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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 228726 times)

Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #360 on: January 06, 2011, 10:31:39 am »

Look along the axis.

Which one?  Why don't you just say what you think is wrong and stop the guessing game.
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Peter_DL

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #361 on: January 06, 2011, 11:47:15 am »

Isn't that the same as when I said to use Prophoto RGB (D65) instead of standardized Prophoto RGB (D50), ... ?

No, scene white: D65 is white-balanced and mapped (on)to regular ProPhoto RGB D50 white, which corresponds to a RelCol transform. By purpose I left out all such hybrid spaces as ProPhoto RGB D65 with my considerations as given above in reply #355. However, we could include it if you feel it’s decisive. Also, by purpose I did not presume any limitations regarding the colors being present in the scene, inside or outside the house.

At the and of the day it is one thing to provide evidence for a specific effect, to calculate it, to illustrate it with 2D or 3D plots, or in Photoshop (as I did: Adobe RGB white to blue being abscol outside ProPhoto RGB). It’s however another thing to work out where it really matters along the digital imaging processing chain. So far my conclusion is that it finally does not matter, because it does not seem to be possible to freeze the abscol differences between Adobe RGB and ProPhoto RGB.

Sincerely,
Peter

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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #362 on: January 06, 2011, 12:55:47 pm »


No, scene white: D65 is white-balanced and mapped (on)to regular ProPhoto RGB D50 white, which corresponds to a RelCol transform. By purpose I left out all such hybrid spaces as ProPhoto RGB D65 with my considerations as given above in reply #355. However, we could include it if you feel it’s decisive. Also, by purpose I did not presume any limitations regarding the colors being present in the scene, inside or outside the house.

At the and of the day it is one thing to provide evidence for a specific effect, to calculate it, to illustrate it with 2D or 3D plots, or in Photoshop (as I did: Adobe RGB white to blue being abscol outside ProPhoto RGB). It’s however another thing to work out where it really matters along the digital imaging processing chain. So far my conclusion is that it finally does not matter, because it does not seem to be possible to freeze the abscol differences between Adobe RGB and ProPhoto RGB.

Sincerely,
Peter

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Oh I see what you are saying.

In this particular case of Adobe RGB (D65) and Prophoto RGB (D50) the contentious colors were a segment from saturated blues to white. As Iliah also pointed out that depending upon other spaces and different source and target white points the gamut mismatch can happen in other parts of the spectrum.

So is your conclusion only specific for Adobe RGB (D65)->Prohoto RGB (D50) or it applies as a general case with color management?

Sincerely,

Joofa
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Peter_DL

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #363 on: January 06, 2011, 03:06:29 pm »

In this particular case of Adobe RGB (D65) and Prophoto RGB (D50) the contentious colors were a segment from saturated blues to white. As Iliah also pointed out that depending upon other spaces and different source and target white points the gamut mismatch can happen in other parts of the spectrum.
So is your conclusion only specific for Adobe RGB (D65)->Prohoto RGB (D50) or it applies as a general case with color management?

Joofa, - honestly I don’t understand what you mean. My conclusion is "absolute", however, please feel invited to break open these considerations as given in reply # 355, or to provide a different train of thoughts. But please no single lines on "multispectral imaging in a narrow bandwidth" or pointing to 3D gamut plots. I’ll be all open for any fully developed thread along the imaging processing chain about the relevance of Abobe RGB hues being abscol outside ProPhoto RGB.

Sincerely,
Peter

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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #364 on: January 06, 2011, 03:25:43 pm »

Joofa, - honestly I don’t understand what you mean. My conclusion is "absolute", however, please feel invited to break open these considerations as given in reply # 355, or to provide a different train of thoughts. But please no single lines on "multispectral imaging in a narrow bandwidth" or pointing to 3D gamut plots. I’ll be all open for any fully developed thread along the imaging processing chain about the relevance of Abobe RGB hues being abscol outside ProPhoto RGB.

