Gamma
Returns a new image with gamma correction applied to the red, green and blue channels. The alpha channel is left unchanged.
A gamma of 1.0 leaves the image unchanged. Values greater than 1.0 brighten the midtones,
and values below 1.0 darken them. Each channel value v in the range 0..255 is mapped
to 255 * (v / 255) ^ (1 / gamma).
image.gamma(2.0) // brighten the midtones
image.gamma(0.5) // darken the midtones
Note
For gamma correction as part of a filter pipeline in the scrimage-filters module,
see GammaFilter, which produces the same result.