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

[tgray]

Haha,  Iliah, I'd love to sit down with you one day and have a conversation.  You come across as an interesting guy on these forums.

[Graystar]

Bruce Lindbloom, the one expert that people seem to agree on is actually an expert, seems to back up what joofa is saying, with the limited set of conditions that agree with what joofa posited at the beginning.

Bruce Lindbloom did NOT back up what Joofa was saying.  He said...
"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."

Then he says...
"I believe that all of the reference RGB color systems share the basic premise that R=G=B is neutral."

And finally...
"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."

It’s crystal clear that this doesn’t support Joofa’s position.  What Lindbloom said is correct...if you perform Joofa’s color conversion of a neutral midtone, such as middle gray, then the result is not gray.  Joofa is taking one color, damaging it in the conversion, and then making claims about the damaged color.  The claims are true, but no one cares about damaged color conversions, as they serve no purpose.

[tgray]

Bruce Lindbloom did NOT back up what Joofa was saying.  He said...
"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."

I think that is the implication of not having the same illuminants, is it not?  Maybe joofa can and should answer this.

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

I think also that this is what Iliah was getting at with his examples of scenes with multiple illuminants. 

[Graystar]

I think that is the implication of not having the same illuminants, is it not?  Maybe joofa can and should answer this.

Or...or...how about this option...finish reading the Lindbloom quotes I provided.  The answer to your question is right there.

[tgray]

That's a useful approach to getting your point across.

[Graystar]

That's a useful approach to getting your point across.

Yes, I definitely agree that putting all the information required to answer your question into one post is a useful approach to getting my point across.

[MarkM]

Mark, I don't understand his point at all.  What on earth difference does it make that there is overlap in the spectral responses, as long as they are independent functions?

They are not independent functions—that's what he means. In a perfect world you could independently manipulate the individual cone type; you could find three wavelengths, one for each cone type and send light that would only stimulate each one. But it doesn't work because, with the exception of the far end of the red spectrum there are no wavelengths that only effect one cone. So when you use a green primary with the intention of manipulating the middle cone, you also inadvertently get some of the short cone or the long cone. It's not always a problem because you can often still find the right mix for a match, but for saturated colors it is a problem. He provides a real world example in the book with the calculations, which is convincing, but takes a few pages. (You might be able to find the pages in question by searching the book on Amazon of Google Books for the term: "Unwanted Stimulations" (A term I hear from wife from time to time)

[MarkM]

Yes, creating illusions is how it works, be it cartoons or fantasy. Chromatic adaptation can be viewed as creating an illusion, but used unproperly it destroys the illusion. Sometimes chromatic adaptation is for the sake of art, but sometimes it is just meaningless pseudo-physical accuracy and numbers.

That's an odd statement from someone who was recently preaching the merits of Mark Fairchild just a few posts ago.

Sensory chromatic adaptation is a real physical thing, not a parlor trick of color scientists. It's something we all know from experience and something that is easy to demonstrate experimentally.

From Fairchild's Color Appearance Models:

Perhaps the most important mechanism of chromatic adaptation is independent sensitivity changes in the photoreceptors…
Physiologically, changes in photoreceptor gain can be explained by pigment depletion at higher luminance levels. Light breaks down molecules of visual pigment (part of the process of phototransduction) and thus decreases the number of molecule available to produce further visual response…

Nobody is saying that the models for chromatic adaptation are perfect, or that there isn't also a cognitive aspect of adaptation, but when you are trying to accurately model color, an imperfect chromatic adaptation is better by orders of magnitude than no chromatic adaptation.

[Iliah]

> odd statement

What is odd in knowing that tools need to be applied adequately?

> Sensory chromatic adaptation is a real physical thing

Sensors are sensors. Sensory is sensory. Do you see blueish tint on a face of a human standing in a shadow? Sensors do, sensory - it depends.

[digitaldog]

Can't find HSL in Photoshop Info palette, sorry.

Ah, so you think that the naming in Photoshop means that the operation is based on the subjective human perception. Its not. See: http://www.crompton.com/wa3dsp/light/lumin.html and http://en.wikipedia.org/wiki/Brightness.