Sincerely,
Peter

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Hi Peter,

I get your point. I want to thank you for being so understanding of some of the stuff I was trying to say. One of my weaknesses, which I have identified before also, is that while I can understand stuff in color theoretic models, I don't fully understand the workflows of professional photography, and especially when it comes to color management through the "usual" stuff.

I shall think more about the issues raised in this thread and if I have anything useful to say then I shall share it.

But thanks again for all the help.

Best regards,

Joofa
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Stephan Jones

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #365 on: January 06, 2011, 04:01:23 pm »

I had a similar discussion with my ex about France's lack of horses. She doesn't really talk to me anymore, but I don't think she'd mind if I paraphrased an old conversation:

ME: I wonder what the French did before modern transportation without horses. The word 'horse' isn't even in their vocabulary. How did they get around?

SALLY: Huh? They do have a word for horse; it's 'cheval'

ME: Nope. That's not what I'm talking about. I'm talking about 'horse' in an absolute sense. I don't care about 'cheval.' They're not even the same word.

SALLY: I'm talking about the idea. 'Cheval' in French points to the same idea that 'horse' points to in English. 'Horse' is just a word, you can't ride a word.

ME: Well, you can't ride an idea either, what's your point? [Sally could be a little dense and stubborn, which explains why she is the ex, I think].

Now that I've read and understood this thread. I wish I could go back to that warm summer day with Sally. I'd have the perfect retort:
'Horse' is out of the gamut of the French language. I'd like to see her put that in her pipe and smoke it.

Now that I'm on firm scientific ground about this, I'm going to see what important and practical conclusions I can draw from this revelation. Thanks for the help Joofa!
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #366 on: January 06, 2011, 04:19:16 pm »

I had a similar discussion with my ex about France's lack of horses. She doesn't really talk to me anymore, but I don't think she'd mind if I paraphrased an old conversation:

[SNIPPED]

Now that I'm on firm scientific ground about this, I'm going to see what important and practical conclusions I can draw from this revelation. Thanks for the help Joofa!

Stephen, it is not difficult to understand. Lets take your example of distance to your office. You woke up the first day of your job and left your house, traveled northbound, without turning arrived at your office. You looked at your odometer and distance was 15 KM. Sally calls you. Just checking if you are nervous about your first day. But you seem fine. You looked at the sky. It seemed the weather was going to change soon.  But, it was your first day of job, so you had to get in the office.

Before we go on any further a little about the meaning of the notion of distance. 1 KM = 1000 meters. Right? Lets not further divide the meter into cms, mm, etc., and say our "unit vector" is 1m. But how long is one 1m  ??? ??? ??? Your odometer has some idea of how long it should be and you trusted it when it told you the distance was 15 KM.

In the evening you wanted to get back home. It was all dark, cloudy, raining cats and dogs, and snowing. You could not see past a short distance. You thought that your office and house were on a straight road and you traveled northbound in the morning 15 KM so you shall go southbound 15 KM and reach home by just paying attention to the odometer. However, meanwhile your odometer had a mind of its own and it changed the notion of how long is a 1m, and it increased its original notion of 1m by some margin, and started thinking that this is the "new" 1m. But you just went blindly by 15KM, so when the odometer told you it is 15KM you looked around but you were not at your home. You were in a dark place with howling wolves around. There is no home, no Sally, no nothing. You got terrified, scared, shaking in boots, closed your eyes, and sincerely prayed that you will never disagree with Joofa again if you get another chance at life. There was a flash in sky, a strange light. You opened your eyes. You were in your bed. The date was your first day of work. You left home, and reached the job, and incidently noted the distance on your odometer. It was 15 KM. You looked at the sky. It was a shining day. Sally calls you. You say you are doing fine. You looked at your office building, and then reached in to your bag in the car, flipped out your digital camera, and thought who cares if it is a first day. Lets snap some pictures.

Sincerely,

Joofa
« Last Edit: January 06, 2011, 05:41:27 pm by joofa »
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Stephan Jones

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #367 on: January 06, 2011, 06:05:57 pm »

Of course I'm toying with you Joofa, but you're a real champ to play along.

