img gamma

Gamma allows you to perform gamma correction on an image.

--auto

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 $V$.

--undo

Adjusts by the reciprocal of the value given to the --by flag, instead.