This script allows to change the gamma values like the script that ships with Poser, but is more user friendly (less clicking).
First select which item's (selected material only, the actors (and its figure's and the figure's parented/conformed items!) or all actors) materials and which material room inputs you want to change.
Then either press "reset" to set the gamma value to the render value or "set" to set the gamma to the value entered in the field "Gamma".