I'm not a photographer, but a friend pointed this thread out and thought I'd enjoy it. And I did. I work in color: I started out working in industrial pigment doping and now I do advanced detection which involves some color modeling. I say that not to impress, but to encourage you to lower your defenses a bit and really understand the disagreement here. It's actually a common disagreement that generally happens when both sides are only willing to understand their half of the problem. It often boils down to photometry vs colorimetry vs. radiometry vs. appearance modeling. Google will be your best friend here.

Basically, Joofa, you are giving too much credit to the CIE XYZ model when it comes to color. Honesty, it's a little comical because you also criticize it at the same time. Now, I use the word color very specifically to mean the interaction between the human visual system, a light source, and an object. You'll hear this called the color triangle in the literature. Because the CIE model has very specific restraints, one gets into all manner of trouble if one tries to replace the human in the triangle with the CIE model. At it's heart, as someone above pointed out, the CIE model only deals with color matching under the same conditions. Again, it's not a model of color, it models color matching—that's a very important distinction. There's a reason the spectral tristimulus values at the heart of the CIE system are called color matching functions. They are not color defining functions.

It really is useful to talk about absolute colors. But an XYZ tristimulus value is only a color in the same sense that a spectral power distribution is a color. They are both absolute in their own sense, you are totally right about that, but when you speak of them this way you remove the human from the color triangle and so you are no longer really talking about color.

These days, we find it much more useful to talk about fundamental tristimulus values which are based on cone responses rather than 100 year-old color matching data. Believe me, if the CIE had direct cone response data, they would have used it instead of the color matching function. A stimulus that provides the same cone response can (with a lot of caveats) be called the same color. The RLAB space does this and it's not really hard to understand, but the first thing you will notice when you try to go from XYZ to RLAB is a chromatic adaptation matrix, which you seem to really dislike for some reason. The CIECAM02 model requires the same thing (this is instructive: http://www.polybytes.com/misc/Meet_CIECAM02.pdf but again chromatic adaptation is front and center). All color appearance models need to account for chromatic adaptation because it's a fact of the human visual system and the human visual system is central to any conversation about color.

So now look at your problem from this perspective. Take your blue primary in the Adobe color space and, instead of jumping right into the CIE XYZ model, try to think in terms of cone response. If you do that then you'll be beginning to talk about color rather than a matching model or an old photometric definition. If you'll go that far with me, you'll see that you can in fact produce that same cone response with the ProPhoto space. Which is to say, the color is available in ProPhoto. That isn't to say your facts are wrong, just that they aren't as applicable to color (by mine and most everyone's definition) as you assert.

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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #368 on: January 06, 2011, 06:26:00 pm »

I'm not a photographer, but a friend pointed this thread out and thought I'd enjoy it. And I did.

I’m sure glad he did, welcome!

Quote
At it's heart, as someone above pointed out, the CIE model only deals with color matching under the same conditions. Again, it's not a model of color, it models color matching—that's a very important distinction. There's a reason the spectral tristimulus values at the heart of the CIE system are called color matching functions. They are not color defining functions.

It really is useful to talk about absolute colors. But an XYZ tristimulus value is only a color in the same sense that a spectral power distribution is a color. They are both absolute in their own sense, you are totally right about that, but when you speak of them this way you remove the human from the color triangle and so you are no longer really talking about color.

These days, we find it much more useful to talk about fundamental tristimulus values which are based on cone responses rather than 100 year-old color matching data. Believe me, if the CIE had direct cone response data, they would have used it instead of the color matching function. A stimulus that provides the same cone response can (with a lot of caveats) be called the same color. The RLAB space does this and it's not really hard to understand, but the first thing you will notice when you try to go from XYZ to RLAB is a chromatic adaptation matrix, which you seem to really dislike for some reason. The CIECAM02 model requires the same thing (this is instructive: http://www.polybytes.com/misc/Meet_CIECAM02.pdf but again chromatic adaptation is front and center). All color appearance models need to account for chromatic adaptation because it's a fact of the human visual system and the human visual system is central to any conversation about color.

