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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 227674 times)

Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #220 on: January 04, 2011, 07:39:12 pm »

Point is - in a typical scene there are several different white points, with different CCTs and different SPDs.
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #221 on: January 04, 2011, 07:44:45 pm »

Mark I thought we agreed that XYZ=[0.188185   0.075274   0.991108] is outside Adobe RGB (D50) gamut but within Adobe RGB (D65) gamut in absolute terms. I don't know why are you getting confused.

I said nothing about XYZ=[0.188185   0.075274   0.991108]. I am talking about this: XYZ=[0.188185   0.075274   0.991108]  viewed in a D50 environment.

Do you understand the difference?

Do you understand what I mean when I say:
XYZ [0.188185   0.075274   0.991108] viewed in D50 is not the same color as XYZ [0.188185   0.075274   0.991108] viewed in D65?
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #222 on: January 04, 2011, 07:48:10 pm »

Point is - in a typical scene there are several different white points, with different CCTs and different SPDs.
don't know what "CCT" and "SPD" stands for... but why would I care about different white points as long I can store all the colors captured in one color space?
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #223 on: January 04, 2011, 07:51:06 pm »

I said nothing about XYZ=[0.188185   0.075274   0.991108]. I am talking about this: XYZ=[0.188185   0.075274   0.991108]  viewed in a D50 environment.

Do you understand the difference?

Do you understand what I mean when I say:
XYZ [0.188185   0.075274   0.991108] viewed in D50 is not the same color as XYZ [0.188185   0.075274   0.991108] viewed in D65?

XYZ space has only a single notion of white point and that is [1,1,1]. A statement such as "viewing in a D50 or D65 environment" in connection to XYZ is not correct. You can assign D50 and D65 to other RGB-type spaces only. BTW, schematically, there is no difference between XYZ, RGB, linear LMS, or any other linear derivative space. However, if you assign a notion of a white point other than [1,1,1] to XYZ you will mess up the structure of colorimetry.

Joofa
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #224 on: January 04, 2011, 07:53:51 pm »

Correlated Color Temperature and Spectral Power Distribution. Try coming up with a colour space that will capture the gamut of ProPhoto RGB adapted to 3000K and the gamut of ProPhoto RGB adapted to 7500K. Do you think regular ProPhoto can encompass both gamuts?
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #225 on: January 04, 2011, 07:59:34 pm »

Correlated Color Temperature and Spectral Power Distribution.
thanks!

Quote
Try coming up with a colour space that will capture the gamut of ProPhoto RGB adapted to 3000K and the gamut of ProPhoto RGB adapted to 7500K. Do you think regular ProPhoto can encompass both gamuts?
you can create such a color space in Capture One easily. Question is whether or not it is useful... but you can, no problem.

attached the largest color space you can create in Capture One (wireframe | D50, Gamma 1.8 ) compared to "ProPhoto" (shifted to D75 in Photoshop... so another joofa-space just for the purpose of comparision)


« Last Edit: January 04, 2011, 08:10:42 pm by tho_mas »
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #226 on: January 04, 2011, 08:03:30 pm »

Joofa, I understand CIE XYZ space just fine. I normally have a copy of Wyszeck & Stiles in arm's reach.

One last time: I'm not talking about assigning a white point, I'm talking about understanding the viewing conditions—the state of the viewer. Matching XYZ coordinates is only valid under the same viewing conditions. If you are talking about comparing XYZ values in different states of chromatic adaptation (which is what you are doing) your results are meaningless unless you account for it.

I've explained is well as I can in post #159

I'm done here.
« Last Edit: January 04, 2011, 08:05:01 pm by MarkM »
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #227 on: January 04, 2011, 08:07:42 pm »

Joofa, I understand CIE XYZ space just fine. I normally have a copy of Wyszeck & Stiles in arm's reach.

One last time: I'm not talking about assigning a white point, I'm talking about understanding the viewing conditions—the state of the viewer. Matching XYZ coordinates is only valid under the same viewing conditions. If you are talking about comparing XYZ values in different states of chromatic adaptation (which is what you are doing) your results are meaningless unless you account for it.

I've explained is well as I can in post #159

I'm done here.

The problem here is that you are not realizing when you said "viewing XYZ in D65 or D50" you actually want to say viewing the same XYZ coordinates in some RGB (D50)  and RGB (D65) environment. In those two RGB spaces, the same XYZ coordinate can have different representations (tristimulus). And you are not realizing that is the very fact that the same XYZ=[0.188185   0.075274   0.991108] becomes in-gamut in  Adobe RGB (D65) but out-of-gamut in Adobe RGB (D50) in absolute terms.

