R'G'B'

R'G'B' is gamma corrected RGB.

The gamma correction adjusts the overall brightness of an RGB image by normalizing the pixel's RGB color components from its current integer values of 0 through 255 to real numbers between 0.0 and 1.0.

It then raises the normalized value of the pixel to a specified power, which is otherwise known as the gamma value. It will then transform the new value back to an integer component between 0 a 255.

Any gamma value between 0 and 1 will lighten up an image while anything higher will darken the image.