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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 227701 times)

Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #300 on: January 05, 2011, 02:33:03 pm »

> Let me remind you what you said in post 282: "Some other companies are certainly do however." Your words.

I was answering you question. Now you can check the list of sponsoring companies.

> There are uncounted numbers of academics all with a "better" idea

I hope in your comment you do not mean Fairchild.
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jbrembat

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #301 on: January 05, 2011, 03:23:38 pm »

Quote
I don't know why Prophoto was standardized at D50 and not at D65.
There are many things you don't know.
Prophoto was developed for reflectives media (prints). D50 is the standard for prints.
But for color management, a white point of D65 doesn't change anything.
Of course matrices to go from/to XYZ should be different.

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You need to start from the basics. White balance is the form of chromatic adaptation.
Chromatic adaptation for color space conversion is not white balance.
Again you are mixing things.

Adaptation for different white references of color spaces has nothing to do with adaptation for white balance.

You think you can do white balance using a conversion between color spaces. But you can't.
You really need to start from the basics.

Color management target is "preserving colors between color spaces". It is not for white balance.


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1 inch no longer remains 2.54cm!
Better than Einstein restricted relativity!
And then your AdobeRGB blue is no more the same color.
You stated that starting from a causual XYZ value (not AdobeRGB blue primary) you can go out of ProPhoto.
I can say more:
starting from an XYZ value you can go out from visible colors.
Very nice sentence. LOL

Jacopo
« Last Edit: January 05, 2011, 03:25:18 pm by jbrembat »
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #302 on: January 05, 2011, 03:30:33 pm »

But for color management, a white point of D65 doesn't change anything.
Of course matrices to go from/to XYZ should be different.

So, if D65 does not change anything then why does the matrix change?

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Chromatic adaptation for color space conversion is not white balance.

Hmmm.......

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Better than Einstein restricted relativity!

Isn't that cool? Color theory and relativity. BTW, do you know that famous physicsts Maxwell and Nobel laureate Schrodinger, among others, did important work in color theory. It appears that our own Emil Martinec is interested in color also? What color attracts physicists?

Sincerely,

Joofa
« Last Edit: January 05, 2011, 07:29:25 pm by joofa »
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #303 on: January 05, 2011, 03:35:21 pm »

"In color science, chromatic adaptation is the estimation of the representation of an object under a different light source than the one in which it was recorded."

"A common application is to find a chromatic adaptation transform (CAT) that will make the recording of a neutral object appear neutral (color balance), while keeping other colors also looking realistic."

See http://en.wikipedia.org/wiki/Color_balance , read the report ISBN 978 3 901906 30 5, and come back after that.
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #304 on: January 05, 2011, 03:43:15 pm »

There are many things you don't know.
Prophoto was developed for reflectives media (prints). D50 is the standard for prints.

Other reasons are spelled out here:
http://www.photo-lovers.org/pdf/color/romm.pdf
http://www.kodak.com/global/plugins/acrobat/en/professional/products/software/colorFlow/romm_rgb.pdf
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Peter_DL

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #305 on: January 05, 2011, 03:45:58 pm »

That is an interesting proposition, but we usually do not want the colors to shift and use relative colorimetric.

Bill,

Aside from RelCel, it was suggested that White balance is also a form of chromatic adaptation in order to map source white to target white. And we really would not want to "relcol" i.e. to click-whitebalance every image in the Raw converter. Often enough we find it desirable to preserve a bit of the original illuminant & scene white in order to preserve the mood of a scene (let’s call it partially AbsCol). Chromatic adaptation is not perfect in my eyes.

So in total we do not necessarily have a strict RelCol mapping / chromatic adaptation from scene white to monitor white. As for the working space in-between, the question remains about the influence of its white point. Could Adobe RGB D65 really hold specific colors from a scene that are de facto outside ProPhotoRGB D50 in an absolute colorimetric sense, let’s say if we could replace the linear-gamma-ProPhoto RGB version inside ACR by a corresponding linear-gamma-Adobe RGB space. Sorry – I don’t know.

I’d agree that the "barrel capacity" of ProPhoto RGB is probably not the first thing to be concerned about it. Discussion was interesting though.

Kind regards,
Peter

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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #306 on: January 05, 2011, 03:47:19 pm »

Thanks for the references, Digital Dog.

Sincerely,

Joofa
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #307 on: January 05, 2011, 03:50:47 pm »

Could Adobe RGB D65 really hold specific colors from a scene that are de facto outside ProPhotoRGB D50 in an absolute colorimetric sense, let’s say if we could replace the linear-gamma-ProPhoto RGB version inside ACR by a corresponding linear-gamma-Adobe RGB space. Sorry – I don’t know.
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Why not use Prophoto RGB (D65)? It can have all of Adobe RGB (D65) contained within.

Joofa
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Peter_DL

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #308 on: January 05, 2011, 04:15:12 pm »

Why not use Prophoto RGB (D65)? It can have all of Adobe RGB (D65) contained within.

Joofa, - even for me the purely theoretical part is now over,
and you may note that I was very open to your mindset.

IMO the task now is to come up with a practical example and some real-world images for illustration.
I've been asking Iliah but please feel invited as well.

