attention color whizes: non-typical sRGB/RGB/ProPhoto question

[Iliah]

Incorrectly.

Define "correctly" than and explain why while doing everything "by the book" local colour editing to get correct skin tones, sky tint, foliage colour is needed.

[jc1]

Hi all,

I am slow in catching up.
More gamut plots for refreshment.
 

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 [0.188185   0.075274   0.991108] is non-existence in Abode 1998 D50. Comparison is hence in valid.
 

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.

I thought that is the main function of CMM which maps with selected rendering intent, the vector from one space to another space.
All mapped vectors possess at least two things in common:
1) same viewing condition
2) within the defined gamut

with best regards

[tho_mas]

explain why while doing everything "by the book" local colour editing to get correct skin tones, sky tint, foliage colour is needed.

your skin tones contain high saturated blues?

[Farmer]

your skin tones contain high saturated blues?

Andorians?

[jbrembat]

BTW, I note with mild amusement that people who were accusing me of creating a new space ("JoofaSpace"), still don't realize that Adobe RGB (D50) is, if anything, a Joofaspace, because it has been changed from the standardized definition of Adobe RGB (D65) to conform to D50 white point! So ironic. Cheesy And, now they are clinging on to the Adobe RGB (D50) as if their life depended on it.

Does not exist Adobe RGB (D50), you are very confused again.
Adobe RGB is D65, by definition.
The transform D65=>D50 is for adapting white point to the destination color space.
If your destination is a D55 color space, the adaptation will be D65=>D55.
In other words you are not changing Adobe RGB definition for each destination gamut, you are scaling the white point in XYZ.

Your mistake is to transform Adobe RGB to ProPhoto RGB without white point scaling. It seems you are not interested on colors, but only on numbers.

Let me try to explain what are you doing:
we know that
- 1 inch=2.54 cm.
- now we are free to fix the unit of measure, and we say that 2.54 are meters (we are going from cgs reference sytem to MKS reference system without scaling)
- conclusion 1 inch=2.54 meters

Without scaling between reference systems you can get any wrong value.

Lindbloom tried to explain that you are wrong using gray values.
But another time you ignore (or don't understand) what he said.

The reason Adobe RGB (50) can be contained is that because it has been chormatic-adaptation-transformed from Adobe RGB (D65), and this process has already stripped that offending blue Adobe RGB (D65) primary. After Bradford transformation Adobe RGB (D50) gets a new blue primary.

Wrong. Adobe RGB blue primary is not changed.
-When you go from Adobe RGB blue primary to XYZ, the computation is performed using D65, by definition of Adobe RGB
-the scaling is for XYZ, depending on destination color space white reference

From a mathematical point of view you can adapt Adobe RGB blue primary to any white point different from D65 to go from Adobe RGB to any other color space, but that doesn't mean you are changing Adobe RGB blue primary.
You are computing good XYZ values for the appearance of Adobe RGB blue color on different reference systems.
 
If you don't scale but change the reference system, you get a number XYZ that is no more representative of Adobe RGB blu.



Jacopo

[Graystar]

Define "correctly"

“Correctly” means to convert the blue from one space into a blue in another space that appears, to a human, to look exactly like the blue in the first space.  To get such a color you MUST apply adaptation when the white points are different because a human will apply adaptation when the white points are different (the very reason why we have adaptation.)  Otherwise the blue that you calculate will NOT look the same to a human...it’s just the result of a half-processed conversion.

and explain why while doing everything "by the book" local colour editing to get correct skin tones, sky tint, foliage colour is needed.

That's a question that can be seen from a 1000 different angles.  Without examples of what you're referring to and and explanation of what you were trying to accomplish, I can't answer such a question.

[Graystar]

Let me try to explain what are you doing:
we know that
- 1 inch=2.54 cm.
- now we are free to fix the unit of measure, and we say that 2.54 are meters (we are going from cgs reference sytem to MKS reference system without scaling)
- conclusion 1 inch=2.54 meters

Without scaling between reference systems you can get any wrong value.

I too explained with analogies and I think a couple others as well.  It's just not sinking in that they're not keeping the same blue by merely specifying a different XYZ white point for the conversion.

The XYZ blue may be strictly defined, but the Adobe 255 blue, as represented by XYZ, only exists as a relationship between the coordinates of the color and the coordinates of the white point.  If you now simply select a different white point, you’ve changed the relationship, and thus have changed the blue.  It's so obviously that they can’t see it.

Joofa and Iliah...if you use your process with sRGB you get the same result...that there are sRGB blues outside of Pro Photo.  Do you claim that sRGB has blues that Pro Photo doesn’t?

