Moving the gamma and the brightness sliders does not do anything if I have set the Nvidia GPU in Nvidia X Server Settings, but they work with the Intel HD GPU. This is very annoying since I think the Intel HD GPU is a lot slower than the Nvidia one so I mostly use later, but if I want to play The Dark Mod (and I want to see the level (the default brightness and gamma is very dark)) I have to switch to the Intel HD GPU. What should I do to make the brightness and the gamma changeable with the Nvidia GPU. I am using Ubuntu 16.04, GeForce 820M/PCIe/SSE2(I guess).