to achieve pleasing and convincing colors from camera, but they'll never really match reality, reproduce the original impression as:
- you see the colors in a different viewing condition, and the change of context changes the relations of colors and spoils everything. It's like trying to reproduce the look of a print on a different paper - you'll never get the look of baryta on a newspaper.
- the camera has different spectral sensitivity than cone cells in the retina, and the spectral sensitivity of cone cells is not constant (even locally). So even if we neutralize the white balance in a part of image there may be other parts that look bad, and so or so some colors may be disorted.
- and so on...
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I mean all calibrating and profiling and so on has just this purpose: to reduce subjectivity in color rendering, hasn't it?
In theory maybe. In practice not entirely. The basis of current CMS technology is based on very old concepts, developed long before computers existed and using some very simple assumptions that often don’t jive with how we see (perceive) color. As just one example. Nearly all output profiles assume D50 illuminant. That’s a mighty big assumption. The current technology reduces complex images to solid square colors and don’t take color into context. There are issues with Lab, the color model most of the current technology uses in terms of profiling.
There are color scientists working on color appearance models that could greatly aid in getting closer to your goal. But we’re not there yet.
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There are color scientists working on color appearance models that could greatly aid in getting closer to your goal. But we’re not there yet.
Andrew, do you know where these color scientists working on this can be contacted?
I'ld just love to discuss and exchange info on the subject of color appearance as I'm sure would a lot of photographers here at LuLa and elsewhere.
Hening, I took a look at your landscape shots on your website. You really don't like saturation. I see you prefer the 'natural' look. The scenes you captured look very similar to the type of country side around where I live in New Braunfels, Texas.
Do you find shaded brush country that bluish looking? I used to think it did until I started forcing myself to take mental notes how warm white limestone rocks appear under the forest canopy. Tree bark is at least neutral or a bit on the warm side. I get the overly pronounced cyan blue shadows and have to reduce saturation in the blue channel in ACR's HSL panel. Works like a champ.
Please don't take what I'm saying as criticism of your work. Just trying to illustrate the subjectivity of this subject.
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So what I plan to use is not my memory of the colors/the wb themselves. I hope to reconstruct the most accurate WB which is possible after the circumstances using a combination of time of the day and degree of cloudiness.
The time of day and the degree of cloudiness are a start, but one must realize that daylight (http://en.wikipedia.org/wiki/Daylight) is a combination of sunlight, skylight, light scattered from clouds, and reflected light from the ground, vegetation, and surrounding buildings (in the case of a more urban environment). The first three sources are sufficiently close to the Planckian locus that a correlated color temperature describes them reasonablly well (see Handprint (http://www.handprint.com/HP/WCL/color1.html)) for the graph reproduced from Wyszecki & Stiles, 1982 and reproduced below as well as more information. D55 corresponds to noon sunlight and D55 to noon daylight.
(http://bjanes.smugmug.com/Photography/WhiteBalance/i-RLpRvJg/0/O/LightSpectrum.png)
For illustration, sunlight is observable when a shaft of sunlight enters a darkened room through a small window which obstructs most of the skylight. Skylight is shown by light entering a northern facing window. When you mention accurate watch out for the thought police in the form of the DigitalDog :). The latter seems to prefer automatic white balance of the camera, but it will fail when the scene contains a predominant strongly saturated color and no neutrals.
As Eric stated, color and tint are a good starting point, but why not merely take a reading from a neutral card illuminated by the same light as the subject (if that is possible).
Regards,
Bill
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Exactly. Having all the numbers colorimetrically correct doesn’t ensure anyone, especially the image creator, will like the rendering. Its subjective. This goes back to the recent, long and convoluted thread where the term “accurate color” was dismissed by some, (especially me) while we were told its not subjective.
You are comparing apples and oranges. Accurate reproduction of a scene under field conditions can be difficult and may require some subjective input for pleasing results, as with a sunset. However, if I photograph an X-Rite color checker and render it into a defined color space such as ProPhotoRGB, I can compare the observed values in the file to those measured from the target by a laboratory grade spectrophotometer and determine the accuracy of the rendering and give a mathematical analysis. For more practical work, one could assume that the color checker is reasonably accurate. It helps to know the white balance for the illumination used to take the photograph. What is subjective about this?
Regards,
Bill
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As Eric stated, color and tint are a good starting point, but why not merely take a reading from a neutral card illuminated by the same light as the subject (if that is possible).
Well, I've done this adjusting color temp sliders in ACR by clicking on a WhiBal card lit by overcast cloudy light on my window sill. What I find happens is there can be a wide variation in the numbers and thus appearance of color cast adjusting the Kelvin and Green/Magenta sliders that still deliver an R=G=B readout in the card. So much for nailing it on a consistent basis.
In actuality to my eyes the WhiBal gray portion of the card has a warm-ish desaturated camel colored hue lit under this overcast light. It turns slightly blue-ish clicking for R=G=B. I used "Cloudy" as an incamera preset which gave the most accurate to scene appearance but still required white balance adjusting to get rid of the overly warm appearance.