[joofa]

Thank you jc1 for those beautiful plots. I don't think there should be any doubt left in anybody's mind now that Adobe RGB (D65), the official specification, has blues (and some whites) that are outside the gamut of chromatically-adapted (linear bradford transformed) Adobe RGB (D50), and henceforth to Prophoto RGB (D50).

So all those gamuts that have been claimed as showing Adobe RGB gamut within Prophoto gamut were showing Adobe RGB (D50) within Prophoto RGB (D50) and not Adobe RGB (D65) within Prophoto RGB (D50).

Sincerely,

Joofa

[Graystar]

More gamut plots for refreshment.

Now do it for sRGB.

[digitaldog]

Does not exist Adobe RGB (D50), you are very confused again.
Adobe RGB is D65, by definition.
The transform D65=>D50 is for adapting white point to the destination color space.

Your mistake is to transform Adobe RGB to ProPhoto RGB without white point scaling. It seems you are not interested on colors, but only on numbers.

Agreed, and when I tried to point this out in my last post, referencing 5 other posts explaining the same facts, I was given an insulting and childish reply. At this point, I can only believe we are trying to engage in conversation with a troll or someone who has a religious belief system with regards to color outside the real world. Such debates are pointless. Normally I’d agree to disagree but the behavior and curt answers, refusal to answer other salient questions means that for me, its best to ignore joofa. But there were some very good posts from others that provided what could be a basis for an excellent white paper or article on color.

[Graystar]

Thank you jc1 for those beautiful plots. I don't think there should be any doubt left in anybody's mind now that Adobe RGB (D65), the official specification, has blues (and some whites) that are outside the gamut of chromatically-adapted (linear bradford transformed) Adobe RGB (D50), and henceforth to Prophoto RGB (D50).

I take it this means that you're just going to ignore my question?  Here it is again...

Joofa and Iliah...if you use your process with sRGB you get the same result...that there are sRGB blues outside of Pro Photo.  Do you claim that sRGB has blues that Pro Photo doesn’t?

[tgray]

I'm not a color expert.  However, I think joofa knows that for most purposes you want to use a chromatical adaption when going from one color space to another.  I also think he knows that AdobeRGB is not D50.  He's stated repeatedly that what he calls 'AdobeRGB (D50)' is AdobeRGB with a transform to use a D50 white point.  For lack of a better name, he labeled it 'AdobeRGB (D50)'.  He's also stated repeatedly, ever since his first post on dpreview, that his argument is based on a specific transform without chromatic adaptation.

You guys seem to be arguing about semantics, and not in a good way.  And while I'm an empiricist at heart and do it for a living, just to brush away an argument/statement by saying it has no real world applications is short sighted.  Bruce Lindbloom seemed to confirm what joofa was saying, though with the caveat that most people would never want to transform color that way, i.e. we want R=G=B to be neutral and not have a color cast.

In my opinion, this seems to be mostly an academic exercise.  I think that was pretty clear from the beginning.  I don't mean that in a bad way at all.  A lot of good things have come from those thought processes.  Hell, a lot of this color science was done long before we were worrying about color managed digital photo workflows. And Iliah has hinted at some situations where it might not be just academic.

My summary of 13 pages of threads: "joofa, you're wrong.  Oh nevermind, you're not wrong, but only while a certain set of conditions are satisfied (ones you clearly stated at the start).  However, since those conditions aren't relevant to the way I work in the 'real world', I'm going to continue to treat you like you're wrong."

Joofa, correct me if I'm wrong here and stepping over my bounds.  I learned some interesting things from this discussion.

[digitaldog]

Bruce Lindbloom seemed to confirm what joofa was saying, though with the caveat that most people would never want to transform color that way, i.e. we want R=G=B to be neutral and not have a color cast.

More than don’t want. The question has been asked (and ignored): just why or how can the proposed transforms, (outside Bruce’s calculator or a similar utility that spits out numbers) produce the results this academic exercise predicts? Photoshop? Lightroom? C1? Any available product that would utilize the two profiles in question? And if so WHY?

Please examine Jacopo‘s last post and excellent analogy of cm and meters.

[Peter_DL]

Do you claim that sRGB has blues that Pro Photo doesn’t?

Yes of course it has, in an AbsCol sense, starting with sRGB D65 white and stretching to the blues.

Actually, it is you making a quite strong claim and assumption: that human chromatic adaptation to a different illumint would be perfect,
and that it would be perfectly implemented with current RelCol wp mapping according von Kries, Bradford, etc... Somehow I doubt.

