ArmA 3 does not support HDR output although it has a very advanced lighting engine with high precision internal HDR rendering. I do not understand why they are unable to provide HDR output. It's a huge missed opportunity as this game could be a prime example of proper HDR lighting.
From complete darkness to bright sunlight, ArmA 3 has a very high luminosity range. The tonemapper then takes care to produce output for the 8-bit monitors. As compromises have to be made when lowering precision, this results in banding in the nightskies and black clamping looking at dark areas. HDR-capable monitors like OLEDs offer increased contrast and precision (10 bit) to mitigate these issues. The game should support this too.
I also created a ticket here: https://feedback.bistudio.com/T167971
I also saw pcgamingwiki mentioning the issue in the HDR section: https://www.pcgamingwiki.com/wiki/Arma_3#Video
Edit: I made the game run in HDR using SpecialK with the "remaster 8bit passes" option. However this only works by skipping the launcher and disabling Battleeye, so it's not a general solution and doesn't work in Multiplayer. I would love to show you a proof of the smooth sky gradient i got now, but i don't know where to upload .jxr images.
