There is provided an adjustment method including, identifying correspondence between a projector coordinate system and a camera coordinate system, detecting brightness of a first area of a second captured image and brightness of a second area of the second captured image, estimating a range of first brightness of a third area of a second image, estimating a range of second brightness of a fourth area of the second image, and adjusting brightness of a fifth area corresponding to the third area in a projection image projected from the projector so as to fall within the range of the first brightness and adjusting brightness of a sixth area corresponding to the fourth area in the projection image so as to fall within the range of the second brightness.