your browser window fill your whole screen to reduce the influence
of other images during this adjustment.
sure that you are running true color (either 24 bit or 32 bit)
This should look as smooth as possible from color to color.
your contrast as high as it will go while still being able to
tell the difference between color blocks 16 and 17. (this will
typically be all the way)
the brightness as low as possible while still being able to
see a difference between color blocks 1 and 2.
final step is to adjust your colour balance to get a neutral
grey without ANY colour cast in the grey blocks above.