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Andrew, do you know where these color scientists working on this can be contacted?
I’d start on Apple’s Colorsync user lists (end user and developer).
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However, if I photograph an X-Rite color checker and render it into a defined color space such as ProPhotoRGB, I can compare the observed values in the file to those measured from the target by a laboratory grade spectrophotometer and determine the accuracy of the rendering and give a mathematical analysis.
So the light source for the Spectrophotometer and the light under which Macbeth resides matches or the differences are correlated how? The Spectrophotometer provides spectral data, you could convert it into Lab presumably? Does the white point specification play any role? Because you have to end up giving us ProPhoto RGB values, it is coming from Lab right? What about the known issues (some would call them bugs, like Karl who you quoted), with Lab? If you nail ALL the numbers as everyone agrees, there’s then some issue shooting outside this controlled condition, like your sunset example?
You mention render the data into a defined color space such as ProPhotoRGB for this specific set of observable values. That’s rendered exactly how to maintain the math? What converter? Set how?
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Andrew, do you know where these color scientists working on this can be contacted?
There is lots of good stuff going on at the Munsell Color Science Lab at RIT. On of their faculty members, Mark Fairchild, has a great book "Color Appearance Models," which is a good place to start to get the gist of where color scientists are heading. It's an excellent (though expensive) book that starts from the basics of human vision and psychophysics and works the reader through some of the newer color appearance models.
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So the light source for the Spectrophotometer and the light under which Macbeth resides matches or the differences are correlated how? The Spectrophotometer provides spectral data, you could convert it into Lab presumably? Does the white point specification play any role? Because you have to end up giving us ProPhoto RGB values, it is coming from Lab right? What about the known issues (some would call them bugs, like Karl who you quoted), with Lab? If you nail ALL the numbers as everyone agrees, there’s then some issue shooting outside this controlled condition, like your sunset example?
One could use a hand held device as shown on the X-Rite site (http://www.xrite.com/custom_page.aspx?PageID=137). The Spectrodensitometer 530 would do the job and costs US $5000. It has its own light source and can produce Illuminants A, C, D50, D55, D65, D75, F2, F7, F11, F12. By the way, it has a white calibration target. It can read out directly in L*a*b. Since L*a*b is D50, I would use that illuminant to avoid problems with chromatic adaption.
You mention render the data into a defined color space such as ProPhotoRGB for this specific set of observable values. That’s rendered exactly how to maintain the math? What converter? Set how?
To measure the system color error (DeltaE) the rendering engine is not critical and one would not have to use D50 illumination for the ColorChecker. D50 bulbs are available, but in my experiments, I merely used Solux bulbs and white balanced. One is merely comparing the rendered value with the true value. For now, L*a*b is standard even though it has some issues when pushed to extremes, but the ColorChecker is not that taxing of a test. The use of ProPhotoRGB also eliminates problems with chromatic adaption, since it is also D50.
If one does not have the $5000 for the 530, he can use the published L*a*b or ProPhotoRGB values for the color checker. This would provide reasonable accuracy. You can nit pick all you want, but such measurements are done all the time and can produce an acceptable measure of accuracy for testing various camera profiles and raw converters. Color scientists could refine the test methodology.
Regards,
Bill
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Thanks, Mark and Andrew, for the tips on where to find color appearance model color science discussions.
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Well, I've done this adjusting color temp sliders in ACR by clicking on a WhiBal card lit by overcast cloudy light on my window sill. What I find happens is there can be a wide variation in the numbers and thus appearance of color cast adjusting the Kelvin and Green/Magenta sliders that still deliver an R=G=B readout in the card. So much for nailing it on a consistent basis.
Yes, there are an infinite number of spectra that can produce a correlated color temperature of 11000K or whatever your cloudy light might be. I'm not that sure that cloudy light lies on the Planckian locus, but if it does, the tint would be zero and only one temp would produce R=B=G.
In actuality to my eyes the WhiBal gray portion of the card has a warm-ish desaturated camel colored hue lit under this overcast light. It turns slightly blue-ish clicking for R=G=B. I used "Cloudy" as an incamera preset which gave the most accurate to scene appearance but still required white balance adjusting to get rid of the overly warm appearance.
Perhaps your vision was adapted to the indoor light and was not adapted to the cloudy light. Also the illuminaton was likely mixed, outdoor and indoor. As pointed out in the Fairchild article on human color vision that Marcin referenced, color constancy (the everyday perception that the colors of objects remain unchanged across significant changes in illumination color and luminance levels) is actually quite poor when careful observations are made. Of course, the scene appearance is a perception and perceptions can't be quantified. One can measure stimuli with great precision, but the appearance could only be estimated by color matching under controlled conditions. This is how the CIE determined the characteristics of the standard human observer.