You are confusing Brightness (something we perceive) with Lightness (the L* in Lab) and assuming that the terms used in Photoshop accurately describe the differences (not so). Much like the Photoshop term Luminosity as in the "layer mode" called "luminosity" is not, it is actually calculating something like the "Luma" which is an old TV RGB transform. Luminosity is almost never the word you want unless your are trying  
to describe the total radiant energy (watts/sec) of a source, It has  nothing to do with what a human observer perceives. Brightness does.

[Iliah]

> you think that the naming in Photoshop means that the operation is based on the subjective human perception.

No I do not. And you know that I don't. It is just a name - brightness - that is historically used both ways. You know that, and you know that well. 

[digitaldog]

What's it telling about?

That he has not specified any practical use, nor any product or condition other than the hypothetical model he proposes that follows the hypothesis. As has been discussed ad nauseam, there is a reason for the adaptation and short of attempting to illustrate that ProPhoto RGB doesn’t fully contain Adobe RGB (1998), adaptation is used.

[digitaldog]

It’s crystal clear that this doesn’t support Joofa’s position.

Obviously we have our ideas of what we believe is correct here or this thread would have ended long ago. That said, what I read from Bruce’s comments fully agree with yours. Its interesting that some read it the other way. Considering what Bruce wrote, considering what the various utilities that plot gamuts, including Bruce’s show, considering that until I’m told otherwise, all applications TODAY that utilize these profiles follow the “logical” conversions Bruce recommends and some here have illustrated, its difficult for me to understand “the other sides” logic and persistence to accept their position.

[digitaldog]

It is just a name - brightness - that is historically used both ways. You know that, and you know that well. 

It may be used historically by some, its still an incorrect usage and the URL I posted explain the differences and why they should not be intermixed.

[MarkM]

You are confusing Brightness (something we perceive) with Lightness (the L* in Lab) a

Yes he is, and it's funny because he was so prepared to drop Mark Fairchild's name for no particular reason ("Fairchild, anybody") before he knew someone had his book on the nightstand. And it's funny because lightness and brightness are not just a names, they are fundamental concepts in color science, a field Iliah wants to assert some authority in. Authority begins with using terminology correctly. Fairchild devotes a chapter in his book to terminology. The CIE published The International Lighting Vocabulary decades ago. There is NO ambiguity here and there hasn't been for a long time.

[Iliah]

It may be used historically by some, its still an incorrect usage and the URL I posted explain the differences and why they should not be intermixed.

Please re-read what I typed referring to brightness. Scene is characterized by a range of brightnesses among other things. So we record brightnesses. How those brightnesses are coded in the capture is a different story.

By the way there is no point in discussing why Adobe are still preserving HSB, or wheter Adobe are "some", or "incorrect".

[Iliah]

> Yes he is

Well, you are not paying attention.

[broch]

> camera Yellow is not pure obviously.
Have you ever looked at some CFAs directly? In that case you might have seen that what is commonly called green component of a Bayer array is yellow in fact. And you somehow ignored "two different greens" problem, or are we back to dividing by zero and coming with 4=3?

CFA without green or red will not see yellow, dichromats see yellow as well as trichromats

[tgray]

Obviously we have our ideas of what we believe is correct here or this thread would have ended long ago. That said, what I read from Bruce’s comments fully agree with yours. Its interesting that some read it the other way. Considering what Bruce wrote, considering what the various utilities that plot gamuts, including Bruce’s show, considering that until I’m told otherwise, all applications TODAY that utilize these profiles follow the “logical” conversions Bruce recommends and some here have illustrated, its difficult for me to understand “the other sides” logic and persistence to accept their position.

Speaking to you and Graystar, I'm not disagreeing with you that the accepted way is the 'right' way to do things 99.9% of the time.  It makes sense; when we move from one color space to another, we want to preserve the appearance as much as possible most of the time.  That doesn't mean that joofa doesn't have a point and that considering it might lead to an interesting discussion of when it might be a good idea NOT to use chromatic adaptation during color space conversions.  I don't see this as a black and white scenario (pardon the pun).

And that's how I read Bruce's comment.  99% of the time,  AdobeRGB is fully contained in ProPhoto RGB.  However, if you do a certain thing which has some large consequences (R=G=B is not neutral), it's not.  That certain thing is the example that joofa pointed out.

[Iliah]

CFA without green or red will not see yellow, dichromats see yellow as well as trichromats

Try taking a shot through a colour separation red filter and you will see what I mean.