Confusion on color profiles


(Matteo Bertolino) #1

Hi there.

I’m a little confused on how darktable works with color profiles. I am kind of a new user, but willing to keep going given the amazing results.
I refer specifically to screen settings, I attach the screenshot. 24

I must specify I have a Eizo monitor with its own specific color profile, with internal calibration software, RGB gamut.
Now, which settings would be the appropriate given the above, so to display images properly? Shall I select RGB for the display, or the “system display profile”? The funny things, this latter is also a RGB profile, yet it gives me very different results than if I apply RGB within darktable.

Many thanks in advance.

M.


#2

See: https://www.darktable.org/usermanual/en/darkroom_bottom_panel.html#softproof.


(Matteo Bertolino) #3

Thanks. I had gone through that previously.
Nevertheless, it does not explain my RGB issue, if I chose “system display” - as suggested by the manual in my case given my calibrated RGB monitor, I get different results than if I choose “RGB” from the menu “Adobe RGB”.
I must be missing something.


(Elle Stone) #4

I don’t know what you mean by “RGB” from the menu “Adobe RGB”. Is there a darktable menu named “Adobe RGB”, in which “RGB” is one of the available choices? I do use darktable from time to time, but I don’t recall seeing what you seem to be describing.

Is your “Eizo monitor with its own specific color profile” an actual ICC profile that is located on disk somewhere?

What operating system are you using? If Linux, then what software are you using to set the system monitor profile? Do you know what profile this software is actually setting as the system monitor profile?


(Matteo Bertolino) #5

I have a Mac.
I have my own .icc monitor profile generated by th internal Eizo software. I have access to the .icc profile, of course.
Yes, in darktable, as the image firstly attached shows, you have different display option.
Let me attach you another view, more complete:

27

Note the profile “Adobe RGB (compatible)”

Thanks.
M.


#6

IIRC on Mac the display is limited to sRGB. That’s a hard limitation coming from Gtk, cairo or OSX (I can’t remember). So I would guess that the system profile gives the same result as sRGB.


(Matteo Bertolino) #8

Very interesting.
Does that mean that I am stuck to sRGB profile when seeing my images? Having an RGB monitor??
What if I select RGB, and not “display profile”?
Indeed, as you suggest, when I choose “display profile” I get similar output as sRGB.

Thanks.


(Elle Stone) #9

Hmm, what you are showing is just the list of profiles supplied by darktable, plus the system monitor profile. You’d have to put a copy of your actual monitor profile in a folder where darktable can find it. My apologies, I know the location on Linux, but not on Mac.

On Mac, as @houz commented, the system monitor profile is probably sRGB. @Carmelo_DrRaw - can you confirm? I think you were looking into this problem at one point, yes? Is this problem “general” or just confined to gtk apps?

As an aside, as far as I know all monitors have “RGB” profiles - they all use additive color mixing to make different colors. So specifying “RGB” isn’t enough to narrow things down to a specific monitor profile. For example sRGB is an RGB profile.

Choosing AdobeRGB as the monitor profile isn’t the right choice unless the Eizo is actually calibrated to AdobeRGB - “whatever % coverage” of AdobeRGB isn’t the same as “calibrated to AdobeRGB”.


(Matteo Bertolino) #10

Thanks for your reply.
Mac is the operating system, but I use a different monitor. Yes, it’s an Eizo full RGB profile, it is not sRGB. I attach the specific color profile, if of any help.
It is calibrated through external profiler (i1Pro) via internal monitor’s software.
So, I guess my choice is indeed to choose Adobe RGB color profile as working profile.
Alternatively, how could I make darktable read my .icc attached??

Thanks.
CS2420(36884057)00000002.icc (3.7 KB)


#11

I still have no idea what you mean when you say “RGB”.

Go to https://www.darktable.org/usermanual/en/lighttable_chapter.html#lighttable_overview and look for setting the display color profile.

https://bugzilla.gnome.org/show_bug.cgi?id=681784#c12 might explain some more details.


(Carmelo Dr Raw) #12

Indeed, this is some kind of limitation of GTK apps. More precisely, in cairo-quartz-surface.c it is assumed that the input data is in sRGB format, and the transform to the display ICC profile is handled by Cairo itself. As a consequence, any application using Cairo for display output is forced to convert the pixels to sRGB in order to get correct, but gamut-limited, colors.

