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Calibration of non-conventional imaging systems

This thesis investigates the calibration of cameras that do not conform to the standard pinhole-plus-distortion camera model. The ability to calibrate such camera systems is essential for the development of new, non-conventional, camera types. The major contributions of the thesis are the development of calibration algorithms for both central catadioptric cameras and non-central flexible mirror imaging systems. A key link between the calibrations of pinhole cameras and of general central cameras is expounded, upon which the proposed central calibration scheme is built. The proposed scheme incorporates constraints inherent to the geometry of central cameras, resulting in a method that is shown through rigorous experimentation to have superior performance to the standard generic method. An enabler for this calibration scheme is the use of active calibration grids, using structured light techniques, in place of standard calibration targets. An implementation and thorough characterisation of these active grids is presented. Nevertheless, the extraction of static calibration grid feature points from images with large distortions is still fundamentally important, in particular for experimentation with real images. To this end, a novel algorithm for the detection and consistent ordering of corners in such images of chessboard calibration grids is presented, and its capabilities are demonstrated. The flexible mirror imaging system investigated in this thesis consists of a fixed perspective camera viewing a deformable mirrored surface, which in general results in a non-central imager. A novel calibration technique is proposed that can model the flexibility of these systems, resulting in a calibration that is dynamically updated as the reflective surface flexes. Comprehensive testing for both constrained and unconstrained mirror deflections demonstrates that good calibration results can be obtained using this technique. Results for structure-from-motion and object reconstruction from a sequence of images from a calibrated flexible mirror camera are presented, establishing the capabilities of such calibrated non-conventional imaging systems.