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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 222081 times)

jc1

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #160 on: January 04, 2011, 05:27:31 am »

jc1, you did a  nice job on the the graphs, they're cool looking. The conclusion you draw suffers from the same problem Joofa has been having the whole time, though. If I understand what you've done, you are drawing conclusions about points on the same XYZ plot representing two different viewing conditions.

To MarkM,
Thank you for your times. It's a good learning experience.
Yes, the comparison under different illuminants/viewing conditions is meaningless.

regards,
jc1
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #161 on: January 04, 2011, 07:39:08 am »

> the comparison under different illuminants/viewing conditions is meaningless.

It is not, depending on what one is trying to achieve. Is it so difficult to realize that full chromatic adaptation is not something a photographer always needs? Or that chromatic adaption methods in use are often based on pretty rough models?
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jc1

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #162 on: January 04, 2011, 08:43:09 am »

It is not, depending on what one is trying to achieve. Is it so difficult to realize that full chromatic adaptation is not something a photographer always needs? Or that chromatic adaption methods in use are often based on pretty rough models?
Comparison of gamut plots is meaningful unless they are under same viewing conditions. Hope we are on same frequency.

Practically, if 2 similar objects are illuminated each with light source of different colors, it doesn't make sense to compute or compare their color differences. Most of the mathematically functions in color science are well defined and established. An interesting subject. I'm from a different discipline.
 
regards.
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #163 on: January 04, 2011, 09:21:21 am »

If only those mathematical functions you are referring to always surve the purpose and serve it well. Colour science is not "frozen". Fairchild, anybody?
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #164 on: January 04, 2011, 10:10:12 am »

To MarkM,
Thank you for your times. It's a good learning experience.

Ditto! A beautifully well composed, clear explanation. A keeper.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #165 on: January 04, 2011, 10:11:35 am »

Comparison of gamut plots is meaningful unless they are under same viewing conditions. Hope we are on same frequency.

Practically, if 2 similar objects are illuminated each with light source of different colors, it doesn't make sense to compute or compare their color differences. Most of the mathematically functions in color science are well defined and established. An interesting subject. I'm from a different discipline.
 
regards.

Nope, not at all.  Consider this. I take a 100% reflective surface and shine D65 on it measure its XYZ, call it A, and then I shine D50 on it measure its XYZ, and call it B. And A is not the same as B! These two different sets of XYZ are related by a color adaption model say, Bradford, but that is all it is about. Now suppose I decide to measure A and B in a system which has Adobe RGB primaries. I have selected my primaries (chromacity coordinates). However, there is still a very important step here that MarkM is not realizing. While I have picked my primaries I have not defined that while measuring A and B which what is my white point. I have two natural choices, either pick D65 or D50, or  I can even pick a third unrelated color. But we shall only concentrate on the first two. Adobe RGB (D65) is set to produce a tristimulus value of [1,1,1] for A, but something else for B. What MarkM seems unappreciative of the fact is that when he throws in the Bradford transformation it internally restructures the Adobe coordinate system, so that Adobe RGBs are now set to produce the tristimulus [1,1,1] for B, effectively becoming Adobe RGB (D50). At this stage he forgets about color A, which still exists. And if we measure A in the new system then it will be out of gamut.

Hope that helps.

Sincerely,

Joofa
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #166 on: January 04, 2011, 10:44:36 am »

Ditto! A beautifully well composed, clear explanation. A keeper.