Let's better consider a numerically correct but perceptionally wrong starting point than the other way round. Numerical correctness never was the final goal, but it often makes a better starting point to explore appearence.

Peter

--

[Iliah]

your skin tones contain high saturated blues?

Is it your idea of sarcasm? Or you seriously think the problem of inefficiency and insufficiency of modern colour management affects only blues?

[Iliah]

“Correctly” means to convert the blue from one space into a blue in another space that appears, to a human, to look exactly like the blue in the first space.  To get such a color you MUST apply adaptation when the white points are different because a human will apply adaptation when the white points are different (the very reason why we have adaptation.)  Otherwise the blue that you calculate will NOT look the same to a human...it’s just the result of a half-processed conversion.

That's a question that can be seen from a 1000 different angles.  Without examples of what you're referring to and and explanation of what you were trying to accomplish, I can't answer such a question.

Well, you do not understand that the better model of the situation is: several colour spaces coexist in the same scene. It is nearly always the case. So, your suggestion to convert is not the correct method to preserve appearance.

You can't answer not because you do not have examples. You do have them on your own photos, but you either ignore them or you can't see the reason. However the reason is physics which happens to disagree with boxed approach of data processing in colour management.

[Graystar]

Yes of course it has, in an AbsCol sense, starting with sRGB D65 white and stretching to the blues.

But an absolute colormetric conversion results in color shifts, as explained by Sean McHugh over at Cambridge in Colour...

"The exact preservation of colors may sound appealing, however relative colorimetric adjusts the white point for a reason. Without this adjustment, absolute colorimetric results in unsightly image color shifts, and is thus rarely of interest to photographers.

This color shift results because the white point of the color space usually needs to align with that of the light source or paper tint used."

http://www.cambridgeincolour.com/tutorials/color-space-conversion.htm

[Peter_DL]

.. just why or how can the proposed transforms, (outside Bruce’s calculator or a similar utility that spits out numbers) produce the results this academic exercise predicts?

Let's have an image in Adobe RGB in Photoshop, let's assume that we want to appear it "cooler".
One option is to convert to ProPhoto RGB, Intent: Absolute Colorimetric, Engine: Microsoft ICM (or Apple's CMM).
Oh, take care about clipping along white to blue hues.

Peter

--

[MarkM]

Let's better consider a numerically correct but perceptionally wrong starting point than the other way round.

That's the problem in a nutshell: the numbers are designed to model perception; it's the whole point. If they are perceptionally wrong for no reason, they are wrong. I can say miles and feet are the same thing if I divide the mile by 5280. My math is right, the numbers are right, but I'm still wrong.

But an absolute colormetric conversion results in color shifts

This is true, but I think most people are misunderstanding the process for absolute colorimetric conversions. The correction of chromatic adaptation is a different step than scaling white points.  The spec tells you to first chromatically adapt the tristimulus values (including the media white point) and then (in rel col) scale for the white point.

The spec is here if your really interested: http://www.color.org/ICC1v42_2006-05.pdf

Here are the relevant bits (again):
6.2.2   Media-relative colorimetric intentsTransformations for this intent shall re-scale the in-gamut, chromatically adapted tristimulus values such that the white point of the actual medium is mapped

6.2.3   ICC-absolute colorimetric intentTransformations for this intent shall leave the chromatically adapted tristimulus values of the in-gamut colours unchanged.

If you follow the recipe that occurs after this in the spec, you will see where the white point scaling happens in relative colorimetric. It is not a chromatic adaptation at that point: you simply multiply your values by the ratio between the two (chromatically adapted white points).  Adobe CMM seems to do this correctly.

[tho_mas]

your skin tones contain high saturated blues?

Is it your idea of sarcasm? Or you seriously think the problem of inefficiency and insufficiency of modern colour management affects only blues?

no, the discussion just happened to evolve around bright, high saturated blues of AdobeRGB clipping in ProPhotoRGB.
As I use neither AdobeRGB nor ProPhotoRGB maybe I am overlooking something. In any case it is possible to preserve all the colors your camera can capture in one color space. Maybe not in Adobe products, but that's a different story. In terms of color management I am finding ACR + LR pretty unusable anyway. Which is again a different story.
Me personally I first think about limited gamuts and color shifts when priniting. But that's a given fact... simply as the capabilities of printers are limited. Therefore I have no idea in how far (where/why) you struggle with the "inefficiency and insufficiency of modern colour management". If we talk for instance about inaccurate white and black points of papers... or anything related to "simulate" a different color appearance on different media... I'm with you. But I am under the impression that you are experiencing limitations on the level of capture & raw-processing. And, again, I don't get the point you are making.