Arlen Heginbotham, BJ Farrar, Mark Erdmann
Abstract
X-radiography has been used since its invention to study works of art. X-rays of complex three-dimensional objects, such as sculpture, are notoriously difficult to interpret because the X-ray ‘flattens’ the object into two dimensions and there is no easy way to tell if an observed feature is near the front, middle, or back.
The advent of direct digital radiography (DR) has allowed x-ray images to be acquired more rapidly and efficiently than ever before. The availability of relatively inexpensive computer-controlled turntables for the photography market has precise and repeatable rotation of artworks in the X-ray studio. By placing sculptures on a turntable and making a series of high-resolution radiographs at pre-set intervals (typically 72 images at 5° intervals), we allow researchers and other viewers to see the entire sequence of images and freely ‘spin’ the objects in X-ray view. This helps tremendously in understanding complex internal structures. After radiography is complete, a digital camera can placed in the position of the X-ray source and photographs can be made at precisely the same intervals as the radiographs. This image set can be overlaid or placed side by side with the radiographs to further assist with interpretation of the radiographs.
Many sculptures or other 3D works of art are larger than a typical DR detector (14″x14″ or 11″x17″) We have designed and built a flexible and low-cost aluminum easel that allows the detector to be repositioned after each 360° rotation of the turntable. With the X-ray tube in the same position, the detector can be placed in an array of positions so that the entire object can be imaged in overlapping frames. For each detector position, the turntable rotates the subject through exactly the same series of positions, capturing an image at each. This process is easily automated using a two-monitor configuration for the control computer and simple task automation software. The resulting image sequences can be merged efficiently using movie editing software such as Adobe After Effects, yielding a single sequence of full-sized, high-resolution radiographs at regular angular increments.
Viewing and disseminating these radiography-in-the-round image sets presents certain challenges. Some product photography software can generate an interactive, browser-based viewer that allows the viewer to spin the image set and switch between X-ray and visible views but zooming can be awkward and slow refresh rate can be frustrating, particularly with large composite radiographs. A customized and optimized web-based viewer has been developed to overcome these obstacles and allow streamlined dissemination of radiography-in-the-round image sets.
Taken together, these developments should allow any museum radiography studio with a DR detector and an affordable automated turntable to capture, format, and disseminate their own radiography-in-the-round.