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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 228212 times)

MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #180 on: January 04, 2011, 03:27:34 pm »

Quote from: Iliah
Colour science is not "frozen". Fairchild, anybody
Your point is well taken. I have Mark Fairchild's Color Appearance Models and it is excellent. Color science is still changing and the work he and others are doing on advanced color models is really cool.

Quote from: Joofa
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

OK good, we agree on this; these are two sets of XYZ numbers. They are different XYZ numbers. Unanimous agreement. But the crux of the the problem is this question: are they two different colors? Colorimetry can only answer that and other questions if we assume the same viewing conditions. XYZ coordinates are absolute, but can't really be described as colors without more information. It they could, all our problems would be solved—we would just use XYZ coordinates anytime we wanted to communicate color.

Lets look at our people with the house again: person A inside with a tungsten light and person B outside at dusk. Now ask them this question: does the color of the lightbulb fit inside a greyscale gamut? Person A is going to say, "sure it obviously does, the color of the lightbulb is white, In our greyscale space that is around [255]." Person B is going to say, "Not so fast, that lightbulb is yellow. It lies outside the gamut greyscale." But it's the same XYZ coordinate.

If only the people could communicate the color of the lightbulb rather than the XYZ coordinates.

They can. And this is why we have colorspaces. Both people can convert the coordinates to LAB space. To get to LAB they need to figure out a white point. Person A will use one that corresponds roughly to the 3200K tungsten and will get a LAB value like [95, 0, 0]. Person B will use a white point to something like 12000K and get a lab value [95, 0, 40].

NOW we can talk about color. Person A and B can pull up their LAB values on computer. Person A will recognize the white color as theirs and person B will identify the yellow as theirs. If they want to understand the difference between these colors they can go back to their LAB calculations where they'll see the cause of their different perceptions. They'll also see that if they want to know if it fits into a greyscale gamut, they'll also have to define that gamut in LAB or a similar space.

This is how I read your argument: There is person A inside in a well defined D50 environment. They have just decided that color A defined under D50 fits in a greyscale gamut also defined under D50. You are person B outside in the dusk screaming that color A obviously doesn't fit in a greyscale gamut. And you're right, from the point of view of person B it doesn't. But it doesn't matter. There are infinite different viewing conditions where that D50 light is not going to look white.
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #181 on: January 04, 2011, 03:33:05 pm »

ACE doesn't show clipping as it converts recol.

How can you confirm this?
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #182 on: January 04, 2011, 03:34:48 pm »

Hi Mark,

I think you are still not getting what I am trying to say. It is not complicated. Please think how the original experiments were done to determine color matching functions. In this case your measurement system is Prophoto RGB (D50), and I shine a color, which incidently happens to be the blue primary of Adobe RGB (D65). Just like the original experimenters, your job is to match this color using Prophoto RGB (D50) using linear methods. You will find you are unable to match this unless you raise your blue saturation to more than "unit stimulus" saturation.

That is what I have been saying all along.

Best regards,

Joofa
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #183 on: January 04, 2011, 03:39:07 pm »

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.

There is zero difference using either RelCol or ABS (as I’d expect) with ACE. The Apple CMM shows far less and different clipping than the illustration from MS.

One of these CMM’s isn’t kosher, so which?
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #184 on: January 04, 2011, 03:59:15 pm »

Quote
ACE doesn't show clipping as it converts recol.
How can you confirm this?
convert from Adobe to ProPhoto first relcol and secondly abscol. Assemble the two files on a layer and set the layer mode to "difference". View the histogram ... no difference.

edit:
BTW: "AdobeCMM" does take the white point into account (see attachments - source: "ECI-RGB", D50 | target: AdobeRGB)
« Last Edit: January 04, 2011, 04:29:23 pm by tho_mas »
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #185 on: January 04, 2011, 04:10:07 pm »

I think you are still not getting what I am trying to say. It is not complicated. Please think how the original experiments were done to determine color matching functions. In this case your measurement system is Prophoto RGB (D50), and I shine a color, which incidently happens to be the blue primary of Adobe RGB (D65). Just like the original experimenters, your job is to match this color using Prophoto RGB (D50) using linear methods. You will find you are unable to match this unless you raise your blue saturation to more than "unit stimulus" saturation.

I understand what are saying. But the point of moving from one color space to another is to have the colors match. If a color in one space can't produce a match in another it's out of gamut, right. I'm pretty sure we agree on that.

