A technique based on cross-correlation to make spatial measurements of x-radiographed objects

A technique has been developed to make accurate spatial measurements of the internal parts of objects from the digitized x-ray images of these objects. The technique involves the comparison of the x-ray image with each of a series of theoretical images which are produced by a computer model. When the theoretical image which best fits the actual image is found, the input parameters of the theoretical image are taken as estimates of the actual input parameters of the x-ray image.

The method used to compare the actual and theoretical images is based on the cross-correlation function. The cross-correlation function reveals the degree of similarity between the actual image and each of the theoretical images. The theoretical image yielding the highest correlation value is then the image which best fits the actual image.

The technique was tested by applying it to measure the inner hole radius of a hollow plastic cylinder. The cylinder was x-radiographed, and the image was digitized and analyzed. The analysis resulted in an estimate within 0.0005 cm of the machined radius of 1.7780 cm.