Regards,
Bill
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Bill, all these measurbatory machinations you speak of may produce 'reasonably accurate' (seems you're hedging here from earlier discussions) in a very tightly controlled environment. But in the real world, where most of us live and work, the theory falls down. How do you use a 'paint by WB numbers' approach to generate your 'reasonably accurate' colour reproduction in an environment that has a wide range of lighting colour temperatures? Even in a studio, with controlled lighting there will be variations based on, as you noted, the different reflectant surfaces the light from the 'accurate' studio lights will bounce off of. As I and, more importantly, others have pointed out, things like an XRite CC are a decent starting point but there's still a level of subjectivity and adjustment that may be required to get the required or desired 'colour match' (as closely as that's ever possible) taking into account the manner in which the image is to be reproduced (e.g., screen, high gloss art paper, magazine stock), not even taking into account the luminant under which it will be viewed.
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Bill, all these measurbatory machinations you speak of may produce 'reasonably accurate' (seems you're hedging here from earlier discussions) in a very tightly controlled environment.
Of course, totally accurate results are not possible with current cameras since they have metameric error due to imperfect CFA filters, and I never claimed perfect accuracy was attainable. However, my point was that accuracy under controlled conditions with a relatively simple target (the ColorChecker) can be measured and expressed as DeltaE or DeltaC and that white balance is a critical first step. With the color checker, the WB can be read directly from a neutral patch of the target, but a neutral area in scenes in the field is often not available and it is a good idea to perform a custom white balance prior to shooting under these conditions. The camera records light reflected off the subject, and the color of that light is critical in assessing the actual color of the subject. In practical photography we are merely interested in obtaining a tri-stimulus metameric match.
But in the real world, where most of us live and work, the theory falls down. As I and, more importantly, others have pointed out, things like an XRite CC are a decent starting point but there's still a level of subjectivity and adjustment that may be required to get the required or desired 'colour match' (as closely as that's ever possible) taking into account the manner in which the image is to be reproduced (e.g., screen, high gloss art paper, magazine stock), not even taking into account the luminant under which it will be viewed.
Yes, an XRite CC used with the Passport software is useful in creating a custom profile under the existing field conditions. White balance from a neutral card is also useful. In my experience and in the experience of others (satisfied WhiBal users) a good WB reading is a very useful first step. The camera produces a scene referred image and the color accuracy raw file is of primary interest. Of course, rendering into a defined color space using an accurate camera profile is important, but this can be refined post-capture. The metric being measured in my prior posts is the accuracy of the rendered raw file as compared to the actual colors of the target which are known or can be measured if one has the equipment; the print and the illuminant under which it is viewed is irrelevant here. Color adaption of the viewer is also irrelevant.
Regards,
Bill
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We're back to the same, tired, circular discussion, Bill. What you're referring to as 'accuracy' isn't. And the world doesn't work in the theory of controlled conditions. Tim alluded to a perfect example earlier. Water flowing in a river, part in shade, part in sunlight or daylight. Where do you place the CC card? In the daylight or the shade? Put it in the shade and the daylight area will have a very heavy colour cast. Put it in the daylight and the river in shade will have a very deep colour cast. Is either 'accurate'? No. Is it even practical or possible to walk and put it in either location? Quite possible not.
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An interesting concept with regard to placing the CC chart in shade or direct sunlight would be to get two charts for each and photograph them as one image.
The question would be, if you make the CC chart look correct in the sunlit version (with a camera profile and/or edits) and let the shaded CCchart's colors fall where they may, would that shaded chart's colors deliver a colorimetrically or perceptually correct rendering? Or would there be extreme edits required maybe having to selectively edit each color patch to get it to look as it should under shaded light?
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We're back to the same, tired, circular discussion, Bill. What you're referring to as 'accuracy' isn't. And the world doesn't work in the theory of controlled conditions.
It is “accurate” when he says it is and not when it doesn’t suite the conditoins: (Accurate reproduction of a scene under field conditions can be difficult and may require some subjective input for pleasing results, as with a sunset.)
Or:
(This would provide reasonable accuracy. You can nit pick all you want, but such measurements are done all the time and can produce an acceptable measure of accuracy for testing various camera profiles and raw converters. Color scientists could refine the test methodology.)
It is reasonable, acceptable and accurate when we’re told it is. When conditions exist when it is not accurate, it’s not.
Reminds me of the analysis Bruce Lindbloom made about another specious argument with similar circular logic: If one takes this technique to its logical conclusion, Dan's 16-bit challenge would become "When considering all images showing no 16-bit advantage, 16-bit images show no advantage." Substitute accurate for 16-bit.
How accurate or inaccurate, with specific situations using any defined metric is never explained. But as you point out, we’ve been down this rabbit hole before, lets move on.
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An interesting concept with regard to placing the CC chart in shade or direct sunlight would be to get two charts for each and photograph them as one image.
The question would be, if you make the CC chart look correct in the sunlit version (with a camera profile and/or edits) and let the shaded CCchart's colors fall where they may, would that shaded chart's colors deliver a colorimetrically or perceptually correct rendering? Or would there be extreme edits required maybe having to selectively edit each color patch to get it to look as it should under shaded light?
Exactly my point, Tim. In order to get each area 'accurate' (let's assume for the sake of discussion that the neutral grey patch at R=G=B is 'accurate) there'd have to be some heavy masking and editing. But even when 'accurate' is achieved is that a desirable result?
