and the centroid position of the focal spot can be calculated by the
gray centroid method. We calculated the centroid position of the
focal spot by two-dimensional scanning. The two results are also
compared to verify the accuracy of the algorithm. In the measurement
process, on the purpose of reducing error, collected five
consecutive images in each position after moving, took the average
of five corresponding matrices after noise removal as the
measurement data.
The gray image of the focal spot from the data directly read
out by the CCD as shown in Fig. 6(a). The intensity distribution
obtained by Gaussian fitting is shown in Fig. 6(b). The centroid