DISPLACEMENT MEASURING METHOD AND DISPLACEMENT MEASURING APPARATUS

PROBLEM TO BE SOLVED: To provide a displacement measuring method and a displacement measuring apparatus in which accuracy of displacement measurement is improved by performing centroid position calculation without being influenced by a pixel having particular luminance.SOLUTION: A displacement measuring apparatus comprises a slit light irradiation device 2 which irradiates a measurement subject 1 with slit light 3, a camera 5 which images a photo cutting line 4 generated by irradiating the measurement subject 1 with the slit light 3, and an image processing device 7 which determines displacement of the measurement subject 1 from a photo cutting line image captured by the camera 5. In the image processing device 7, luminance of pixels in a centroid position calculation direction of the photo cutting line image captured by the camera 5 is approximated to ideal luminance distribution according to the least square method and further approximated again to the ideal luminance distribution according to the weighted least square method using a differential between a luminance value and an approximation value, and a centroid position of the photo cutting line image is calculated from an expectation value of that distribution, thereby determining the displacement of the measurement subject 1.