For my OSX packages I am patching Cairo to bypass this limitation. The trick is simple: I am “fooling” Cairo to believe that the display profile is sRGB, so that it performs an identity conversion… this way, I can directly output pixel values in the display colorspace.


(Elle Stone) #13

Hmm, checking the Eizo RGB XYZ values against AdobeRGB XYZ values, they really aren’t all that close, so I don’t think AdobeRGB would make a good substitute for an actual monitor profile:

rXYZ
eizo:     X="0.62322998" Y="0.27453613" Z="0.00166321"
adobeRGB: X="0.60974121" Y="0.31111145" Z="0.01947021

gXYZ
eizo:     X="0.19964600" Y="0.68313599" Z="0.06350708"
adobeRGB: X="0.20527649" Y="0.62567139" Z="0.06086731"

bXYZ
eizo:     X="0.14131165" Y="0.04232788" Z="0.75971985"
adobeRGB: X="0.14918518" Y="0.06321716" Z="0.74456787"

Though perhaps on the xy plane xy values might be fairly close. If you are curious, see @ggbutcher 's xy plotter: xyY Horseshoe Plotter

Anyway, here’s a screenshot from darktable, from the Lightroom tab:
dt-display-profile
See where it says “display profile” In Linux, hovering over those words shows you where darktable looks for display profiles. I don’t know about Mac.

Is “full RGB profile” perhaps an Eizo marketing phrase? I don’t think this phrase has any technical meaning.


#14

@Matteo_Bertolino Yes, that is the first thing I would try to do; i.e., drop your screen’s profile in one of the directories listed in the tool tip when you hover over “display profile”.


(Glenn Butcher) #15

Here’s the plot:

ezio-adobergb

and, the input XYZs in exiftool output format:

RedMatrixColumn: 0.62322998 0.27453613 0.00166321
GreenMatrixColumn: 0.19964600 0.68313599 0.06350708
BlueMatrixColumn: 0.14131165 0.04232788 0.75971985
FileName: ezio

RedMatrixColumn: 0.60974121 0.31111145 0.01947021
GreenMatrixColumn: 0.20527649 0.62567139 0.06086731
BlueMatrixColumn: 0.14918518 0.06321716 0.74456787
FileName: adobeRGB

That was fun… :slight_smile:


(Elle Stone) #16

Hi @ggbutcher - Nice plots!

That Eizo monitor profile seems to include all of AdobeRGB and then a fair bit more.


(Matteo Bertolino) #17

Hey!
Interesting indeed. But does that mean my Eizo has more gamut than Adobe RGB?? Sounds weird. It should, at best, be equal.

Now, either I find where to put my .icc color profile so that darktable can find it (anyone??), or I am better off choosing directly Adobe RGB from the given options.

Do you agree?

Thanks.


(Matteo Bertolino) #18

Reading here and there I found this, where the profiles should be places:

~/.config/darktable/color/in

the problem is having a Mac; I cannot find such folder with darktable icc profiles! The only darktable folders I found (thanks to this forum!) are the ones I attach.

Now, I even tried creating a new folder inside, called “color”, and another, called “in”, I places the .icc profile inside but, obviously, nothing, darktable does not see it.

Thanks.


(Christian Kanzian) #19

You are on the right path and you have to create the folders if they do not exist. But the manual as link by @houz says you need to place profiles for the monitor into the folder out not in.

So it should be:
~/.config/darktable/color/out


(Alberto) #20

Hi,

Not really. If I understand correctly the info given at the link above, and if darktable works like RawTherapee in this respect, then you should use “system display profile”, and tell the OS to use your icc profile (I don’t know how to do that on a mac, sorry).
You will not benefit from the wide gamut of your display unfortunately (the output will be clipped to sRGB), but at least you should see the “proper” colors (proper meaning as specified by your display profile).

I hope this is right, but I’m confident someone will correct me otherwise :slight_smile:


(Matteo Bertolino) #21

In a way, and given the above insights given by others, if darktable automatically converts everything to sRGB then any attempt of mine to install my .icc profile is useless.
If it was really so, welcome to another huge deficiency of the software. I feel.
I mean, come on, how can you not allow the software (a supposedly professional retouching program) to read a RGB profile?
This throws huge shadows on my ideas of switching from other software.
I really hope I am missing something…

Thanks.