Image sequence based automatic multi-camera system calibration techniques

A fully automatic and rather flexible procedure for the calibration of stationary multi-camera systems for the 3-D observation of dynamic events is presented. While conventional close-range camera calibration techniques are either based on a stable pointfield with known reference coordinates or on a temporarily stationary pointfield with only approximately known 3-D coordinates, which is imaged from different locations and under different orientations with one single camera, the presented technique is based on stationary cameras and moving targets, making use of the image sequence acquisition nature of most solid state cameras. In the simplest version, only one single easily detectable marker has to be tracked through image sequences of multiple pre-calibrated cameras, thus avoiding the necessity of homologous feature identification for the establishment of multi-view correspondences; 3-D coordinates of the marker position are not required. This single-marker method does not allow for the determination of the interior orientation. In an extended version allowing for full camera orientation and calibration, a reference bar of known length is moved through object space, with the problem of feature identification and establishment of multi-view correspondences being reduced to the tracking of two targets. The method can only be used with multi-camera systems and is most useful for 3-D motion analysis applications, but may be adapted to a wide range of other applications. The advantages of the method over conventional self calibration techniques are the trivial establishment of multi-view correspondences, the fact that no temporarily stable target field has to be constructed, and the fact that each camera has to be set up only once. After the explanation of the technique, its theoretical performance is examined in detail based on extensive computer simulations, and the practical effectiveness is shown in a pilot study on industrial robot calibration. Based on these studies, recommendations are given concerning the number of reference bar locations, preferable reference bar orientation schemes and the achievable accuracy potential.