A calibration system includes an imaging device, an image forming apparatus, and a table generating unit. The table generating unit: calculates a first weighting coefficient based on dispersion of color values of pixels inside the patch in a captured image for each of the patches where the captured image is generated by simultaneously capturing the test chart of the sheet generated by the image forming apparatus and a preliminary prepared reference chart with the imaging device; calculates a representative value for each tone of the color value of each of the patches in the test chart and the reference chart based on an average of a weighted average of the color value of the plurality of patches; and generates the gamma correction table based on the respective representative values in the test chart and the reference chart.