So now look at your problem from this perspective. Take your blue primary in the Adobe color space and, instead of jumping right into the CIE XYZ model, try to think in terms of cone response. If you do that then you'll be beginning to talk about color rather than a matching model or an old photometric definition. If you'll go that far with me, you'll see that you can in fact produce that same cone response with the ProPhoto space. Which is to say, the color is available in ProPhoto. That isn't to say your facts are wrong, just that they aren't as applicable to color (by mine and most everyone's definition) as you assert.

Wow, great post. We really need a volunteer to put all the salient points together into some kind of article for LuLa. While this topic kept going and going, and some of it was OT or nasty, there’s some really great discussions and analogies here. I guess I owe Joofa thanks for bringing this group together and for the results it produced. Just needs some editing.
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #369 on: January 06, 2011, 06:34:23 pm »


These days, we find it much more useful to talk about fundamental tristimulus values which are based on cone responses rather than 100 year-old color matching data. Believe me, if the CIE had direct cone response data, they would have used it instead of the color matching function. A stimulus that provides the same cone response can (with a lot of caveats) be called the same color.

That has me quite puzzled.  I would have thought that all the above discussion about chromatic adaptation would tell us that a given cone response can yield a different color perception depending on the context.   Such as the checkerboard 'optical illusion' earlier in the thread (forgive me for not wading through all 19 pages to find it).
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emil

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #370 on: January 06, 2011, 06:35:48 pm »

Stephen,

Firstly, you have not realized that what ever I was saying had chromatic adaptation built right into it - in a way that it will automatically happen, when it was indeed needed. You may not have realized it. And, for that I would encourage you to read my messages again and study my plots more closely.

And, it might appear to you that I am giving to much credit to XYZ, but that is not the case at all. I don't think you have realized why I used the word canonical in relation to it. I will go back to my notion of "how long is 1m"? You need to establish a "yardstick" from which to measure. XYZ, RGB, linear LMS (human vision), or any other linear derivative spaces are no special in this regard. But we have to pick one and use it as a yardstick. And, you may not have realized it, but in calorimetry, the canonical yardstick for measurement is XYZ. That is why there is only a single notion of white point [1,1,1] in XYZ, while other spaces, which are schematically the same, share the same space with XYZ, are allowed to have varying notion of white point. I cannot overemphasize this fact. There is no need to go into models of perception, and chromatic adaption, unless you have realized this basic fact.

If you think that by pointing out the "absoluteness" of XYZ, I am ignoring chromatic adaption, you were not paying attention to my messages.

And, now I would request you to kindly write me a matrix for converting CIE RGB->CIE XYZ?

Thanks,

Joofa
« Last Edit: January 07, 2011, 01:10:50 am by joofa »
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #371 on: January 06, 2011, 06:38:44 pm »

> Take your blue primary in the Adobe color space and, instead of jumping right into the CIE XYZ model, try to think in terms of cone response.

Now does the record of colour in a raw file follow cone response?

> we find it much more useful to talk about fundamental tristimulus values which are based on cone responses rather than 100 year-old color matching data

Munsell un-edited experimental data is based on human perception. Does it support your statement?
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #372 on: January 06, 2011, 07:11:13 pm »

That has me quite puzzled.  I would have thought that all the above discussion about chromatic adaptation would tell us that a given cone response can yield a different color perception depending on the context.   Such as the checkerboard 'optical illusion' earlier in the thread (forgive me for not wading through all 19 pages to find it).

Dammit—just when I think I'm done with this thread, it gets interesting again.

Emil, I'm totally guessing, but I think this is part of what goes under "a lot of caveats" in Stephen's post.

Chromatic adaptation that you see in color models is generally correcting for sensory adaptation not cognitive adaptation, which is less well understood. Sensory adaptation happens in the retina, in fact each eye adapts independently (It's the basis of haploscopic testing). You can experiment with this yourself if you have some old school 3D glass. Wear them for a while and when you take them off you'll notice the weird sensation for a few seconds as each each eye readapts back to normal light.

I don't think anybody believes color appearance models have even scratched the surface of the cognitive aspects of color, but I think most people think getting the sensory aspects worked out, even a little, is a giant step.

