An image display system that performs grayscale correction in accordance with the on-site environment, to display an image, is provided with: a calibration signal generation section (150) that generates calibration signals for displaying each of first and second grayscale correction images having two grayscale values of a single color, a color-light sensor (60) that measures luminance values under an ideal environment and the on-site environment for each of the first and the second grayscale correction images projected on a screen, a 1D-LUT generation section (140) that generates a 1D-LUT based on the luminance values measured by the color-light sensor (60), and a grayscale correction section (170) that stores the 1D-LUT generated by the 1D-LUT generation section (140) and performs grayscale correction.