Computer Graphics World

July 2009 40 n n n n Digital Imaging Looking at a Prehistoric Star In all, 130-plus CR X-rays were taken of Leonardo, but the group needed a much clearer picture of those X-rays, and Tom Kaye was able to give the scientists just that. Kaye, an associate researcher with Burke Museum in Seattle, had a long his- tory of processing astronomical and micro- scopic images with advanced techniques and software similar to that used on the Hubble Telescope. Andersen and the team sent the foggy-looking X-rays to him, and he worked his digital magic, which he had done so often in the past on both galaxies and dinosaurs. "Leonardo was a few feet thick, and when you X-ray something like that, you have to hit him with a lot of X-rays to pen- etrate the subject. e problem is you lose detail in the image because of the bright X-ray source you are using. You end up getting an image that sort of looks like a cloudy blob," explains Kaye. "So the origi- nal images that came out of the X-ray pro- cess didn't show much detail." e group was looking to see if there were any details, such as internal organs, preserved inside the specimen. All they could see were faint hints as to what was inside. "e problem with the images was that a large portion of the dynamic range was taken up in these big, cloudy blobs," says Kaye. "e details were superimposed on these big curves of dark and light areas, and they were completely obscured. So my task was to selectively remove these large gradients in the image while preserving the small details." In a process that took more than a week, Kaye used several software tools to do a specific form of unsharp masking to cre- ate an even fuzzier image of the existing X-ray—one that has no detail, just the large gradient. en, he subtracted that re- sult from the original image. "So you are, in effect, taking out the rolling hills and valleys, and you are leaving the details of what is sitting on those hills and valleys on a flat plane," he explains. Next, Kaye leveled out the entire gra- dient, using software that is often used to remove the haze present in a fuzzy image of a galaxy to reveal stars. "It removes the fuzz and leaves the points of light," he says. In this case, after Kaye was done, what had been blurry little objects on the X-rays were now dinosaur ribs, for instance. e challenge for this evolutionary proj- ect resulted from the number of generated images, each of which had to be tweaked one at a time, pixel by pixel. en, each image had to be pieced together into a mo- saic, so that every image visually compared with those adjacent to it. At one point, Kaye and Andersen de- cided to try something unique and created some stereo imagery from the 2D X-rays. While at Houston, Andersen built a special gantry that allowed the group to change the angle of the X-rays to achieve 3D con- vergent stereo pairs. "Unfortunately, we didn't get enough of that done because each X-ray exposure took too long, and we couldn't produce enough pairs," says Kaye. However, the few that were available held promise for future applications in which CT scans are not possible. In the end, all the X-rays were aligned to show, for the first time, the internal struc- ture of a dinosaur—the leg bones, the head rolled over to the side, the neck, and the teeth. "You are looking at the dinosaur as he actually was in real life," says Kaye. "We mount these skeletons in museums, but that is usually our best interpretation of how they were. In this case, we could see the exact way nature had put him together." Kaye credits this accomplishment to computers and the latest advancements in image processing. He points out that the industry is making so many strides in digi- tal imaging that this type of work finally is available to others beyond NASA. "It's a very exciting time in this field," he adds. A Past Life So, what did the enhanced X-rays of Leon- ardo's insides reveal? "ere were several things we saw in the X-rays that gave us hints that maybe there were things pre- served inside the dinosaur," Kaye says. "It will take a little bit more technology to go in there and find out exactly what those things are, but certainly they did show there were structures inside the rib cage of the dinosaur that were preserved over many, many millions of years." After the X-ray enhancements, the scien- tists could clearly see how the skin laid on Leonardo's body. ey could see the orien- tation of his bones. "is is so rare," says Kaye. "One of the misconceptions people who are not in paleontology have is that every time a dinosaur skeleton is found, it Artist Joe Raffa generated this CG animated scene of Brachylophosaurs for a documentary about Leonardo titled Secrets of the Dinosaur Mummy. Image by Joe Raffa, Plastic Thought Studios.

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