The ftgamma demo program opens a window showing series of gray stripes filled with solid color and checkered pattern of pixels. Your monitor's gamma value roughly corresponds to the horizontal position where the solid and checkered stripes are equally bright when seen from some distance. Three brightness targets are explored: 33%, 50%, and 67%. If the input-output curve of your monitor does not follow ideal power law relationship, you might observe slightly different gamma values at different brightness levels. It is also possible to examine gamma values for basic colors.
Two alternative patterns relevant to font rendering are also provided, where slightly slanted lines are rendered using grayscale and subpixel anti-aliasing. In the grayscale case, the correct gamma helps to achieve uniform perceived thickness of the lines. The gamma value that corresponds to vanishing moiré pattern is ideal for anti-aliased font rendering. In the subpixel case, the correct gamma removes color fringes that remain even after LCD filtering.
This program does not have any options.
This program is part of the FreeType demos package.