Implementation of Efficient Pan-Tilt-Zoom Camera Calibration

Report No. ARL-TR-4799
Authors: Nicholas Fung and Philip David
Date/Pages: April 2009; 22 pages
Abstract: Pan-tilt-zoom (PTZ) cameras, frequently used in both online and automated surveillance applications, require accurate knowledge of camera parameters in order to accurately register autonomously tracked objects to a world model. Due to imprecision in the PTZ mechanism, these parameters cannot be obtained from PTZ control commands but must be calculated directly from camera imagery. This report describes the efforts to implement a real-time calibration system for a stationary PTZ camera. The approach continuously tracks distinctive image feature points from frame to frame, and from these correspondences, robustly calculates the homography transformation between frames. Camera internal parameters are then calculated from these homographies. Finally, the external parameters can be calculated from the internal parameters and image homographies. The calculations are performed by a self-contained program that continually monitors images collected by the camera as it performs pan, tilt, and zoom operations. The accuracy of the calculated calibration parameters are compared to ground truth data. The program works with a higher degree of accuracy for small changes in the camera's external parameters. In addition, long algorithm execution time prevents the algorithm from running under all real-time conditions.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2009