Adjust brightness. Decreases or increases the image brightness.
Brightness adjustment (-100…+100 int).
Layer command. Applies to the current layer or to the composite image if
layer=comp. Ignored by effect layers. CMYK images or layers are converted to RGB before the operation is applied.
op_brightness=0, for no change of brightness.
Darken the background of an image slightly to emphasize the foreground content: