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

[bjanes]

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

Hmmm.......

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 physicsts?

Sir Issac Newton, possibly matched only by Einstein in his contributions to physics, made seminal investigations into color. Also controversy is not new in the field. See this article on Zur Farbenlehre. Newton was more concerned with the physical measurement of color whereas Goethe was more concerned with the perception of color. What's new under the sun?

Regards,

Bill

[tho_mas]

So what is the point?

... why not use a D50 colour space large enough to contain all the colours a camera can capture potentially...

http://www.luminous-landscape.com/forum/index.php?topic=49940.msg413205#msg413205

[joofa]

... why not use a D50 colour space large enough to contain all the colours a camera can capture potentially...

http://www.luminous-landscape.com/forum/index.php?topic=49940.msg413205#msg413205

I still don't see where you are getting at? You already have a linear XYZ color space that contains all of the colors that you can see.

Joofa

[joofa]

If you change the white reference, the matrices reflect this change.

But I thought you said that changing white point does not change anything?

No difference all adobe RGB colors are contained in ProPhoto (D50 white reference).

I thought with the wonderful graphs presented it has been established that Adobe RGB (D65) is not fully contained within Prophoto RGB (D50). Were you paying attention?

Joofa

[fdisilvestro]

There is a color space that is a lot larger than ProPhotoRGB, It is called DCam 5, developed by Joseph Holmes.
It is so huge that covers all visible colors. To achieve this, he uses a blue primary with negative coordinates.

http://www.josephholmes.com/propages/gamuts/DCam5.jpg

Scroll down this page until "7)DCam 5, J. Holmes" for a description

I don't have personal experience with it, but is surely looks interesting.

[jbrembat]

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

ProPhoto try to maximize the coverage of visible gamut. To do that imaginary primary are defined.
The problem is that the visible gamut is not a triangle. So something cannot be covered.
In any case natural colors are generally covered.

ICC was trying to solve a similar problem in ICC v4.
In this case the aim is to define a gamut that includes all the rendering device,specially printers.
But ICC v4 is not diffused and, in my opinion (but Greame Gill,author of Argyll, thinks the same),it's not very good for other things.

Jacopo

[tho_mas]

I still don't see where you are getting at? You already have a linear XYZ color space that contains all of the colors that you can see.

then I don't understand why you suggested to use a ProPhoto/D65
http://www.luminous-landscape.com/forum/index.php?topic=49940.msg413196#msg413196
never mind...

[joofa]

then I don't understand why you suggested to use a ProPhoto/D65
http://www.luminous-landscape.com/forum/index.php?topic=49940.msg413196#msg413196

Oh, that one. I suggested that in reference to all of so much talk about Adobe RGB (D65) and Prophoto RGB (D50). When I did my calculations I noticed that when I changed Prophoto RGB from D50->D65, the red and green primaries unit stimuluses did not bump a whole lot and apparently only the blue primary readjusted in a way that Adobe RGB (D65) was neatly contained in it. So I thought it was a natural container for all of those Adobe RGB (D65) blue to white shades that fall outside Prophoto RGB (D50).

Sincerely,

Joofa

[jbrembat]

But I thought you said that changing white point does not change anything?

I'm a little tired to explain the same thing.
I said:
you have to change white point from source color space to target color space to preserve colors.

I thought with the wonderful graphs presented it has been established that Adobe RGB (D65) is not fully contained within Prophoto RGB (D50). Were you paying attention?

Adobe RGB color space is contained in ProPhoto color space.
You can build wrong graphs as you can build wrong numbers.
If you use the correct way to go from a source color space to a target color space, you get the answers.
I tried to explain how a RGB color space is builded. If you don't understand, please read some book or surf the web.

Jacopo

[joofa]

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

Hi Peter,

This whole discussion started from a comment of Bill (BJanes) when he said something about gamuts. I was intrigued to investigate Prophoto RGB and Adobe RGB gamuts and presented my findings with 4 cases. If you remember even the title of my original note on DPRview was "When is ProPhoto RGB gamut bigger than Adobe RGB?" Please notice the word "When" as I presented 4 cases I found interesting. I thought it will be an interesting topic for LL and DPReview communities.

But I was not prepared for the personal attacks.

I am not a professional photographer and I am not ashamed to admit that I don't understand many of the tools used in commercial photography world because I don't use them. I don't even understand all of the lingo associated with them. All of the graphs and other things I did was based upon starting from elementary data regarding Adobe and Prophoto RGB spaces on Wikipedia and I plotted them by hand. However, this weakness of mine was attacked ferociously by many to indicate that I don't want to use certain tools.

I have studied color science and use some advanced topics in a very restrictive domain that does not match with commercial photographers.

So when I ask questions like "Why don't you use Prophoto RGB (D65)?" it is actually not criticizing anybody but I wanted to learn that what stops a professional photographer from using such stuff by slight alteration to standardized parameters.

Hope that helps.

Best regards,

Joofa

[Schewe]

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

And exactly how would you get an image into ProPhoto RGB D65? You can't get it inside of Camera Raw or Lightroom because they use an internal ProPhoto RGB color and a linear gamma. The white point is D50. So, you would have to do so using a color transform which as we already discovered does a chromatic adaptation. What would be the point? You can already contain all of Adobe RGB (1998) inside of ProPhoto RGB when you do a chromatic adaptation based color transform.

Maybe C1 could process into a ProPhoto RGB D65 profile but since we don't know the internal color space used by C1, we don't really know that ProPhoto RGB D65 would be any better or worse...

