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This is my first post here. I'm at the beginning of the road called Raspberry Pi.

Is there any way of changing the gamma/contrast/brightness of monitor via Raspberry Pi?

My Samsung 960BF doesn't have any hardware adjustment, only a power button.

I tried using xbacklight and got error

"No outputs have backlight property".

gddccontrol also didn't work. Error:

I/O warning: failed to load external entity "/home/pi/.dccontrol/monitorlist"  
   Document not parsed successfully
   Probing for available monitors"

And nothing is happening.

I connected my monitor through DVI-HDMI cable. Maybe this is why it doesn't work?

I'm using Raspberry Pi B+ V1.2 with Raspbian.

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One tool I have used successfully (not on a pi though), is xcalib from the package of the same name. You can use it to change the gamma, eg:

xcalib -gc 1.1 -a

You can repeat this. To cancel use

xcalib -clear

Another useful option is making the whole screen reverse-video:

 xcalib -invert -a

It is intended to work with icc profiles, but I have only used the above commands.

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  • Thanks for reply. I tried this, but nothing happens, end after executing command: xcalib -b 99 there is an error: "Warning: Unable to read file ' ' "
    – tarzanno
    Jul 8, 2015 at 13:44
  • You would need -b 99 -a but I wouldnt do that, the screen will be all white.
    – meuh
    Jul 11, 2015 at 4:34
  • Unfortunately, it doesn't work either. I tried 'xcalib -b 99 -a', 'sudo xcalib -b 99 -a' , and 'xcalib -b 10 -a' to make sure my monitor is not set to max brightness already. There is no error and nothing is happening. I'm afraid that I will need to learn i2c and control the monitor by that...
    – tarzanno
    Jul 11, 2015 at 11:47
  • Perhaps your cable is not passing through the i2c data line. Look in your /var/log/Xorg.0.log or similar log file to see if the display's eeprom was found (look for EDID).
    – meuh
    Jul 11, 2015 at 12:12
  • Nothing like that exists in this file. There is only a line telling that Rpi is using default monitor and : "no device specified for default monitor section". Must I buy a new HDMI-DVI cable, or there is another way?
    – tarzanno
    Jul 11, 2015 at 12:31

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