So let's do your experiment. Let's say we are under D50 (knowing that already we doing the experiment differently that the original which didn't specify). You shine a light of your D65 Adobe RGB primary. We know its XYZ value: [ 0.1881852  0.0752741  0.9911085]. So I'm under D50 and seeing this color.

Here is the question: is this color that I am seeing, the color we mean when we say [0, 0, 255] in AdobeRGB? The answer is no. The color we mean when we say [0, 0, 255] in ARGB is a different set of XYZ numbers under D50.  

There are ways to look at this experimentally using haploscopic tests which allow us to see colors with each eye under different adaptation. It works like this:

Your left eye is adapted to D65 and we show you the XYZ numbers above and ask, is this the color you are trying to achieve with adobRGB [0, 0, 255]? You would say yes! There is it.

Your right eye is adapted to D50 and we show you the same XYZ numbers and ask the same question. The answer in this case is no. You would say you are seeing a different color in each eye. Only one of them can accurately be called [0, 0, 255] adobeRGB.  

Now we let you adjust the color in your right eye until they match. After fiddling with some dials you would arrive on a number that corresponds to XYZ [ 0.149224   0.0632197  0.7448387]. Now you are seeing a match between the two eyes. Your right eye is now seeing what your left eye confirmed was adobeRGB [0, 0, 255]. Convert this number into ProPhoto space and you will see that is easily fits.

The problem you are bumping into is that you are talking about XYZ numbers like they are color perceptions, but they're not.
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fdisilvestro

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #186 on: January 04, 2011, 04:32:04 pm »

I emailed Bruce Lindbloom about this issue,

He kindly answered me, even read the thread, an allowed me to quote his answer in the forum (I put bold on what I consider key issues):

Quote
The resolution of the issues boils down to agreement of the premises. If one takes the position that AdobeRGB blue lies outside the gamut of ProPhotoRGB, then one must also agree that the AdobeRGB grayscale (R=G=B) is not neutral. This is the case where chromatic adaptation is not used (absolute colorimetric). AdobeRGB and ProPhotoRGB whites are outside of each other’s gamuts.

I believe that all of the reference RGB color systems share the basic premise that R=G=B is neutral. Of course, neutral is relative to the color system’s reference white. When considering two RGB systems having different reference whites, the only way to reconcile the neutrality of the grayscales is to use chromatic adaptation (relative colorimetric). In most real-world applications and workflows, this is the only thing that makes practical sense. It is what ICC, Photoshop, Lightroom, etc. are based on. Although AdobeRGB is specified relative to D65, its ICC profile contains the primaries adapted from D65 to D50 using the Bradford chromatic adaptation method (use a profile inspector to examine the rXYZ, gXYZ and bXYZ tag contents). So any ICC-aware app that uses this profile is transforming colors in the D50 world, not D65. R=G=B is a D50 neutral, no matter what the native reference white of the color space.

If one agrees that R=G=B is neutral for both profiles, regardless of the reference whites, then chromatic adaptation must be used to bring them both to the same reference. In that context, AdobeRGB blue lies inside the gamut of ProPhotoRGB.

Regards,

Bruce
--
Bruce J. Lindbloom


So, as I understand it, both sides of the discussion can be right, it depends on the premises you choose to follow

For my regular work, I take the practical approach of adobeRGB being contained in ProPhotoRGB using illuminant D50

digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #187 on: January 04, 2011, 04:46:29 pm »

So, as I understand it, both sides of the discussion can be right, it depends on the premises you choose to follow

Thanks a kind way of putting it <g>.

So the idea is, we can bastardize one of these well defined working spaces, working spaces that otherwise function properly and as designed, being well behaved where R=G=B (a big advantage of such editing spaces) to illustrate a pretty useless theoretical construct where some colors fall outside the gamut of the spaces seems like a lot of mental masturbation. And as I asked, for what purpose? That was never answered, I suspect it never will be (much like my query as to why the flat earth proponent here is unwilling to view the gamuts as oh so many utilities properly map them as they are intended to be used). Its a bit like those who say bumblebees can’t fly. Why anyone would spend so much time and effort to make a point that has no useful basis in the real world will probably never be answered.