+1


@joofa: I suspect Mark understands perfectly well, but prefers to concentrate on the fact that what is relevant for rendering is the color space adapted to the illuminant under which the image was captured.  I suspect from the answer given above to my question, that ACR's adjusting of the 3x3 matrix according to color temp is implicitly jiggering the gamut boundaries to contain the relevant set of colors for the measured illuminant.  The only way I can see comparing colors under different illuminants to be relevant, is if the scene captured has multiple illuminants (eg, Mark's window example).  Then without special treatment, one has to choose an overall illuminant for the scene and its associated adapted gamut, and colors from the other illuminant in the scene might fall outside that gamut even though they can be within the gamut adapted to that other illuminant.
« Last Edit: January 04, 2011, 10:55:10 am by ejmartin »
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emil

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #167 on: January 04, 2011, 11:26:21 am »

The only way I can see comparing colors under different illuminants to be relevant, is if the scene captured has multiple illuminants (eg, Mark's window example).  Then without special treatment, one has to choose an overall illuminant for the scene and its associated adapted gamut, and colors from the other illuminant in the scene might fall outside that gamut even though they can be within the gamut adapted to that other illuminant.

Emil, thank you for saying that. Isn't that point of whole exercise that legal colors within a gamut get mapped to out of gamut in another system? Please think about it.

Joofa
« Last Edit: January 04, 2011, 02:10:44 pm by joofa »
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #168 on: January 04, 2011, 12:08:16 pm »

Hi joofa,

But ...just to clear my stand.
MarkM has made his point loud and clear which I am aware and agree with.  8)

CIE XYZ space only guarantees that colors with the same coordinates will match when viewed under the same conditions. When you plot various XYZ values in that space taken under different assumptions, like illuminant, you can't expect to be able to compare them. Plotting them on the same graph becomes meaningless.  

regards,
jc1

Nope, it is not meaningless. MarkM seems unappreciative of the fact there is not a single XYZ coordinate system in this scenario. There are three in the same 3D space! One is the canonical XYZ system whose "unit vector" length is fixed (what I have been "harping" (Emil's word from a distant time  ;D) all along and seems to be unacknowledged). The other two are, say Adobe RGB primaries adjusted for (1) white point being D65, and (2) white point being D50. Now you are moving between these three different coordinate systems in the same space.

MarkM takes the simplistic view that two points that are different on XYZ coordinate system can't be meaningfully realized on the same plot since they were derived from two different white points. That is why I provided the 3D plot of CIE XYZ and RGB in relative relationship to each other to help illustrate what is going on here.

Joofa
« Last Edit: January 04, 2011, 12:11:07 pm by joofa »
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #169 on: January 04, 2011, 01:00:34 pm »

How it all came to the discussion of inertial frame of reference?
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #170 on: January 04, 2011, 02:17:35 pm »

How it all came to the discussion of inertial frame of reference?

Hi,

If your comment is directed to me then here is my understanding. Assuming linearity of transformations, including chromatic adaption as exemplified by using a linear Bradford matrix, the mechanics of the movement between three coordinate axis in the same 3D space, which I mentioned above, are approximately described by the Bradford transformation.

Sincerely,

Joofa
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #171 on: January 04, 2011, 02:21:56 pm »

Emil, isn't that point of whole exercise that legal colors within a gamut get mapped to out of gamut in another system. Please think about it.

Joofa

There are several points:

1) A color space A is defined wrt a particular illuminant I.  The gamut of allowed colors in that color space (call it G(A,I)) and implicitly referred to that illuminant, is a paralellepiped in XYZ space, three of whose corners are the R,G,B primaries for that color space.
2) Chromatic adaptation maps the parallelepiped of colors in the gamut defined for the reference illuminant, to another parallelepiped G(A',I') of colors referred to another illuminant I'. There are adapted primaries R',G',B'.
3) The adaptation map can be such that the XYZ coordinates of eg the blue primary of A lie outside the parallelepiped G(A',I'). We note this fact and continue.
4) The color 'white' does not have unique XYZ coordinates; it depends on the illuminant, W=W(I).  Part of the map G(A,I)->G(A',I') is W(I)->W(I').  W(I) can also lie outside G(A',I').
5) A second color space B' might be defined wrt a different illuminant I', and determine a gamut parallelepiped G(B',I').  
6) If we are to discuss a given image being formed by a particular illuminant I", each pixel should have a set of X,Y,Z coordinates determined by the spectral power distribution (SPD) of the illuminant and the surface reflectivities of the objects in the scene.  
7) Then to compare the recording of that image in different color spaces A and B', we should be looking at the coordinatization of the colors represented by X,Y,Z as linear combinations of the respective primaries adapted to I" and which may or may not lie within G(A",I") and/or G(B",I").  One can if one wishes then transform the XYZ values to ones determined in the reference color spaces G(A,I) and/or G(B',I') by inverting the chromatic adaptation transform.
8 ) If a viewer wishes to render the image, to be viewed under yet another illuminant I''', then the XYZ values should be mapped by chromatic adaptation to that illuminant.  I'''=I and I'''=I' are special cases.
9) There is no point in the above discussion of points (6-8) where it is necessary to discuss either point (3), or whether eg the blue primary of G(A,I) lies outside G(B',I').  The only issue of possible relevance is whether it lies outside of G(B,I).  In the case of AdobeRGB and Prophoto, the answer is no, the blue primary of Adobe, properly adapted to the illuminant, lies within Prophoto.  This is why I commented that it was a purely theoretical question, without practical import.