The idea of WB accuracy also completely ignores the idea of using WB creatively.
Here's an example. I really liked the texture of the bark on this old tree. The first shot is an 'accurate' WB. It's a kind of muddled grey/brown. I knew; however, that if I used my WB creatively I could come up with something much different and, to me, much more interesting. That's the second shot. It's had additional processing to clone out a couple things, sharpen, curves, etc. Those same edits could have been made to the 'accurate' WB shot but it still would have been bleh. I'll add a second set as well. The third image is with the As Shot WB. It's pretty 'accurate' in terms of colour rendition. The grass around the trees was green and the bark of the trees was a muddled grey/brown. The second shot uses WB to creatively render the scene.
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Uff! uff! Now I have done exactly what I tried to avoid: triggered a new long and convoluted discussion, including a new show down between Andrew and Bill Janes. I consciously kept my question out of that thread, even if it belonged in the context. I deliberately presented my innocent little question without mentioning what I wanted to use the answer for. And now…Posts keep coming faster than I can reply. This one belongs after post #19.
First off: Many thanks to all of you for your concern.
@Czornyj:
The limitations you mention in post #16 are obviously all true - but yet, on one and the same paper or screen, some renderings look more natural than others. I am aware of that what I try/tried to achieve can only be a very rough approximation. It is/was just a first attempt to come up with an alternative to an AWB - which on its part suffers from the very same limitations. And then some: If I understand it right, it has by definition to assume an average color balance, and try to achieve that.
I would like to share a key experience which greatly confirmed my suspiciousness towards automatisms - if that was ever needed. - In the days of film, I took 2 images of a scene in northern Sweden, one around noon, one shortly before sunset. As exspected, the transparency of #2 was much more red than #1. Later, I had these 2 images scanned on an Imacon. In the default rendering of the Flexcolor software, #2 was *more green* than #1! Obviously, the automatism thought "No, so much red can not be true", and obviously, it was wrong.
@Andrew
> In theory maybe. In practice not entirely.
> There are color scientists working on color appearance models that could greatly aid in getting closer to your goal. But we’re not there yet.
See this sounds much better to me than just "It's subjective."
@tlooknbill
With regard to the bluish: most of the images on my web site are processed after my hitherto workflow, that is shot with AWB and processed As Shot. First recently have I changed the WB to Daylight in some of them. Beyond these 2 alternatives, I have not tried to modify color in any way. I hope, that the images shown look reasonably natural. I don't find them bluish.
> Please don't take what I'm saying as criticism of your work.
I certainly don't! Your diagnosis "You really don't like saturation. I see you prefer the 'natural' look." is entirely in accordance with my self-understanding.
A little aside: Ditching your fellow Texican countryman Brian Griffith's Raw Developer for its default color rendering sounds to me like throwing away a jewel because one doesn't like the color of the wrapping paper. As said, I don't like that default rendering either - for reasons opposite to yours. But why use the default rendering? Yes, RD does not support DNG profiles, you have to make ICC profiles, and I had to learn a little bit of Unix to use Argyll for that. I find the deconvolution sharpening the trump card of RD.
@bjanes:
Thank you for this informative post.
> why not merely take a reading from a neutral card illuminated by the same light as the subject (if that is possible).
Maybe I should try that. Would it be more precise than the rough scale quoted in my first post?
The color event, I read, consists of 3 parts: the incident light, the light reflected from the objects, and my brain.
In relationship to this triangle, the photographer shooting art for reproduction, or objects for a catalogue, may try to achieve accuracy by standardizing shooting light and viewing light to make them "fall out of the equation", so that, under standard viewing light, the image will look the same as the object.
In (my) landscape photography, on the other hand, the color of the light is part of the subject - I want to catch it, not to standardize it out.
I read that my brain has some sort of AWB - but it is not 100%. I remember walking a late summer afternoon in the inner city of Copenhagen with its half-timbered white houses. In the sun of that late afternoon, these houses did NOT seem white to me, but pink. It is this pink I want to capture. The grey card method would eliminate it, wouldn't it? I think it would leave the problem: to what degree should I follow it? But I will try it.
> but one must realize that daylight is a combination of sunlight, skylight, light scattered from clouds, and reflected light from the ground, vegetation, and surrounding buildings (in the case of a more urban environment).
If I conceive the latter as the light I do NOT want to filter out (if any), then it may indeed sound like my intended "method" may not be that bad after all.
Good light! - Hening.
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FWIW and going back OT, I’m also a big fan of Raw Developer.
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We're back to the same, tired, circular discussion, Bill. What you're referring to as 'accuracy' isn't.
The Wikipedia definition of accuracy consistent with my usage: "In the fields of science, engineering, industry and statistics, the accuracy[1] of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value." This is exactly what I am doing. Comparing the measured color checker values with those of the target (either measured or per spec). What is your definition and how am I using the term incorrectly?
And the world doesn't work in the theory of controlled conditions. Tim alluded to a perfect example earlier. Water flowing in a river, part in shade, part in sunlight or daylight. Where do you place the CC card? In the daylight or the shade? Put it in the shade and the daylight area will have a very heavy colour cast. Put it in the daylight and the river in shade will have a very deep colour cast. Is either 'accurate'? No. Is it even practical or possible to walk and put it in either location? Quite possible not.
