Brightness controls Gamma, not actual Brightness

In the modifiable options.txt file for Minecraft, Bedrock Edition in Windows 10 I noticed a strange attachment. The Brightness slider controls the GFX_GAMMA setting in the options.txt file? They are two different settings in a monitor/HDTV and should be two different settings in game. Standard Gamma for a video or a game application is 1 while standard Brightness is around 50 out of 100.