The present invention relates to a gamma data generation method of a display device. In the method, gamma data including red gamma data, green gamma data, and blue gamma data is determined. A target luminance and a target color coordinate of a first reference gray are determined. Then, an image is displayed on a display device based on red, green, and blue input image signals for a first reference gray, and a first luminance and a first color coordinate from the image are measured. Then, it is determined whether a coordinate difference between the first color coordinate and the target color coordinate and a luminance difference between the first luminance and the target luminance are in an allowable error range or not. The first luminance and the first color coordinate are converted to a first coordinate of a CIE XYZ coordinate system, and the target luminance and the target color coordinate are converted to a target coordinate of the CIE XYZ coordinate system if the coordinate difference and the luminance difference are not in the allowable error range. Finally, the red gamma data, the green gamma data, or the blue gamma data is corrected so that a red luminance, a green luminance, or a blue luminance of the image is changed according to a comparison of the first coordinate of the CIE XYZ coordinate system with the target coordinate of the CIE XYZ coordinate system.