At least, this is my current understanding.  I am happy to be further illuminated ;) by the experts.
« Last Edit: January 04, 2011, 04:39:09 pm by ejmartin »
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emil

joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #172 on: January 04, 2011, 02:40:40 pm »

There are several points:

Emil, it appears now you are backtracking from your previous comment that "colors from the other illuminant in the scene might fall outside that gamut even though they can be within the gamut adapted to that other illuminant."  :D

[snipped a lot of stuff as I got lost. Sorry]

Quote
In the case of AdobeRGB and Prophoto, the answer is no, the blue primary of Adobe, properly adapted to the illuminant, lies within Prophoto.  This is why I commented that it was a purely theoretical question, without practical import.

Your "blue primary of Adobe, properly adapted to the illuminant" is what I have been calling the blue primary of Adobe RGB (D50). If you go to the back of this thread and start reading my messages again you will see that I have said that blue primary of Adobe RGB (D50) is contained within Prophoto RGB (D50), this is my case (3) presented below, which is copied from the very first note I wrote on this topic, but not the blue primary of Adobe RGB (D65), my case (1) below. Why don't you realize that the issue is the representation of blue primary of Adobe RGB (D65), which is a valid color in its measurement system, to the measurement system of Prophoto RGB (D50)? And, again, please don't let chromatic adaption confuse you.

Iliah Borg has also demonstrated that using Bruce Lindbloom's calculator.

Quote
Joofa wrote on DPReview:

Fraction of unit stimulus blue ProPhoto RGB primary needed to match unit stimulus blue Adobe RGB primary:

(1) Adobe RGB white point=D65, PropPhoto RGB white point=D50, Fraction needed=1.2

(2) Adobe RGB white point=D65, PropPhoto RGB white point=D65, Fraction needed=0.91

(3) Adobe RGB white point=D50, PropPhoto RGB white point=D50, Fraction needed=0.88

(4) Adobe RGB white point=D50, PropPhoto RGB white point=D65, Fraction needed=0.67

You can choose to say what is of practical significance or not. But that has no relevance to this discussion.

Sincerely,

Joofa
« Last Edit: January 04, 2011, 02:46:17 pm by joofa »
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #173 on: January 04, 2011, 02:53:34 pm »

Emil, it appears now you are backtracking from your previous comment that "colors from the other illuminant in the scene might fall outside that gamut even though they can be within the gamut adapted to that other illuminant."  :D


Not at all.  If the dominant scene illuminant is I and we record it as a set of RGB values wrt a color space adapted to it, G(A,I) (even though the definition of that color space may refer to some other illuminant), then a set of XYZ responses from a second illuminant I' may lie outside of G(A,I).  It may lie outside it even though, had the entire scene been illuminated with I', those responses would lie within G(A',I').
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #174 on: January 04, 2011, 02:54:02 pm »

You can choose to say what is of practical significance or not. But that has no relevance to this discussion.

