1. A display system, comprising:a display device that transits from a power-off state to a power-on state; and
a brightness calculation device that calculates a brightness setting sequence based on a humidity amount over a first period in which the display device is in the power-off state, the brightness setting sequence being a sequence of a setting value of a brightness of the display device during a second period, the second period starting from when the display device transits to the power-on state, the setting value changing in time series,
wherein the display device displays an image signal at a brightness according to the brightness setting sequence,
wherein the brightness calculation device calculates, as the brightness setting sequence, a sequence in which the setting value gradually increases toward a prescribed expected value over a duration which is longer than a prescribed duration, in a case where the calculated humidity amount is greater than a prescribed threshold, and
wherein the brightness calculation device calculates, as the brightness setting sequence, a sequence in which the setting value gradually increases toward the prescribed expected value over a duration which is the prescribed duration or less in a case where the calculated humidity amount is the prescribed threshold or less.