Quote
In most real-world applications and workflows, this is the only thing that makes practical sense.
Quote
For my regular work, I take the practical approach of adobeRGB being contained in ProPhotoRGB using illuminant D50

Indeed! How nice to get back to planet earth.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #188 on: January 04, 2011, 04:58:11 pm »

I emailed Bruce Lindbloom about this issue,

He kindly answered me, even read the thread, an allowed me to quote his answer in the forum (I put bold on what I consider key issues):


So, as I understand it, both sides of the discussion can be right, it depends on the premises you choose to follow

For my regular work, I take the practical approach of adobeRGB being contained in ProPhotoRGB using illuminant D50

Hi Francisco,

Thanks for the message and the kind effort to get clarification from Bruce Lindbloom. What Bruce said was already present in my first message in my note and I copy it below, see cases (1) and (3), below. While, I also worked out two additional cases, (2) and (4) below.

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

Thanks again.

Sincerely,

Joofa
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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #189 on: January 04, 2011, 05:41:00 pm »

The problem here is misuse of the Bruce color calculator.  From Page 1 post 15...

You have highlighted the incorrect parameter. See the drop-down above where you have circled. It clearly says D50. Please change that to D65 for this Adobe RGB. However, when you go to ProPhoto calculation change that back to D50.

This is your first problem.  Bjanes correctly pointed out, three posts prior to the post quoted above, that the “Ref White” value is the desired illuminant for the CIE spaces...it is not an override of the white point for the selected RGB space.

The D50 on the calculator refers to the white point of the reference (XYZ) space.

You have misinterpreted the meaning of that Ref White value.  Once you select an illuminant for the CIE spaces, you can’t change it because that assigns a completely different color to the current CIE values.

So you calculated one color under one illuminant, then before translating that color to Pro Photo, you selected a different illuminant...thereby changing the color that your CIE values represent.

Here is your second problem with using the calculator...

There is no need for a Bradford transformation here as we are doing a direct measurement of two visually different colors A and B in a measurement system using ProPhoto RGB scaled to D50 white point.

In the help for his calculator, Bruce LindBloom notes that when the selected CIE illuminant is different from the white point of the color space, then an adaptation is necessary.

All this was already explained by jbrembat in post 110.


Well, I’m solidly convinced that Adobe RGB blues (and sRGB blues, which are also out of gamut if you use joofa’s method) are within the Pro Photo space.

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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #190 on: January 04, 2011, 05:43:31 pm »

The problem here is misuse of the Bruce color calculator.  From Page 1 post 15...

Here comes another contender  ;D. Please see the attachment to Iliah Borg's first message in this thread to figure out how to use Bruce Lindbloom's calculator. BTW, I personally did not use his calculator. Do you think his calculator would have let me make all those 3D graphs that I presented?

Sincerely,

Joofa
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Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #191 on: January 04, 2011, 06:02:38 pm »

Here comes another contender  ;D. Please see the attachment to Iliah Borg's first message in this thread to figure out how to use Bruce Lindbloom's calculator.

He made the same exact mistake.  He even admits it...

It is not wrong, I forced "assign", which explains what is happening.

There’s no assigning of white points.  The “Ref White” field is the illuminant for the CIE spaces.  That's his mistake.  Every space has its white point...Adobe RGB has D65, Pro Photo has D50, and CIE has whatever is set in “Ref White.”  The calculator doesn’t allow you to change the white point of the RGB color spaces.

Once you choose an illuminant for the CIE spaces, you don’t change it during your conversions.  That’s like trying to calculate how many miles you drove at 50 MPH for 37 minutes, and then somewhere in the middle of your calculations labeling your miles as kilometers…that doesn’t work.
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Farmer

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #192 on: January 04, 2011, 06:04:59 pm »

It's pretty simple, it seems.

Joofa, you're right, so long as we create a premise that allows you to be right, which has no apparent impact or utility on real-world application as relates to this place (ie photography).

In all useful and practical cases, you're wrong, because the initial premise doesn't meet your criteria.

As an intellectual exercise, it has merit.  As a practical instruction or guide, it does not.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #193 on: January 04, 2011, 06:15:23 pm »

It's pretty simple, it seems.

Joofa, you're right, so long as we create a premise that allows you to be right, which has no apparent impact or utility on real-world application as relates to this place (ie photography).

In all useful and practical cases, you're wrong, because the initial premise doesn't meet your criteria.