The example is a poor one, since the lighting of the scene is mixed and there are two illuminants. An accurate white balance would be for one illuminant, and two WBs would be needed for your case. You could take two shots with the proper WBs and blend them. No single white balance would reproduce neutrals as neutral in your mixed scene, which is what you want to do with WB. The camera would produce a scene referred image reproducing the two areas of the scene accurately within the limitations of the camera. A human observer could account for the mixed illumination via chromatic adaption, use of memory colors, color constancy, and discounting of the illuminant. This is where the art of rendering the image comes in, and the procedure to be followed would depend on how you wish the scene to appear in the photograph. You would probably want the sunlit area to have a neutral white balance. If you wanted the cloud lit area of the image to appear somewhat blue as it would appear to an observer with incomplete adaption, you might use a WB in that area of the image that would yield a bluish cast.
Regards,
Bill
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The idea of WB accuracy also completely ignores the idea of using WB creatively.
Here's an example. I really liked the texture of the bark on this old tree. The first shot is an 'accurate' WB. It's a kind of muddled grey/brown. I knew; however, that if I used my WB creatively I could come up with something much different and, to me, much more interesting.
I am not talking about creative use of WB, but the use of WB to produce an image that reflects how the object appeared to the eye. For example, if a botanist wished to publish the appearance of the bark in a book on trees, the first WB would probably be best, and it would reproduce the colors of the tree within the accuracy limitations of the camera, WB, and camera profile and rendering engine. Personally, I find your "creative" images to be horrendous. If one wanted to reproduce a Monet painting with the colors as Monet intended, certainly one would not want to use the BobFisher creative WB to produce a ghastly effect.
Regards,
Bill
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It is reasonable, acceptable and accurate when we’re told it is. When conditions exist when it is not accurate, it’s not.
Reminds me of the analysis Bruce Lindbloom made about another specious argument with similar circular logic: If one takes this technique to its logical conclusion, Dan's 16-bit challenge would become "When considering all images showing no 16-bit advantage, 16-bit images show no advantage." Substitute accurate for 16-bit.
How accurate or inaccurate, with specific situations using any defined metric is never explained. But as you point out, we’ve been down this rabbit hole before, lets move on.
The Bruce Lindbloom analogy is specious. I have explained my measurement of accuracy by comparing the color of the color checker to that obtained in the image. You just can't seem to appreciate that. And in my testing, I don't WB on obviously blown neutral areas ;D.
Regards,
Bill
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The Wikipedia definition of accuracy consistent with my usage: "In the fields of science, engineering, industry and statistics, the accuracy[1] of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value." This is exactly what I am doing.
It's still problematic, Bill, because it's not clear which actual (true) value you are trying to measure.
Consider Hening's last example of photographing white houses in late afternoon light. What does it mean to photograph or measure the color 'accurately'?
There are a couple options:
1. You could take a spectrophotometer with its built in light source and measure the houses. (Let's pretend the house paint is really perfectly neutral white for the sake of simplicity). The spectro will give you a nice flat distribution across the spectrum. In other words, white. This IS accurate in a sense—if you went to the paint manufacturer and showed an image with perfectly white houses they would say yes—that's the color of the paint. But this is not what Hennig saw and does NOT accurately describe the scene. He saw pink houses because of the late afternoon light.
2. You could measure the light reflecting from the white wall with a spectrophotometer. You'll get a totally different color that is essentially a spectral distribution of the light source. This stands a better chance of accurately describing what Hennig saw. But you have a new problem now: in order to convert that SPD into a colorimetric value you need a white point. What do you choose? The right answer is the white point which Hennig's eyes are chromatically adapted to, but you can't know that. So you are back to making a subjective choice.
3. Using a grey card is essentially the same as option one. You can neutralize the grey to its known value, but then you will have stripped the pink out of the walls and again it won't be accurate in the sense of describing the scene.
As far as I can tell, there is no objective way to reproduce Hennig's subjective experience. Only Hennig with the help of his memory can do that.
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You're missing the point entirely, Bill. It seems you're so completely caught up in your own absolute literal world that you can't see the forest for the trees. ::)
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What is your definition and how am I using the term incorrectly?
You're missing the point entirely, Bill. It seems you're so completely caught up in your own absolute literal world that you can't see the forest for the trees. ::)
Bob, why don't you just answer the question so this matter can be settled? You are not getting my point. I may not be the only one who is inflexible in their views.
Regards,
Bill
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The definition is moot. 'Accuracy' as you define it; as I have commented, more importantly as Tim and Andrew have commented, isn't a relevant metric. There is a difference between numerically accurate and a colour match (or as close as can be achieved). Scene referred 'accuracy' doesn't automatically correlate to an output referred match.
Andrew's right. We've been down this rabbit hole before. And it isn't even the good pill. ;D
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The limitations with a neutral / gray balance card are (1) it still doesn't tell you what the spectrum of the illuminant is, and (2) it doesn't compensate for the fact that the illumination can be (and often is) spatially-varying across the scene.
