Texture and Colour in Image Analysis

Research in colour and texture has experienced major changes in the last few years. This book presents some recent advances in the field, specifically in the theory and applications of colour texture analysis. This volume also features benchmarks, comparative evaluations and reviews

Numerically efficient algorithms for anisotropic scale and translation Tchebichef moment invariants

Anisotropic scale and translation invariants (ASTI) for Tchebichef moments have been proposed by Zhu et al. [27]. Since these invariants are derived via the decomposition of Tchebichef polynomials, it is unavoidable that the invariant algorithms inherit the complexities from the Tchebichef polynomials defined in terms of hypergeometric functions. Furthermore, in order to achieve anisotropic scale and translation invariance, the computation of translation invariants and scale invariants need to be performed sequentially. These have turned out to be the bottleneck for the invariant algorithms. Experimental results show that some of the computed ASTI features from symmetric patterns are less accurate. Thus, we would like to extend the work of Zhu et al. [27] to simplify the complexity of the algorithms and further improve the accuracy of the computed features. The three terms recurrence relation of the Tchebichef polynomials has been used to simplify and improve the computational efficiency of the invariant algorithms. Skew transformations are deployed to enhance the numerical accuracy of ASTI for Tchebhcief moments. Our studies show that the skewed features are less sensitive to noise and significantly enhance the accuracy of pattern recognition systems. This has been verified by the experiments on recognition of printed English letters and leaf patterns corrupted by noise and scaled and translated deformations. The simplification of the algorithms using the orthogonal property of basis functions also can be used to simplify more complex invariants like affine invariants of discrete Tchebichief moments. It can also be extended to derive invariants for other orthogonal based moments like Legendre moments, Krawtchouk moments, Hahn moments, etc

Full-field analysis of the dynamic behaviour of thermally stressed panels

This thesis details the research conducted over the course of three years under funding from the European Office of the United States Air Force (EOARD) and the Engineering and Physical Sciences Research Council (EPSRC) as a part of a long-standing effort to collect high-quality experimental data which can be used in the development and validation of predictive computational mechanics models. The focus of this study is on the acquisition of full-field displacement and temperature data when thermally and thermo-mechanically loading aerospace grade material panels as a means to study the effect of non-uniform temperature distributions on their dynamic behaviour at a component level (macroscale). The inclusion of this data in the development of a robust predictive model has also been investigated. To that end, a review of the existing literature is provided which highlights the current knowledge gaps in the modelling and experiments on the thermal and thermo-vibratory loading of panels, as well as the state-of-the-art in full-field data analysis. Initially, a finite element (FE) model was developed and compared to predictive and experimental data available in literature. This allowed for an investigation into the best practices to adopt in the development of a computational mechanics model with temperature-dependent material properties. It was found that a successful representation of experimental conditions strongly depends on the effective depiction of the thermal load and initial shape of the component. Then, a thin plate with free edges and constrained about its centre was heated using quartz lamps arranged in two different configurations and mechanically loaded using a shaker. Experimental modal analysis was used to acquire the resonant frequencies and mode shapes of the plate. Mode shapes were studied by exciting the plate to its first eleven resonant frequencies and acquiring displacement data using a Pulsed Laser Digital Image Correlation method (PL-DIC). Infra-red imaging was used to acquire temperature maps across the specimen. Experimentally-acquired temperature maps and measurements of the plate’s initial shape were included in a temperature-dependent FE model, developed according to the findings in the preliminary study, previously described. For the first time, experimental results showed the resonant response of the plate to strongly depend on the temperature distribution across the structure, correlating well with past predictive work in the literature. This was supported by the results from the finite element model, which were validated against experimental data and found to yield reliable predictions. The influence of temperature distribution in the deformation of panels was further investigated using a 1 mm plate with reinforced edges. The geometry was designed to emulate an aircraft’s skin with the reinforced edges performing the function of stringers and ribs. High temperatures were achieved using quartz lamps arranged in various configurations with controllable power output. PL-DIC was used to measure surface displacements and a commercially-available micro bolometer mapped the temperature distribution across the plate. Deflection results for the reinforced plate showed it to behave as a dynamic system that buckles out-of-plane when heated before relaxing to a steady state. It was demonstrated that the out-of-plane displacement experienced by the plate is strongly influenced by the in-plane spatial distribution of temperature