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