I am trying to find a way to control the apparent brightness of my external screen on Raspbian Stretch.

In my situation, there is no need to actually control the backlight, as I only want to change the apparent brightness.

On my desktop PC using Ubuntu, I can achieve this using xrandr:

$ xrandr --output HDMI1 --brightness 0.5

As the Raspberry Pi does not appear to be using xrandr by default, I am wondering of there is a way to enable it or if there is an alternative way of controlling the gamma/brightness value without the requirement to control the actual backlight of the screen.

The official HDMI configuration or Video options documentation does not seem to contain any such setting.

Any information that could be helpful here is very much appreciated!


xrandr is in the x11-xserver-utils package.

sudo apt install x11-xserver-utils

I haven't been able to test that it works, other than than it runs (and complains "Can't open display" for me; my Pi is headless).

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    I belive xrandr is installed by default on Raspbian, it does not seem to be used/supported by the proprietary VideoCore graphics driver though. So unless there is a way to make the driver use xrandr, I wonder how the brightness setting could be influenced any other way. – adriaano Mar 17 '19 at 15:05

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