So, what raw processor could use ProPhoto RGB D65? If none could, the point is moot.

[Iliah]

> And exactly how would you get an image into ProPhoto RGB D65?

While it is not very relevant to the discussion, it is easily accomplished, even if converting through ACR/LR. Make a DNG and pre-process it before feeding to a converter.

[tho_mas]

ProPhoto try to maximize the coverage of visible gamut. To do that imaginary primary are defined.
The problem is that the visible gamut is not a triangle. So something cannot be covered.

but that is only a limitation of matrix based profiles.
attached (first attachment) the gamut of a (table based) profile I use mostly (colored; wireframe = ProPhoto; both D50). Actually it's smaller than ProPhoto... but the saturation in the bright blue and magenta exceeds ProPhoto.
Almost all "camera working spaces" in C1 exceed ProPhoto in the (bright) blue and/or magenta and/or cyan... while beeing somewhat smaller overall.

Maybe C1 could process into a ProPhoto RGB D65 profile but since we don't know the internal color space used by C1, we don't really know that ProPhoto RGB D65 would be any better or worse...

looking at the profile Phase provides for your P65 (second attachment) it covers a lot of blue and magenta not contained in ProPhoto (like all other camera profiles also the P65 profiles are D50).

[digitaldog]

Maybe C1 could process into a ProPhoto RGB D65 profile but since we don't know the internal color space used by C1, we don't really know that ProPhoto RGB D65 would be any better or worse...

And its entirely possible that the processing color space is quite different, maybe smaller than this variant of ProPhoto or even ProPhoto itself and either is only used as an encoding color space (convert and spit out data in this space).

One would also have to wonder, if a D65 variant of ProPhoto is so advantages, why didn’t Adobe utilize it? We have Melissa RGB, proving that Adobe isn’t shy about creating their own color spaces. If the ACR team (Thomas) really wanted a D65 variant or something with totally different, I’m sure he would have done so. The Kodak white papers discuss why they decided on a D50 WP. Some could debate their decisions were wrong.

[Peter_DL]

> 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?

yes please - could be a good starting point.
 
 

... If you remember even the title of my original note on DPRview was "When is ProPhoto RGB gamut bigger than Adobe RGB?" ...

Or the other way round: when is Adobe RGB gamut bigger than ProPhoto RGB ?
For me it is answered. Joofa, - many thanks for all the lessons learned here !
Let's move to the next question: when and where could it really matter ?
 
 

And exactly how would you get an image into ProPhotothe  RGB D65? You can't get it inside of Camera Raw or Lightroom because they use an internal ProPhoto RGB color and a linear gamma. The white point is D50...

So you're sure that Eric Chan ('madmanchan') couldn't place a different color space in the heart of ACR...
Of course aside from all restrictions of time, priorities in life, and possible sense of this excersise.
 
 
Peter
 
--

[Schewe]

So you're sure that Eric Chan ('madmanchan') couldn't place a different color space in the heart of ACR...

No, I'm quite sure he could (and would) if a strong use case could be made. So far I'm not convinced (I can't speak for him although I'll guarantee he's been lurking in this thread).

The one new color space I would like to have in ACR/LR is ProPhoto RGB colors and a linear gamma as an output space. This would allow some Photoshop work done in a ProPhoto RGB linear gamma (I do have a working space profile for that) without having to do a gamma correction to linear and back. Alas, Thomas Knoll said that was pointless since doing the gamma conversion to/from/to isn't very destructive.

You CAN do an export from Lightroom into arbitrary color spaces so one could go into a ProPhoto RGB D65 profile but considering the source processing is done based on D50, I'm not sure that would accomplish too much.

I'll have to take a look at C1 and see if outputting to ProPhoto RGB D65 offers anything...not sure it would. I'm not 100% sure the profiles for the P65+ are actual built profiles from the sensor or if they are arbitrary color spaces...I'll have to ask (and see if I can get permission to post it).

[Iliah]

> yes please - could be a good starting point.

Do you have a shot with a portrait in a shadow of tree and a  asphalt road lit by Sun? That would be a good starting point. Or a shot taken with a fill flash in a room lit by incandescent lamps? That would be a good starting point too.

[joofa]

Let's move to the next question: when and where could it really matter ?

What about multispectral imaging in a very narrow bandwidth around those non-overlapping gamuts?

Joofa

[tho_mas]

I'm not 100% sure the profiles for the P65+ are actual built profiles from the sensor or if they are arbitrary color spaces...

they are based on characterization data but further tweaked. So they do not represent all the colours a camera captures (they would be much larger then). Besides they are linearized and coded in Gamma 1.8. In a way they are the "ideal" individual working spaces for the respective cameras (I for one embed the camera profile on output and do all the further editing in Photoshop in that color sapce).
If you have a shot of a gretag macbeth chart and switch the "film curve" to "linear response" and set the input profile ("camera profile") to "no color correction" (or "color view", which is the same) and back to one of the approriate P65 profiles I think you pretty quickly understand how the camera profiles work.

[tgray]

Alas, Thomas Knoll said that was pointless since doing the gamma conversion to/from/to isn't very destructive.

It would be convenient if there was a simple to use interactive gamma adjustment accessible through layers in Photoshop.  Too bad the gray slider in levels has some aberration from a true gamma transformation... This guy talks about it here on page 19.  Instead we have to resort to doing it with color profiles or outside of Photoshop.