Canon EOS-1D X Manual (en)

Brightness: Move the slider to the right to make an image 
brighter and to the left to make an image darker.
Used to adjust modulation and degree of contrast 
of color. Move the slider to the right to make 
contrast of an image stronger and to the left to 
make contrast weaker.
The adjustment range is –100 to +100 (in 0.1-stop increments when 
entering a value).
You can adjust white balance using a selected part of an image as the 
standard for white to make the image appear natural. Using click white 
balance is effective when using it in parts of an image where white color 
tone has changed under the influence of a light source.
Click the [
] button.
Adjusting Color Tone Using Click White Balance