For a REALLY powerful illusions that demonstrates the cognitive aspect of color, check this out: http://www.lottolab.org/illusiondemos/Demo%2014.html

Also Joofa: Hilbert Space? Seriously? Why stop there? If you really want to set up a smoke screen, you should invoke Zariski–Riemann space.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #373 on: January 06, 2011, 07:16:24 pm »

Also Joofa: Hilbert Space? Seriously? Why stop there? If you really want to set up a smoke screen, you should invoke Zariski–Riemann space.

Smoke screen. Ha ha ha. :D Only if you paid more attention to my comment than being sarcastic.

But seriously, I don't know how to interpret you? Previously I presented a plot so that others can see what I was thinking. And, you came up with a macho statement that you can also produce plots. Now in my respone to somebody else you come up with another mathematical construct. Are you in some sort of competition with me?

Sincerely,

Joofa
« Last Edit: January 09, 2011, 08:26:00 am by joofa »
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #374 on: January 06, 2011, 08:42:39 pm »

For a REALLY powerful illusions that demonstrates the cognitive aspect of color, check this out: http://www.lottolab.org/illusiondemos/Demo%2014.html
this one is also pretty surprising as it does not involve a 3D and shadow effect (move mouse over image):
http://www.richard-ebv.de/images/HDS/test/farbe_macht_abhaengig.html
when you move away from the monitor it's even more surprising.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #375 on: January 07, 2011, 01:46:19 am »

I noticed there is an article on Prophot RGB on this forum with contribution from Bruce Fraser and Jeff Schewe:

http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml

Joofa
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Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #376 on: January 07, 2011, 07:02:24 am »

I noticed there is an article on Prophot RGB on this forum with contribution from Bruce Fraser and Jeff Schewe:
http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtm

They gave feedback and suggestions.  "Contribution" usually means that their writings appear in the article.  For example, you have contributed to this discussion...

That is why there is only a single notion of white point [1,1,1] in XYZ…

Of course, with a tiny bit of research you would have found that the XYZ “white point” (more like the XYZ white) is 1/3, 1/3, 1/3.  Obviously, making a contribution doesn’t attest to the quality of that contribution.

Here’s another contribution...in reference to use of the Bruce Lindbloom calculator...
I think you selected the D50 white point for Adobe RGB, where as the standard says to use D65.

Except that you can’t select a different white point for Adobe RGB...there is no function for that in the Bruce calculator.  The box labeled “Ref White” is for selecting the Standard Illuminant for the CIE spaces, as described in Bruce’s help...NOT for selecting a different white point for the chosen RGB space.  You were using the calculator incorrectly.

And once again we see that making a contribution isn’t always a good thing.

« Last Edit: January 07, 2011, 07:09:01 am by Graystar »
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #377 on: January 07, 2011, 08:23:37 am »

> Of course, with a tiny bit of research you would have found that the XYZ “white point” (more like the XYZ white) is 1/3, 1/3, 1/3.  Obviously, making a contribution doesn’t attest to the quality of that contribution.

Aren't you are mixing up xyz and XYZ?
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Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #378 on: January 07, 2011, 09:06:29 am »

> Of course, with a tiny bit of research you would have found that the XYZ “white point” (more like the XYZ white) is 1/3, 1/3, 1/3.  Obviously, making a contribution doesn’t attest to the quality of that contribution.

Aren't you are mixing up xyz and XYZ?

I was using "XYZ" as "CIE XYZ", the name of the space, in the manner that joofa did in the post I was responding to.  Clearly, improper use of terms, from straight misuse to attempts to match usage, has been a problem in this discussion.

But otherwise, yes of course it's xyz as is stated in any description of the CIE XYZ space.
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #379 on: January 07, 2011, 09:10:41 am »

I was using "XYZ" as "CIE XYZ", the name of the space, in the manner that joofa did in the post I was responding to.  Clearly, improper use of terms, from straight misuse to attempts to match usage, has been a problem in this discussion.

But otherwise, yes of course it's xyz as is stated in any description of the CIE XYZ space.

So, what is the value for white point in XYZ again?
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