You should be able to see each of the 20 individual sections in the gamma bar. If you can't, set your monitor's
contrast to 100% and then adjust the brightness until you can just distinguish each section (including the darkest
zone on the left). Doing so should allow you to view the pictures with optimal contrast and brightness.

Your monitor should be on for, at least, 30 minutes before you adjust the settings, and preferably with no bright
light shining on the screen.