System color profile leading to different RGB values?

I wanted to learn the channel mixer module in darktable with the help of a simple test picture with a black background and the different main color spots. Therefore I created such a picture in gimp.

Black background RGB 0 0 0, then red 255 0 0, green 0 255 0, blue 0 0 255 and some mixed colors.

As it turned out, in darktable analyzing the picture I did not get a black as expected.

Black turned out to be 13 14 14 and all the other colors had different too.

Long story short: I found out that this feature? is connected to my system color profile. When I switch to one of the other display profiles the RGB values are as expected.

It was just recently that I set up a color profile on my computer, i.e. I have little experience with it.

I presume that my color profile is somehow corrupt. Am I right? Does anyone have any idea how I can fix this? (I’m running Manjaro 18.1.5 with XFCE)

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Something wrong with your colour management?

Yes, I think you are right.
It seems to me that color management in linux is a really tricky issue.
Colord and xiccd daemons are running and the color profile is set.
darktable-cmstest states that there are different profiles used. But the profiles used are the same…

Might that error lead to such an effect? Any idea of how I can fix it?

I run i3 with xiccd as a user process and colord as a system service and my darktable-cmstest is OK.

Can you share that test image? Perhaps it’s an issue with Darktable or XFCE colour management? One of the reasons I changed to Cinnamon DE from XFCE is that cinnamon handles colour management very easily.

Of course can you have the test image. Thanks for the tip, next week I get a new computer, maybe I give cinnamon a try…

RGB_Test_Channel_Mixer.tif (8.0 MB)

I downloaded your tif, beautiful… :smiley:

Looking at the metadata with exiftool, the image doesn’t have an embedded profile, or any other tag that might be used to do a display conversion. So, asking darktable folk, does dt automatically assign sRGB to an input image if it doesn’t have an embedded profile? The color management needs an input profile to use in the conversion to display space…

I did not know that the icc profile can be included in the picture… Actually, I made that image on my laptop where I did not use any color management. That’s why there is no information included.

I just made a second version on my computer with the color management running.
I’ve done better this time, much more beautiful I would say :wink:

The icc information is included now.
Channel_Mixer_Test_W520.tif (8.7 MB)
The funny thing is that I was not able to draw the desired colors with RGB 255 0 0 for red for example. I added the correct RGB values in gimp, but red is now 243 14 11. Only black and white are as expected…
This is really weird, I think my color management is messed up completely…

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You could probably make a smaller simpler image and upload a XCF as well so we can see whether you did something unusual in GIMP.

I opened your first image with my hack software and turned off the color management display conversion, and all your values are as expected. The picture is fine…

I’m just wondering how darktable was able to make a display conversion without an embedded profile.

Hi Mica,
I had never heard of the i3-wm before. I played around with it last night. I gotta say I’m amazed! Very tidy, easy and straight forward.
Unfortunately, it doesn’t help my color management problem…

Last night I reinstalled my color management.
Unfortunately with the same result. I must have repeated my mistake…
I don’t question my profile. I think I have to solve a problem with my color management, i.e. xiccd or colord.

I did reset my color management:

[marco@W520 ~]$ xprop -display :0.0 -len 14 -root _ICC_PROFILE
_ICC_PROFILE: no such atom on any window.

On the weekend I will go through the whole process again. For that I will use this description:

Is it still up to date, or is there a more comprehensive description for setting up the color management under linux available?

@ggbutcher I’m not sure what to expect here, isn’t it that the colors are displayed adjusted according to the color profile used? Do I always need to embed the profile also in the picture?

I always make sure any JPEG, TIFF, or PNG I save has an embedded profile that represents the image’s colorspace. And, that colorspace is almost always sRGB; that’s for anyone who wants to look at it that doesn’t have color management, chances are their consumer display will be close to sRGB.

Just went back in the thread; thought I had posted this reference here but hadn’t:

I wrote this after trudging through just what you’re experiencing now. It might help you focus attention toward the thing that isn’t behaving…


It is a good habit to include the ICC profile; however, there is no guarantee that the app or renderer would honour or be able to read it; particularly, the PNG, even though the ICC chunk has been standard since 2004. In addition, it can be removed automatically by web apps and sites to save space or as a security measure.

So, I also convert the data to sRGB, though I know there are still many interpretations of it and many more environments that aren’t colour managed. We can only do so much! :see_no_evil:

Which version of XFCE are you running in Manjaro? 4.14 supports colour management. Are you using the colour management dialogue to apply the colour profiles to your monitor? xfce:xfce4-settings:4.14:color [Xfce Docs]

This is the colour management dialogue in Mint 19.3 XFCE, which uses XFCE 4.14 (although I’m currently running Mint 19.3 Cinnamon)

On Manjaro I had also running 4.14. I did not use that dialogue to activate it, but the information on it was the similar as on your screenshot…

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I also run xfce and face the same issue. x atom and colord have a profile with the same description but x atom shows _ICC_PROFILE whereas colord shows a path to the icc profile.

Do you also encounter the change of RGB values when switching the display profile?

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I’ve certainly noticed a change in the colours on that Channel_Mixer_Test_W520.tif , when I switch the display profile in Darktable from sRGB, to my calibrated monitor profile… Red is only 255,0,0 when I use the sRGB display profile in Darktable, otherwise it is something like 144,17,5 .

I have set my display profile using the gnome colour manager in Mint Cinnamon… So I’m also now confused!

I’d have though that the system display profile would only affect how the colours are displayed in the window manager, and not affect the actual RGB values of the image in for example Darktable. E.g. red would still be 255,0,0, even if the display profile swapped red & green over.