As an intellectual exercise, it has merit.  As a practical instruction or guide, it does not.

Farmer, I don't think you are being fair here. If I had listed only case (1) in my note and insisted that is the only option then it would have been something. I clearly provided 4 different cases so that people can understand what is going on here.

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. :D And, now they are clinging on to the Adobe RGB (D50) as if their life depended on it.

Regards,

Joofa
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #194 on: January 04, 2011, 06:24:08 pm »

He made the same exact mistake.  He even admits it...

I notice the tag below your username says "newbie".

Joofa
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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #195 on: January 04, 2011, 06:26:57 pm »

I notice the tag below your username says "newbie".

I notice that's the kind of thing said by people who finally realize they're wrong.
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Schewe

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #196 on: January 04, 2011, 06:27:36 pm »

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. :D And, now they are clinging on to the Adobe RGB (D50) as if their life depended on it.

Well, congratulations...you now have a color space named after you. You are in rare company such as Bruce (Fraser) RGB (a variant also from Adobe RGB) as well as Melissa RGB. The "s" of sRGB doesn't really stand for Stokes RGB (but it does in my mind).

But while you may have won a battle, you've lost the war. ProPhoto RGB is STILL the ONLY color space I know of that can contain ALL the colors a camera can capture and ALL the colors modern inkjets can print. And if Bruce L. says all of Adobe RGB can fit within ProPhoto RGB than I don't think I can accept your contention that any color in Adobe RGB will be clipped in ProPhoto RGB. That's what the last several pages of posts were about, right?

Wow, I'm worn out :~)
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #197 on: January 04, 2011, 06:30:58 pm »

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. :D And, now they are clinging on to the Adobe RGB (D50) as if their life depended on it.

As long as you are amused... If you would simply go back to post #16, you’ll clearly see:

Quote
The WP of Adobe RGB (1998) is D65. Its as simple as that. If you try to define the space using D50, it ain’t Adobe RGB (1998) anymore. Go ahead and call it joofaRGB. <G>

The same items were pointed out to you in post 36, 42, 68, 151,159 etc.

So yes, we absolutely realized that “Adobe RGB“ (D50) as written above, could be called joffaRGB, that Adobe RGB (1998) (D65) is Adobe RGB (1998)!
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #198 on: January 04, 2011, 06:35:19 pm »

Well, congratulations...you now have a color space named after you. You are in rare company such as Bruce (Fraser) RGB (a variant also from Adobe RGB) as well as Melissa RGB. The "s" of sRGB doesn't really stand for Stokes RGB (but it does in my mind).

But while you may have won a battle, you've lost the war. ProPhoto RGB is STILL the ONLY color space I know of that can contain ALL the colors a camera can capture and ALL the colors modern inkjets can print. And if Bruce L. says all of Adobe RGB can fit within ProPhoto RGB than I don't think I can accept your contention that any color in Adobe RGB will be clipped in ProPhoto RGB. That's what the last several pages of posts were about, right?

Wow, I'm worn out :~)


Hi,

No, Bruce L. has said what is my case (3), only Adobe RGB (D50) can be contained within ProPhoto RGB (D50). If you read his note he clearly says that the case (1) can't be contained, i.e., Adobe RGB (D65) can't be contained within Prophoto RGB (D50).

Quote
This is what Bruce says:

"If one takes the position that AdobeRGB blue lies outside the gamut of ProPhotoRGB, then one must also agree that the AdobeRGB grayscale (R=G=B) is not neutral. This is the case where chromatic adaptation is not used (absolute colorimetric). AdobeRGB and ProPhotoRGB whites are outside of each other’s gamuts."

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.

Best regards,

Joofa
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #199 on: January 04, 2011, 06:38:52 pm »

As long as you are amused... If you would simply go back to post #16, you’ll clearly see:

The same items were pointed out to you in post 36, 42, 68, 151,159 etc.

So yes, we absolutely realized that “Adobe RGB“ (D50) as written above, could be called joffaRGB, that Adobe RGB (1998) (D65) is Adobe RGB (1998)!


Ha ha, Digital Dog, you have still not realized that the gamuts of Adobe RGB you saw that you claimed were within Prophoto RGB were of Adobe RGB (D50) = JoofaSpace, and not Adobe RGB (D65). You really need to study color science.

Joofa
« Last Edit: January 04, 2011, 06:41:13 pm by joofa »
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