Calibration

DispcalGUI is no longer in the Ubuntu repository as of Ubuntu 20.04. Mainly due to the absence of Python2 + some related packages.

Display calibration and profiling in Ubuntu using 'colormunki DISPLAY'

What software/hardware do I use ?

See here: Hardware and software

Basic commands.

Before starting the calibration/profiling, check if some basic commands work. At a command prompt type these commands:

• dispwin <enter> : this should display some color patches on your screen.

• colormgr get-devices <enter>: lists the devices in the colord database (probably there are no devices in the database currently).

How to calibrate and profile the display ?

Make sure that:

• Your screen-saver and display sleep timer is turned off. The upcoming tests run for a while and we do not want the screen to go to sleep in that time.

• Your display has reached its normal operating temperature. So have it powered on for at least 15-20 minutes before you start the calibration/profiling.

Then perform these steps to prepare the calibration/profiling:

1. Do a manual configuration of your display using the controls on your display (not using software that comes with the OS or with the video card). Use this web page to configure your display as good as you can. You have some 'initial' setup now. Also use the screen controls to set the color space (if that option is available). Mostly sRGB will do perfectly.

2. Now run dispcalGUI (you find it in the unity dash). DispcalGUI is a graphical front-end to Argyll.

   • First of all, click the little icon to make sure your 'Instrument' (x-rite ColorMunki DISPLAY in my case) is recognized:

I downloaded the 'Correction Matrix' for my measuring device/display combination from the Colorimeter Corrections Database . If there is no file for your measuring device/display combination, you can select 'Auto'.

• • Then click the 'Calibration' button near the top of the window. It brings you to the 'Calibration settings'. I have set the values as indicated below:

• Next, click the 'Profiling' button near the top of the window. I used the settings as indicated below:

• Now press the 'Calibrate & Profile' button near the bottom of the window. The 'measure area' window pops up.

• The idea is to click the 'Start measurement' button and then use the menu of your display to adjust the red, green and blue color channels as well as the brightness and end up with something like this:

• Click the 'Stop measurement' button and then the 'Continue on to calibration' button. This starts the calibration process (what else ...).

• • This process takes some time ... Once this has finished, dispcalGUI presents you with the question if you want to install the generated profile.

• • dispcalGUI now asks for some options to apply when installing the profile. I accepted the defaults to start with and clicked 'Install profile'.

  • Then it asks to start the import, click 'Import' (= runs the gcm-import command behind the scene).

• This ends the calibration and profiling part.

Where are the icc files now ?

DispcalGUI generates a *.cal and *.icc file (along with some scripts) in the directory $HOME/.local/share/dispcalGUI/storage/profile_name.

The generated *.icc file contains the calibration information to be loaded in the video card's LUT and the ICC profile data to be used by color managed applications (GIMP, UFRaw,...).

When you confirmed to install the generated profile for the current user only (see above), the *.icc file is copied into directory $HOME/.config/color/icc/devices/display .

If you ticked the 'System wide' radio button, the install copies the profile into /usr/share/color/icc .

The color.jcnf file

The 'Install profile' step above, also creates or updates a file called: $HOME/.config/color.jcnf . This is a JSON (readable text) file that maps the EDID of your screen to a profile and it is used for setting the X11 _ICC_PROFILE atom.

You can list its contents with the command: cat $HOME/.config/color.jcnf

The colord database mapping.db

The 'import' step above, copies the newly generated icc file into the $HOME/.local/share/icc directory and updates the colord database. The colord database is located here: /var/lib/colord/mapping.db .

To list its contents, type the command: colormgr get-devices

When I run this command on my system, I see this:

How gets the display calibration and icc profile loaded ?

When you open the 'Startup applications' icon in the unity dash, you will see that one of the commands to run at login is displaycal-apply-profiles. This command loads the videocard LUT and initialize the X11 _ICC_PROFILE atom with your icc profile. It knows which profile to use from the colord database (/var/lib/colord/mapping.db) and from $HOME/.config/color.jcnf.

So, applications (like GIMP and Digikam) which use the X11 _ICC_PROFILE atom should be able to find their way to our icc profile now.

Some other applications (like darktable) use colord to find out what icc profile to use.

For this, we need to add our new profile into the colord database.

How to add a profile to the colord database ?

To list the current contents of the colord database from the commandline, type this command at the command prompt:

colormgr get-devices

To manage the colrd database with a gui, use the "color" application from the dash.

Select you screen (Eizo-CS270 in my case) and click the 'Add profile' button, select the newly installed profile from the list and click 'Add'. Note that the profiles you see in the drop-down box when adding a profile are those present in $HOME/.local/share/icc and in /usr/share/color/icc ; it lists only profiles that are applicable ... display profiles in this case (not the printer profiles).

After adding you profile to the colord database, the result looks like this: