Comparative analysis of high velocity projectile images using MATLAB

The Materials Testing Facility (MTF) at the U.S. Naval Research Laboratory (NRL) routinely captures orthogonal x-ray images of launch packages (LP) as they travel through the flight tube after a launch. Located about a meter from the target plates, the x-ray images provide a useful diagnostic for determining the performance of the materials used during the test. The images are captured on digital image plates, a reusable technology that uses a laser to scan the photo-stimulated phosphor particles, thus rendering a digital image that can be processed by a computer software package. While the image alone is useful, it would be beneficial to have a detailed analysis of the LP captured in the x-ray image, such as a comparison between a pre-launch static image and the post-launch image to determine where damage has occurred and to what extent. The MATLAB script that was developed will calculate the area of the LP in both the test and original versions, and compare the two images. There are a number of technical challenges that were addressed to develop the analysis. Because the projectile is traveling at hypervelocity, it is difficult to obtain a clear image of the projectile, as the pixel intensity value, which measures the brightness of a pixel, only varies by a few intensity levels from that of the background. In addition, the location of the projectile on the image is always different, owing to variations in the velocity of the LP. To address these issues, a series of image enhancement routines were developed. The development of these techniques and user interaction scripts will be discussed in this paper.