So, you can click-WB on a neutral reference and guarantee that its appearance within the rendered image will be perfectly neutral (e.g., R = G = B). However, that by itself guarantees nothing about the appearance of the rest of the (non-neutral) colors in the image. There are many factors that would need to be taken into account in order to get the colors in the image to be colorimetrically correct. This is generally difficult because, as indicated above, the factors are generally not known at the time of capture. Even if they are known at the time of capture (or can be estimated, or guessed, or otherwise provided), a perfect colorimetric matching is often impossible, due to mismatches in the way the camera "sees" and the way we (humans) see. And last, but not least, it has been my experience that photographers generally don't want colorimetric matching as an end result.
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And last, but not least, it has been my experience that photographers generally don't want colorimetric matching as an end result.
Because of colorimetric matching limitations, or rather because of currently actual trend & fashion in photography?
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No I will not carry additional instruments. Everything that weighs has to be omitted. One problem such instruments would meet is that my shooting "biotope" these days is woodland, and there is so to speak never an unobstructed view to the light source.
IMHO just get a ColorRight Classic (http://colorright.com/colorright-classic.html) to take a white balance shot before a series of photos to capture a relatively accurate white balance and review on your camera on site if you trust the camera's LCD. If you needed a gray card you can use the ColorRight Classic to provide this as well by photographing it into the scene. Then in post production you can choose what white balance you prefer (as shot with custom WB, AWB, camera modes like Daylite, Nighttime etc).
Naturally it wouldn't be 100% accurate however it would be probably more accurate than post-processing it to what you remember. Even then, you could choose what white balance you preferred according to whatever criteria you wanted to make it look like what you recalled. If you needed more accuracy you'd probably need to grab a ColorChecker Passport or similar device to assist.
Reading other people's comments it could be hashed out to any number of degrees however for myself I've found a combo of the ColorRight Classic + review on-site of the image on the camera (usually right after taking the shot) itself to be beneficial for taking relatively accurate landscape photography scenes. Since this is for my own personal use I prefer accuracy over what looks "best" or "most pleasing" so I rarely bother to modify the images afterwards unless I'm specifically printing them off.
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Try raw photo processor. Its white balance AUTO is so good, it's stunning every time, and a wonderful starting point.
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@ Eric
I'm not sure if it is me whom you are addressing with your last post, but I'll reply as if it was.
> that photographers generally don't want colorimetric matching as an end result.
The example with the white/pink houses should make it clear, that I am aware of that the colorimetric correctness as obtained by the gray card method will probably not give me the color as perceived at shooting time - not (only) due to limitations of the method that you point to, but due to its principle, as I understand it.
That said, I believe that the way in which "your" photographers want to deviate from colorimetric accuracy has quite different reasons - they want something "pleasing".
> mismatches in the way the camera "sees" and the way we (humans) see:
I think my exspectations to this match are much more modest than what you have in mind. My problem is not that I can not get a match that seems close enough to me. My problem is that I find it good enough over a wide range, and I would like something that is more precise than my memory, which we all know is a rubber measure.
@PhilippCummins
The advantage I can see in the ColorRight diffuser over the grey card is that you operate it on the camera, or at arms length. The card requires to be placed in the distance of focus. Otherwise, the same considerations apply.
@ixania2
Thanks for the tip. However, I think I'll stay with Raw Developer as the raw converter because of its deconvolution sharpening.
Good light! - Hening.
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The definition is moot. 'Accuracy' as you define it; as I have commented, more importantly as Tim and Andrew have commented, isn't a relevant metric. There is a difference between numerically accurate and a colour match (or as close as can be achieved). Scene referred 'accuracy' doesn't automatically correlate to an output referred match.
Andrew's right. We've been down this rabbit hole before. And it isn't even the good pill. ;D
As a non-measurbator, you likely do not have the slightest understanding of "color accuracy" but are merely spouting off what you have read in the non-peer reviewed literature on the web. Imatest is a measurbators delight and you might gain some knowledge by looking at the ColorCheck documentation (http://www.imatest.com/docs/colorcheck_ref.html), which is prefaced by this comment:
The notation in this section is adapted from the Digital Color Imaging Handbook, edited by Gaurav Sharma, published by the CRC Press, referred to below as DCIH. The DCIH online Errata was consulted.
In measuring color error, keep it in mind that accurate color is not necessarily the same as pleasing color. Many manufacturers deliberately alter colors to make them more pleasing, most often by increasing saturation. In calculating color error, you may choose not to use the exact formulas for ColorChecker L*a*b* values; you may want to substitute your own enhanced values.
So you might refer some of your comments to Norman Koren, the author of Imatest. He has devoted considerable time and effort to measure color accuracy.
