This is a nonlinear operation to lighten dark areas of the image.
When you enable the
GammaCorrection parameter, a gamma of 0.4 (= 1 / 2.5) is applied to the intensity image. The resulting data is scaled to preserve the original full-scale 16-bit image. The following formula illustrates this:
OUT = (216 - 1) * (IN / 216 ) ^ (1 / 2.5)