Joofa
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #228 on: January 04, 2011, 08:15:41 pm »

> you can create such a color space in Capture One easily

How you checked it encompasses both? By running a colour list that contains all the XYZ values from both gamuts?

> Question is whether or not it is useful

Things are useful when one can apply those things, right?
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #229 on: January 04, 2011, 08:19:40 pm »

> you can create such a color space in Capture One easily

How you checked it encompasses both? By running a colour list that contains all the XYZ values from both gamuts?
no, just by looking at Color Think's grapher (admittedly only for the D75 shifted ProPhoto).
edit: but both the color spaces are displayed abscol in relation to D50 BTW ... so the "D75"-ProPhoto is shifted towards blue...  the white points are not equalized.

Quote
> Question is whether or not it is useful
Things are useful when one can apply those things, right?
okay, that's true!
« Last Edit: January 04, 2011, 09:09:32 pm by tho_mas »
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fdisilvestro

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #230 on: January 04, 2011, 09:05:10 pm »

I'm trying to visualize this problem, (from empirical observations, it may not make sense at all, feel free to ignore or disregard)

XYZ space is absolute, is not relative to viewing conditions.

A specific illuminant define a white point vector (be it D50, D65, etc)

Different illuminant vectors or white point vectors are not parallel but angled between each other.

Color spaces are volumes that are not necessarily orthogonal to XYZ, and are associated to a specific white point vector, and with the vector and color space we have a white point coordinate in XYZ

A Viewing condition is similar to position the observer just in line with a white point vector. In this case, any XYZ coordinate along the white point vector is neutral (R=G=B).

If from a viewing condition the observer looks at any point along the white vector of another illuminant, it will perceive non neutral colors (Even if in the color space belonging to the other illuminant R=G=B)

This may be the case if our  viewing condition is  D50, ProphotoRGB, Here R=G=B will look neutral. If from this same position we look at AdobeRGB D65, then the values of adobeRGB R=G=B will not be perceived as neutral

It is like both color spaces where not aligned, and in this case it happens that the blue primary of AdobeRGB is outside of the gamut of ProphotoRGB.

For simplicity and practical purposes, the solution apparently implemented in common color conversion tools is to align both spaces so that the white point vectors are parallel or aligned. I think of this like a "rotation" of one color space to align to the other.

As I understand, the standard practice is to align all color spaces to D50 (It could have been D65 or any other)

When you "rotate" or move a color space (which is my interpretation of Chromatic adapation) some colors that where inside its gamut, are now outside, and vice versa, colors that where outside of the gamut are now inside)

For example, original blue primary of AdobeRGB D65 is now out of gamut in AdobeRGB D50 but it may be the case ( I have not done the calculations) that the new Red primary of AdobeRGB D50 was previously out of the gamut of AdobeRGB D65

Doing conversions from one space to another is now easier, since R=G=B is neutral for both spaces now.

So, if you keep adobeRGB with white point D65, its blue is outside the gamut of ProphotoRGB D50. it is only when you do chromatic adaptation of adobeRGB to D50 that it is completely inside of ProphotoRGB. This is the way that most current applications work and it is the practical way of handling color conversions at present time.

Now, I think that we should discuss about how color management should evolve, how future applications should handle color management instead of arguing if a color in a specific color space is inside or outside of another color space.

Some posters like Iliah have pointed out interesting comments and references about this.

Hope I didn't annoy anybody




MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #231 on: January 04, 2011, 09:46:04 pm »

Francisco, I thought I was done with this thread, but your post provides an interesting way of looking at the problem. It's very satisfying. But, I think one thing that needs to be handled carefully to avoid confusion is the term 'color.' Without including the information about the position of the observer, is it helpful to talk about an XYZ coordinate as a color? It seems like referring to an XYZ point without reference information as a 'color' is a kind of reification error. If you do this, you get into the uncomfortable position of talking about two perceptions which match, but are not the same 'color' or two that don't match that are the same 'color.'