With regard to the ColorChecker, you might refer to Danny Pascale's article (http://www.babelcolor.com/download/RGB%20Coordinates%20of%20the%20Macbeth%20ColorChecker.pdf) on it and the various equations that can be used to convert between color spaces that can be used for transformations of the color values. Danny also has an excellent article (http://www.babelcolor.com/download/A%20review%20of%20RGB%20color%20spaces.pdf)on color spaces, much better than the dumbed down version given by the DigitalDog. The ICC also has a white paper (http://www.color.org/whitepapers.xalter) on measuring color accurately. When you have gained some technical knowledge, please come back for further discussion.
Regards,
Bill
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No Bill, I understand the point you're making quite well. I also understand the theory behind it. I don't care about the math. Understanding the math isn't necessary to understand the theory and use it in practical application. You disagree with that and that's fine. I simply disagree on the necessity of such a rigid workflow in all situations. And I disagree that such a rigid workflow is valuable in all situations. I've said before; and if you actually take the time to read you'd realise, that I do believe there are times when as close a scene-referred match as can be obtained is valuable. You're also, seemingly, ignoring the point that a scene-referred match doesn't correlate to an output-referred match (i.e., that the colours reproduced in the final output are a match to the colours in the original scene). To say nothing of the brightness range in the original scene that, depending on the range, may not be able to be reproduced by any output medium.
And while I disagree with the idea that an 'accuate' WB is the best way to achieve a proper scene-referred image and that a camera profile, similarly, is the Holy Grail I reference this from "Real World Color Management, 2nd Ed" by Fraser, Murphy & Bunting: "Camerra profiles are a bit more slippery. We've found that even with the best camera profiles, we'll still have to make significant edits to tone, and when camera metamerism rears its head, to color too." Further, the authors continue to state that a good camera profile is merely a 'nudge in the right direction'.
Let me ask you this, Bill. Given your strong preference for scene-referred colour 'accuracy', how did you ever operate in the film world?
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I do believe there are times when as close a scene-referred match as can be obtained is valuable. You're also, seemingly, ignoring the point that a scene-referred match doesn't correlate to an output-referred match (i.e., that the colours reproduced in the final output are a match to the colours in the original scene). To say nothing of the brightness range in the original scene that, depending on the range, may not be able to be reproduced by any output medium.
You keep talking about scene referred images, probably taking up the subject from the DigitalDog, who likes to use the term for obfuscation. However, I’m not certain that you know what scene referred actually means. A scene is defined in ISO 22028-1 (http://www.color.org/scene-referred.xalter) as:
“scene: spectral radiances of a view of the natural world as measured from a specified vantage point in space and at a specified time.
A scene may correspond to an actual view of the natural world or to a computer-generated virtual scene simulating such a view.
A scene-referred image is an image where the image data is an encoding of the colors of a scene (relative to each other), as opposed to a picture of a scene. In a picture, the colors are typically altered to make them more pleasing to viewers when viewed using some target medium.”
The definition of spectral radiance from Wikipedia (http://en.wikipedia.org/wiki/Radiance):
"Spectral radiance expresses radiance as a function of frequency (Hz) with SI units W•sr−1•m−2•Hz−1 or wavelength (nm) with units of W•sr−1•m−2•nm−1 (more common than W•sr−1•m-3). Radiance is the integral of the spectral radiance over all wavelengths."
Thus a scene referred image is in linear gamma and is essentially HDR for most normal outdoor scenes. Further the scene color data are determined by the actual wavelengths of light reflected from the subject. The raw file is scene referred within the limitations of the digital capture. If we want to reproduce the appearance of the scene, we have to know something about the illuminant, and this involves white balance.
As discussed at length by Karl Lang in Rendering the Print, rendering of a scene referred image is largely concerned with mapping the extended luminance of a scene to the limited dynamic range of the output medium. This may be accomplished to some extent with sigmoidal tone curve, but more sophisticated techniques are needed for HDR images. Color may also need to be remapped, but to a much lesser degree if one is using wide gamut displays and printers. With color, the saturation is often adjusted, but hue changes are not generally desired. If we had a display capable of high dynamic range and with a large color gamut, the scene referred image with proper white balance would reproduce the scene. Viewing conditions of the image are also important and are taken into account by CIECAM02 (http://en.wikipedia.org/wiki/CIECAM02). With most existing output devices, scene referred data is not pleasing, and rendering into an output space is performed. The thrust of my quest for accuracy is to obtain an accurate scene referred raw file. From there, one may make further adjustments to achieve the desired effect.
And while I disagree with the idea that an 'accuate' WB is the best way to achieve a proper scene-referred image and that a camera profile, similarly, is the Holy Grail I reference this from "Real World Color Management, 2nd Ed" by Fraser, Murphy & Bunting: "Camerra profiles are a bit more slippery. We've found that even with the best camera profiles, we'll still have to make significant edits to tone, and when camera metamerism rears its head, to color too." Further, the authors continue to state that a good camera profile is merely a 'nudge in the right direction'.
I think that Fraser et al were referring to making ICC profiles for cameras. These are generally valid only under standardized environments such as in the studio or laboratory where the illuminant can be controlled. In all cases, some type of profile is needed to convert the XYZ values produced by the camera to the working space such as ProPhotoRGB. A 3x3 matrix is generally used, and further modifications with look up tables may be involved as with the DNG profiler. Some insight into how this is done in Adobe applications can be gained by studying the source code of the DNG SDK.