Cheers! Peter

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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #309 on: January 05, 2011, 04:15:18 pm »

Why not use Prophoto RGB (D65)? It can have all of Adobe RGB (D65) contained within.
why not use a D50 color space large enough to contain all the colors a camera could capture potentially?
I assume C1's internal colour space meets these requirements. Not sure, though. In any case it seems to be an extremely large colour space.
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Iliah

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #310 on: January 05, 2011, 04:20:06 pm »

> IMO the task now is to come up with a practical example and some real-world images for illustration.

Illustration of what, please? That colour perception is not restricted to relative colorimetric?
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #311 on: January 05, 2011, 04:20:30 pm »

why not use a D50 color space large enough to contain all the colors a camera could capture potentially?

You can't increase the "gamut" of a particular color space arbitrarily. It is tied to the white point and primaries. So Adobe RGB (D50 or D65) has a gamut what it has. But Prophoto RGB (D65) includes those troublesome areas of Adobe RGB (D65) which are not represented in Prophoto RGB (D50), and hey, you also get the same white point.

On the other hand one way to "mathematically" increase the gamut is:

(1) If you let overstaturation - more than unit stimulus.
(2) Negative coefficients for tristimulus.

Actually, with both (1) and (2) above, the whole concept of gamut crumbles, because now you can span all of the color space.

Sincerely,

Joofa

EDIT: Modified. Several typos.
« Last Edit: January 05, 2011, 04:55:45 pm by joofa »
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Joofa
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #312 on: January 05, 2011, 04:25:00 pm »

You can't increase the "gamut" of a particular color space arbitrarily. It is tied to the white point and primaries.
does this also apply to table based profiles? IMO only to matrix based profiles...
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #313 on: January 05, 2011, 04:28:01 pm »

does this also apply to table based profiles? IMO only to matrix based profiles...

I was not thinking in terms of profiles when I wrote that. I was thinking of a standard definition of a linear color space that I have given before. Human vision is considered to have 3 dimensions, so it is a 3D space. The 4th vector (white point) is there to set units.

Joofa
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Graystar

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #314 on: January 05, 2011, 04:29:29 pm »

OMG...I can’t believe this needs to be explained…

White balance changes colors.

Adaptation keeps colors the same.

Put another way...white balance results in a change to the color response of the human eye.  Adaptation maintains the color response of the human eye.

If you use Iliah’s method of using the Bruce Lindbloom calculator to convert not 0,0,255...but 128,128,128 from Adobe to Pro Photo...you’ll see that the resulting conversion is not neutral.  Hence, the color has changed.  The only way to get a neutral result (that is to say, the same color response) is to use adaptation.  When this is done, the calculator calculates equal values of RGB for the Pro Photo space.
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jbrembat

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #315 on: January 05, 2011, 04:31:22 pm »

Quote
So, if D65 does not change anything then why does the matrix change?
When you build an RGB color space, you have to fix :
red,green,blue primaries,white point and a transform to go from/to linear RGB values and nonlinear RGB values (this is what is named "gamma" encoding, as many color spaces use a power nonlinear function, power=gamma).
Starting from this set of values, you can define how to go to/from XYZ.
CIE_XYZ is the mother of any color space.
If you change the white reference, the matrices reflect this change.

This is the reason you cannot change white reference without adaptation when you convert from a color space to a different color space with a different white point.

The matrices to/from XYZ are white reference dependents.

The same is true for Lab. You have to fix a white reference.

ICC fixed D50 as white reference for PCS (Profile Connection Space, XYZ or Lab).

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Why not use Prophoto RGB (D65)? It can have all of Adobe RGB (D65) contained within
.
No difference all adobe RGB colors are contained in ProPhoto (D50 white reference).

David Coffin dcraw can output data in ProPhoto (D65). I don't investigate the reason, may be it was more simple. But there is no any difference in color management results.



Jacopo
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #316 on: January 05, 2011, 04:32:46 pm »

I was not thinking in terms of profiles when I wrote that. I was thinking of a standard definition of a linear color space that I have given before. Human vision is considered to have 3 dimensions, so it is a 3D space. The 4th vector (white point) is there to set units.
how could I create this colour space (i.e. the wirframe; white = ProPhoto)?
I could apply even more saturation but then the white point would start to shift towards yellow/red.

http://www.luminous-landscape.com/forum/index.php?action=dlattach;topic=49940.0;attach=35168;image
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #317 on: January 05, 2011, 04:35:55 pm »

how could I create this colour space (i.e. the wirframe; white = ProPhoto)?
I could apply even more saturation but then the white point would start to shift towards yellow/red.

http://www.luminous-landscape.com/forum/index.php?action=dlattach;topic=49940.0;attach=35168;image

Isn't it the same image we saw before which was a union of two different color spaces? May be I don't remember exactly. I need to go back and search for that message.

Joofa
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #318 on: January 05, 2011, 04:38:05 pm »

Isn't it the same image we saw before which was a union of two different color spaces? May be I don't remember exactly. I need to go back and search for that message.
no. It's one single colour space. But table based, not matrix based.
And it is a color space... you could actually use it.
You won't ... but you could.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #319 on: January 05, 2011, 04:39:33 pm »

no. It's one single colour space. But table based, not matrix based.
And it is a color space... you could actually use it.
You won't ... but you could.

So what is the point?
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