That's important when you want to compare gamuts. For instance, in your example from the perspective of somebody aligned with D50, the XYZ point of the AdobeRGB blue primary falls outside of the ProPhoto gamut (it also falls out of the AdobeRGB gamut from this perspective). But from the same perspective of the D50 viewer there is different XYZ point which matches in perception the original blue primary as seen from D65 and is inside the D50 gamut. So the question becomes is the color indicated by AdobeRGB(0, 0, 255) inside or outside the ProPhoto Gamut. Or to put another way: can a color be specified in the ProPhotoRGB space that matches the color indicated by AdobeRGB(0, 0, 255). The answer of course is yes if you mean by color a perception.

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Schewe

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #232 on: January 04, 2011, 09:54:58 pm »

So, if you keep adobeRGB with white point D65, its blue is outside the gamut of ProphotoRGB D50. it is only when you do chromatic adaptation of adobeRGB to D50 that it is completely inside of ProphotoRGB. This is the way that most current applications work and it is the practical way of handling color conversions at present time.

Correct...nicely stated. So for the purposes of actually DOING anything with different color spaces, all of Adobe RGB color gamut fit's within ProPhoto RGB when you do a color transform...so anything that WAS inside of Adobe RGB (1998) will end up being contained inside of ProPhoto RGB.

So for practical purposes (and anybody who is a glutton for punishment) if you start with a raw digital capture and are using either Camera Raw or Lightroom (the vast majority of the market), processing your images in ProPhoto RGB (which is the largest gamut available in both applications) should not clip any of the colors your camera has captured...and if it does because of some weird spectral illumination that you shot under, it won't matter anyway because you can't get a larger color space inside ACR or LR. However, you "might" be able to control those weird colors if you create a custom DNG profile using something like DNG Profile Editor. This is often needed for cameras whose infrared filters have been removed.

As for postulating on what changes may be needed for the future of color management, I'm game. But I SERIOUSLY suggest starting a whole new thread for that because, well, the vast majority of the readers here on LuLa prolly won't want to wade through clutter in this thread.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #233 on: January 04, 2011, 10:02:53 pm »

Correct...nicely stated. So for the purposes of actually DOING anything with different color spaces, all of Adobe RGB color gamut fit's within ProPhoto RGB when you do a color transform...so anything that WAS inside of Adobe RGB (1998) will end up being contained inside of ProPhoto RGB.

No.
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Joofa
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Schewe

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #234 on: January 04, 2011, 10:08:44 pm »

No.

So, how do you do a color transform from one color space to another (using ICC color space profiles) using a CMM without having the chromatic adaptation applied?
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Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #235 on: January 04, 2011, 10:12:33 pm »

So, how do you do a color transform from one color space to another (using ICC color space profiles) using a CMM without having the chromatic adaptation applied?

Incorrectly. ;)
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #236 on: January 04, 2011, 10:20:18 pm »

So, how do you do a color transform from one color space to another (using ICC color space profiles) using a CMM without having the chromatic adaptation applied?

See, with a linear bradford color adaption transformation the original saturated blues and some whites of Adobe RGB (D65), i.e. Adobe 1998, get stripped off when you transfer it to Adobe RGB (D50) and later onto Prophoto RGB (D50).

Incidently, nobody has paid any attention to my case (2). If you want full preservation of Adobe gamut to Prophoto, this is the mode to look at.

Joofa
« Last Edit: January 04, 2011, 10:22:07 pm by joofa »
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degrub

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #237 on: January 04, 2011, 10:22:05 pm »

yawn....There is probably enough in this thread for a technical paper or two. Why not write your thesis and present at CIC in November ?

http://www.imaging.org/ist/Conferences/cic/index.cfm

« Last Edit: January 04, 2011, 10:44:12 pm by degrub »
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Schewe

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #238 on: January 04, 2011, 10:55:17 pm »

See, with a linear bradford color adaption transformation the original saturated blues and some whites of Adobe RGB (D65), i.e. Adobe 1998, get stripped off when you transfer it to Adobe RGB (D50) and later onto Prophoto RGB (D50).

Uh huh...what happens when you transform Adobe RGB (1998) to ProPhoto RGB directly using any of the currently available CMMs?
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #239 on: January 04, 2011, 11:37:26 pm »

Uh huh...what happens when you transform Adobe RGB (1998) to ProPhoto RGB directly using any of the currently available CMMs?

Hi,

I am not an expert on commercially available CMMs. But, what I hear from more knowledgeable posters in this thread is that they like to do a chromatic adaption from D65 to D50, perhaps using a linear matrix like Bradford transform.

Regards,

Joofa
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