Maybe you could tell us, based on the usage of the two working spaces, what relevance altering the values to produce a result you wish to illustrate (in terms of the two gamuts) brings to the party. I’ve got the two profiles in question that are used in dozens upon dozens of color managed app’s. Aside from using Bruce’s color calculator to insert a specification to produce the results you want to show us, just what is the practical relevance? Just how or why would I find this of any practical usage with the profiles and products available that utilize these profiles/working spaces/and their gamuts? How or why would I attempt to produce the results your theory presumably illustrates outside of Bruce’s calculator? That’s the $64K question.

Or is this just a theoretical “if a tree falls in the forest” exercise that is long due to finish its course here?

Lastly, the sentence “But that has no relevance to this discussion“ is of course just your opinion. I suspect many here wonder if there is any relevance to a great deal of the discussion this late in the game. Certainly if it has no real world usage. Does it?

Lets not forget the target audience of the LuLa site. You might find your ideas better received on the ColorSync list. Or as mentioned below, do we drag this theoretical verbal diarrhea into the “how many ICC profiles can dance on the head of a pin” debates.
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Peter_DL

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #175 on: January 04, 2011, 02:58:45 pm »

The only way I can see comparing colors under different illuminants to be relevant, is if the scene captured has multiple illuminants (eg, Mark's window example).  Then without special treatment, one has to choose an overall illuminant for the scene and its associated adapted gamut, and colors from the other illuminant in the scene might fall outside that gamut even though they can be within the gamut adapted to that other illuminant.

Another example:
at sunset condition we are chromatically adapted to the extent that we still recognize a white T-shirt as being white. But would we click-balance it in the Raw converter (?). This could certainly help to avoid too saturated red hues in the sky, thus taming the colors inside our working space (whatever it is). However, if the capture is more focused on the landscape rather than the T-shirt, we would probably desist from doing such click-whitebalance - it would most likely destroy the mood of scene i.e. image appearance on screen (unless of course our monitor would be calibrated to an idiosyncratic warm white).

So it seems that chromatic adaptation has its limitations
… as does ProPhoto RGB.

Peter

--
Screenshot of a Granger Rainbow in Adobe RGB
Customized Proof Setup to ProPhoto RGB, AbsCol rendering
Gamut warning enabled, Conversion Engine: Microsoft ICM
Photoshop CS4 on Windows (should work with Apple’s CMM as well, and was also given with Adobe’s ACE in former Photoshop CS).
Corresponds to some of the 3D plots at least which we have seen here...
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #176 on: January 04, 2011, 03:04:10 pm »

Photoshop CS4 on Windows (should work with Apple’s CMM as well, and was also given with Adobe’s ACE in former Photoshop CS).

Try ACE, at least on this end, very different results! The rendering intent (well Perceptual and Saturation don’t exist anyway) make no differences.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #177 on: January 04, 2011, 03:05:37 pm »

Not at all.  If the dominant scene illuminant is I and we record it as a set of RGB values wrt a color space adapted to it, G(A,I) (even though the definition of that color space may refer to some other illuminant), then a set of XYZ responses from a second illuminant I' may lie outside of G(A,I).  It may lie outside it even though, had the entire scene been illuminated with I', those responses would lie within G(A',I').

Emil, please work out my case (1) presented above, as I have done several times on this list, and kindly let me know how do you contain Adobe RGB (D65) primary without more than unity stimulus from blue Prophoto RGB (D50)? And, please don't work out my case (3) above when you think you are working case (1). Please show some numbers.

Sincerely,

Joofa
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #178 on: January 04, 2011, 03:07:08 pm »


Digital dog you are free not to participate. No body is forcing you to. And, please develop a better understanding of the theory of color science.

Joofa
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #179 on: January 04, 2011, 03:22:25 pm »

Try ACE, at least on this end, very different results! The rendering intent (well Perceptual and Saturation don’t exist anyway) make no differences.
verifying clipping with abscol RI is the same trap I fell in some pages above...
ACE doesn't show clipping as it converts recol. If you switch to Apple CMM you'll see the clipping.
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