img gamma

Gamma allows you to perform gamma correction on an image.

Automatically decides the “best” level to use by calculating. It finds the mean value for the image, then makes the mean value in the image half.
--by <n>
Amount to adjust the gamma level by. Gamma correction is defined by the power-law expression: $V^{1/n}$ for each colour channel value $V$.
Adjusts by the reciprocal of the value given to the --by flag, instead.