Projective rectification from the fundamental matrix

This paper describes a direct, self-contained method for planar image rectification of stereo pairs. The method is based solely on an examination of the Fundamental matrix, where an improved method is given for the derivation of two projective transformations that horizontally align all the epipolar projections. A novel approach is proposed to uniquely optimise each transform in order to minimise perspective distortions. This ensures the rectified images resemble the original images as closely as possible. Detailed results show that the rectification precision exactly matches the estimation error of the Fundamental matrix. In tests the remaining perspective distortion offers on average less than one percent viewpoint distortion. Both these factors offer superior robustness and performance compared with existing techniques

Calibration and removal of lateral chromatic aberration in images

This paper addresses the problem of compensating for lateral chromatic aberration in digital images through colour plane realignment. Two main contributions are made: the derivation of a model for lateral chromatic aberration in images, and the subsequent calibration of this model from a single view of a chess pattern. These advances lead to a practical and accurate alternative for the compensation of lateral chromatic aberrations. Experimental results validate the proposed models and calibration algorithm. The effects of colour channel correlations resulting from the camera colour filter array interpolation is examined and found to have a negligible magnitude relative to the chromatic aberration. Results with real data show how the removal of lateral chromatic aberration significantly improves the colour quality of the image

China's Post Accession WTO Stance

We discuss China's stance in the WTO post-accession, noting the many issues with implementation of China's accession terms by 2007. We evaluate how much benefit China can realistically receive from WTO membership given current problems with dumping actions against China and trade restrictions against textile and apparel exports. We discuss emerging WTO and non-WTO trade disputes involving China, and China's now extensive regional trade initiatives which raise issues of multilateral regional balance on China's trade policy strategy.

Developing a Mammalian Behaviour Ontology

The use of the Entity + Quality (EQ) model in phenotypic descriptions is dependent on the use of specialised domain ontologies to define the entity under observation. A domain currently lacking a specialised ontology is mammalian behaviour, and so the Mammalian Behaviour Ontology is being constructed to address this. Top-level class distinctions are made between behavioural activities and behavioural functions of individuals, and those between two or more individuals. The ontology is manually developed and encourages contributions from domain experts

Towards dynamic camera calibration for constrained flexible mirror imaging

Flexible mirror imaging systems consisting of a perspective camera viewing a scene reflected in a flexible mirror can provide direct control over image field-of-view and resolution. However, calibration of such systems is difficult due to the vast range of possible mirror shapes and the flexible nature of the system. This paper proposes the fundamentals of a dynamic calibration approach for flexible mirror imaging systems by examining the constrained case of single dimensional flexing. The calibration process consists of an initial primary calibration stage followed by in-service dynamic calibration. Dynamic calibration uses a linear approximation to initialise a non-linear minimisation step, the result of which is the estimate of the mirror surface shape. The method is easier to implement than existing calibration methods for flexible mirror imagers, requiring only two images of a calibration grid for each dynamic calibration update. Experimental results with both simulated and real data are presented that demonstrate the capabilities of the proposed approach

Efficient generic calibration method for general cameras with single centre of projection

Generic camera calibration is a non-parametric calibration technique that is applicable to any type of vision sensor. However, the standard generic calibration method was developed with the goal of generality and it is therefore sub-optimal for the common case of cameras with a single centre of projection (e.g. pinhole, fisheye, hyperboloidal catadioptric). This paper proposes novel improvements to the standard generic calibration method for central cameras that reduce its complexity, and improve its accuracy and robustness. Improvements are achieved by taking advantage of the geometric constraints resulting from a single centre of projection. Input data for the algorithm is acquired using active grids, the performance of which is characterised. A new linear estimation stage to the generic algorithm is proposed incorporating classical pinhole calibration techniques, and it is shown to be significantly more accurate than the linear estimation stage of the standard method. A linear method for pose estimation is also proposed and evaluated against the existing polynomial method. Distortion correction and motion reconstruction experiments are conducted with real data for a hyperboloidal catadioptric sensor for both the standard and proposed methods. Results show the accuracy and robustness of the proposed method to be superior to those of the standard method

Which pattern? Biasing aspects of planar calibration patterns and detection methods

This paper provides a comparative study on the use of planar patterns in the generation of control points for camera calibration. This is an important but often neglected aspect in camera calibration. Two popular checkerboard and circular dot patterns are each examined with two detection strategies for invariance to the potential bias from projective transformations and nonlinear distortions. It is theoretically and experimentally shown that circular patterns can potentially be affected by both biasing sources. Guidelines are given to control such bias. In contrast, appropriate checkerboard detection is shown to be bias free. The findings have important implications for camera calibration, indicating that well accepted methods may give poorer results than necessary if applied naively

An integrated design towards the implementation of an autonomous mobile robot

This paper details the design and implementation of a wheeled mobile robot, which will be referred to as Mobius (Mobile Vision Autonomous System), for selfsustained indoor operation. Its rugged design enables it to be easily customised with auxiliary equipment providing a wide application base. This is facilitated by an accurately controlled high power drive system, with onboard power and computational sources, giving much improved performances and capabilities comparable to that of commercially available devices in the same price bracket. The mechanical and electrical design of the robot are presented, optimised for cost and performance. The remainder of the paper concentrates on the design and implementation of an accurate drive controlle

Modelling and removal of distortions in images

This thesis investigates the compensation and minimisation of distortions in images. Various forms of non-linear lens distortions are modelled and removed. Projective linear distortions are further minimised to give the closest ideal projection from erroneous cameras. Traditional camera calibration treats lens distortion simultaneously with camera pose and lens scaling factors. This often leads to complex algorithms with multi-image requirements, while alternative so called non-metric methods such as straight line techniques, lack ready usability and insufficient precision. Considering the calibration and compensation of non-idealitys separately, allows greater access to error free projections while considerably simplifying subsequent calibrations. The major contributions of this thesis are the precise calibration and removal of lens distortions and the minimisation of perspective distortions. A simple to use technique is proposed for the closed-form calibration of lens distortion based on a single view of a planar calibration chart. Detailed examinations show its accuracy and suitability for all levels of lens distortion. A related method is proposed for the removal of lateral chromatic aberrations in images. Distortion models and approximate inverses are derived to give precise accuracy over all distortion levels including fish-eye lenses. An analysis of calibration patterns is conducted to determine if the choice of pattern can influence the accuracy of the calibration. It is revealed that only specific patterns offer truly bias free control points. Distortion free images are optimally regenerated to minimise pixel scale distortions. This technique is further developed to uniquely minimise perspective distortions, with application to stereo rectification