Wide Image Stitching Based on Software Exposure Compensation in Digital Radiography

We investigated a wide image stitching method in digital radiography where an X-ray tube is stationary while a detector moves from one exposure position to the next during acquisition of multiple images of a small field of view. This method completely emulates the common radiographic geometry and is free of the parallax artifacts inherent in the source-translation method, showing improved image quality with reduced geometric distortions. One difficulty associated with this method is that the exposure levels of the individual images vary according to the inverse square law of the X-ray intensity, which may result in heterogeneous stitched images. In this paper, we propose a new software exposure compensation (SEC) scheme able to overcome this difficulty, and in this study, we performed an experiment to demonstrate the feasibility of using the proposed SEC in wide stitching. Four X-ray images of a test phantom were obtained in different exposure positions and were intensity-compensated by using the SEC algorithm prior to phase-correlation-based registration and alpha blending. Our results indicate that the proposed SEC scheme effectively compensates for the exposure discrepancies of the individual images, and thereby homogeneous and seamless stitched images can be obtained with high accuracy in the wide stitching.