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Gamma correction with Upstart and a script

rated 0 times [ 0] [ 0] / answers: 1 / hits: 364 / 3 Years ago, sun, august 1, 2021, 2:34:22

I've written an Upstart job to automatically change display gamma according to change in display brightness:

start on (backlight-device-changed)

exec /usr/bin/gammach

And this is "gammach":

#! /bin/bash

Br=`cat /sys/class/backlight/acpi_video0/actual_brightness` # Display brightness

Gm=.$((((Br+76)%100)))                      # Corrected gamma according to brightness

xrandr --output LVDS --gamma $Gm:$Gm:$Gm

But every time i change brightness i receive this error in the log file:

Can't open display

I have tried xgamma, but received a similar error.

Any help appreciated. Thank you.

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answered 3 Years ago utilitere · Accepted Answer

I finally found the answer.

Apparently it was with permission and authorization to access Xserver and stuff like that.

The xgamma version of my script that works like a charm is:

#! /bin/bash

export XAUTHORITY=/home/<username>/.Xauthority  # This give permission to access Xserver

Br=`cat /sys/class/backlight/acpi_video0/actual_brightness` # Display brightness

Gm=.$((((Br+76)%100)))                      # Corrected gamma according to brightness

xgamma -d :0 -gamma $Gm