The Gamma page contains global preferences for the way your monitor displays colors
In this page you can set the way the program adjusts colors. Determining how the colors should be adjusted is done by using the three sliders and/or values.
There are four color sections, one for red, green, blue and gray each. Every section has an outer area and a center area. The outer area is a dithered pattern of pixels with luminance values of 0% and 100%, and the center area contains pixels with a luminance value of 50%. So to get correct values, the inner and outer area should be optically of the same intensity. Use the scrollbar and/or edit box to adjust the image's gamma level so that the inner areas and the outer areas are of equal brightness. The correction value that synchronizes their luminance is the gamma level of your monitor.