Intensity Control and Contrast Control are grayed out when the grayscale method is Default dither; they are enabled when any other dither is selected as the grayscale method.
Intensity Control can be used to increase or decrease the lightness of image and graphics in the output AFP docs.
Contrast Control can be used to increase or decrease the contrast of image and graphics in the output AFP docs.
In most cases the two values do not need to be adjusted.