Regards,
Bill
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Answer the question that was put to you: Given your strong preference for 'colorimetric accuracy', how did you ever operate in the world of film photography?
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Answer the question that was put to you: Given your strong preference for 'colorimetric accuracy', how did you ever operate in the world of film photography?
Funny that you should make such a request for me merely to answer your question (which was off topic and irrelevant to the discussion, but presumably designed to trip me up), since I've been asking the same from you with no success, even for relevant questions.
Much of my film work was with black and white, so colorimetric accuracy was not relevant, but one might put a yellow filter over the lens.
Most of my color work was with chromes, and Kodachrome 25 was my long time favorite. Variations in processing were out of the question with this film and you had to get exposure and color balance correct in camera. Of course, white balance was critical. For tungsten (3200K), an 80A filter could be used. For minor corrections warming filters could be employed, but I never tried CC filters. At that time my knowledge of colorimetry was meager and of limited importance to me since I could not evaluate color except by eye and I couldn't control it other than to use proper technique. I occasionally used pre-flashing to reduce contrast.
For photo-microscopy, we often used Ektachrome EPY with a one stop push to increase contrast. When Velvia came out, that was my favorite film for photo-microscopy and landscape because of its saturated colors. Velvia was not good for portraits with Caucasian skin, and Kodachrome or Astia was better for portraits. Kodak always sought to produce accurate colors and their films fell out of favor with some who preferred the increased saturation of the newer films. As you and others have noted, pleasing color is often preferable to accurate color. It depends on what one is trying to achieve. Generally, one often wants more saturation, but hue shifts are usually undesirable. With digital, increased saturation is easily accomplished in post, but is is more difficult to correct hue shifts. That is why Imatest reports color difference with and without correction for chroma (saturation).
Now, I invite you to answer my questions on what is wrong with my evaluation of color accuracy using Imatest rather than saying it is flawed and irrelevant. I won't hold my breath while awaiting your answer.
Regards,
Bill
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Because of colorimetric matching limitations, or rather because of currently actual trend & fashion in photography?
Simply preference (like film).
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Now, I invite you to answer my questions on what is wrong with my evaluation of color accuracy using Imatest rather than saying it is flawed and irrelevant. I won't hold my breath while awaiting your answer.
Regards,
Bill
You never mentioned Imatest until a few posts ago in this thread. You've not indicated it's a part of your workflow. You've indicated that an 'accurate' white balance is what's required for colorimetric accuracy. That's what I and others dispute. And you didn't answer the question I put to you. You typed a lot but didn't answer the question. In point of fact you confirmed what Andrew, Tim and others have alluded to all along. Done. Finished.
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The advantage I can see in the ColorRight diffuser over the grey card is that you operate it on the camera, or at arms length. The card requires to be placed in the distance of focus. Otherwise, the same considerations apply.
Yes, it's a Through-the-Lens device. The central portion diffuses the light entering the camera lens (ie, placed so it temporarily replaces where the plastic lens protector would normally be), switch auto-focus off and then set the white balance on the camera itself (I have a handy button that speeds this process up considerably without needing to switch auto-focus off). If used as a grey card it merely needs to be in the scene with enough pixels to evaluate your own white balance, not necessarily with accurate focus. There's the ColorRight Pro (and Pro Max) which apparently has better transmissive capability with a dome design to capture light from multiple angles however I find it fairly bulky (though probably not too bad for DSLR owners).
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You never mentioned Imatest until a few posts ago in this thread. You've not indicated it's a part of your workflow. You've indicated that an 'accurate' white balance is what's required for colorimetric accuracy. That's what I and others dispute. And you didn't answer the question I put to you. You typed a lot but didn't answer the question. In point of fact you confirmed what Andrew, Tim and others have alluded to all along. Done. Finished.
... if I photograph an X-Rite color checker and render it into a defined color space such as ProPhotoRGB, I can compare the observed values in the file to those measured from the target by a laboratory grade spectrophotometer and determine the accuracy of the rendering and give a mathematical analysis. For more practical work, one could assume that the color checker is reasonably accurate. It helps to know the white balance for the illumination used to take the photograph. What is subjective about this?
Bob,
Not only are you very thin skinned and argumentative, but your reading comprehension and ability to draw conclusions from the text is limited. My initial post in reply to the DigitalDog's comment about accuracy is quoted above. All Imatest ColorCheck does is to compare the values of the rendered image to the nominal values of the ColorChecker and perform related calculations. White balance is necessary for this process. I later invoked Imatest to indicate that Normal Koren, the author of Imatest, thought that this methodology was sound.
Since you misinterpret what I said and won't respond to my questions and assertions and a meaningful discussion is not possible, I agree that continuing this thread is pointless. I have looked at your website and read some of your posts and conclude that you are knowledgeable, but I don't know why do you have to prove that you know more than others? You need to read this book (http://www.amazon.com/Im-OK-Youre-OK-Thomas-Harris/dp/038000772X).
Regards,
Bill