Wand-based Multiple Camera Studio Calibration

To meet the demands of the many emerging multiple camera studio systems in entertainment content production, a novel wand-based system is presented for calibration of both intrinsic (focal length,lens distortion) and extrinsic (position, orientation) parameters of multiple cameras. Full metric calibration is obtained solely from observations of a wand comprising two visible markers at a known fixed distance. It is not necessary for all cameras to see the wand simultaneously, cameras may face each other, and have non-overlapping fields of view. High accuracy is achieved by using iterative bundle adjustment of tracked feature points across multiple views to refine calibration parameters until re-projection errors are minimised over the required measurement volume. The approach involves a new automatic initialisation procedure and novel application of bundle adjustment to refine calibration estimates. Evaluation of wand-calibration is performed using an eight-camera system. Results demonstrate a reprojection error of approximately 0.5 pixels rms and 3D reconstruction error of less than 2mm rms for a capture volume of 2x3x2m. Advantages of wand-based calibration over conventional chart-based calibration include time-efficient calibration of multiple camera systems and calibration of camera configurations without all cameras having to view the same objects or having overlapping fields of view.