Last month, during a discussion on Twitter with the GNU/Linux artist Tyson Tan, Neotheta and Wacom Official, I started to talk about the impossibility for GNU/Linux users to setup the brightness/contrast/RGB on their Cintiqs. And during this discussion Jason Gerecke -maintainer of the Linuxwacom driver- wrote a solution to this issue. Today, I'm reporting this solution on this article for better archiving and in the hope it will help future GNU/Linux artists at finding a solution to their problem.
About the issue:
Cintiqs are tablets made by Wacom with a display monitor built inside the surface of the pen tablet. In my carreer, I owned four Cintiqs. If you want to read my opinions about this tablets, read my full tablet history log article here. On the older models, the monitor had physical buttons to setup the brightness/contrast/RGB, something similar to many common monitors on the market. But around 2010, Wacom replaced the buttons by a driver (a software available only for Windows and Mac). That's why I never could manage to change the brightness and the contrast of my hardware. I had to use the default factory setting but this one was unfortunately too dark by default.
You need to open a terminal and install ddcutil. On my Kubuntu operating system, I install it with this line:
sudo apt install ddcutil
(Note: if you are new on GNU/Linux, use Ctrl+Shift+V to paste inside a terminal)
Getting the identifier of your Cintiq:
sudo modprobe i2c-dev
sudo ddcutil detect
Thanks to this two commands, you can list and get the identifier of the detected hardware by ddcutil. Unfortunately this two commands crashes my computer and freeze the display. I have to hard reboot holding the power button six seconds each time I'm using them. But the display freeze after printing the result on the screen and you'll have to run this commands only once to know your identifier. In my case, my Cintiq has a three letter capitalized identifier: WAC.
Listing the available settings:
sudo ddcutil --mfg=WAC capabilities
This command will list all the capabilities of the 'WAC' device (screenshot under). Each capabilities are identified by a number (eg. Brightness is number 10).
Knowing the current value of a setting:
To know the current intensity value of the brightness, you have to use 'getvcp 10' with this line:
sudo ddcutil --mfg=WAC getvcp 10
This command line output looks like that:
VCP code 0x10 (Brightness): current value = 50, max value = 100
Changing the value of a setting
Now if I want to switch the value of the brightness to 75%, I have to use 'setvcp 10' followed by 75:
sudo ddcutil --mfg=WAC setvcp 10 75
All other capabilities can be changed using setvcp. To change the color preset (14) to option 5 (6500K):
sudo ddcutil --mfg=WAC setvcp 14 05
Thanks to this control on the brightness/contrast/RGB of my Cintiq, I was able to match the same luminous intensity in cd/m² as my other monitors. I was also finally able to calibrate the Cintiq to sync with the colors of my other monitors. I also discovered it was possible to draw on this device during the day without having to close the windows and set my workplace into the dark. It was long, tedious to setup this device via the command line but it was possible. This totally made me focus back on digital drawing using this hardware. Thank you again Jason Gerecke for sharing this solution and obviously not thank you Wacom for publishing only drivers for Mac and Windows on your website. This story is just another proof that being an artist on GNU/Linux requires a lot of knowledge... or you might spend years of your life painting in the darkness (as I did).