Spherically symmetric volume elements as basis functions for image reconstructions in computed laminography.Journal of Xray Science and Technology, :1-14
Abstract: Abstract Spherically symmetric volume elements (blobs) were evaluated as basis functions for iterative tomographic reconstructions in computed laminography. We implemented an iterative algorithm for the computation of three-dimensional reconstructions from computed laminography projections based on the simultaneous algebraic reconstruction technique also known as SART. Hereby, the discretization of the volume was realized by means of blobs based on generalized Kaiser-Bessel window functions. We found that band-limiting properties of blob functions are beneficial compared to a voxel basis particular in the case of noisy projections and if only a limited number of projections is available. In this case, using blob basis functions leads to sharper 3D datasets with less artifacts, which improves the capability to detect small features in images such as defects. The increased computational demand per iteration of the algorithm is compensated for by a faster convergence rate when using blobs, such that the overall performance of the tomographic reconstruction is approximately identical for blob as well as voxel basis functions. We conclude that despite the higher complexity, tomographic reconstruction from computed laminography data should be implemented using blob basis functions, especially if noisy data is expected.
Perception-driven Accelerated RenderingComputer Graphics Forum (Proceedings of Eurographics), 36
Abstract: Advances in computer graphics enable us to create digital images of astonishing complexity and realism. However, processing resources are still a limiting factor. Hence, many costly but desirable aspects of realism are often not accounted for, including global illumination, accurate depth of field and motion blur, spectral effects, etc. especially in real-time rendering. At the same time, there is a strong trend towards more pixels per display due to larger displays, higher pixel densities or larger fields of view. Further observable trends in current display technology include more bits per pixel (high dynamic range, wider color gamut/fidelity), increasing refresh rates (better motion depiction), and an increasing number of displayed views per pixel (stereo, multi-view, all the way to holographic or lightfield displays). These developments cause significant unsolved technical challenges due to aspects such as limited compute power and bandwidth. Fortunately, the human visual system has certain limitations, which mean that providing the highest possible visual quality is not always necessary. In this report, we present the key research and models that exploit the limitations of perception to tackle visual quality and workload alike. Moreover, we present the open problems and promising future research targeting the question of how we can minimize the effort to compute and display only the necessary pixels while still offering a user full visual experience.
Modelling and characterization of ductile fracture surface in Al-Si alloys by means of Voronoi tessellationMaterials Characterization,
Abstract: In this study, a new approach to model the system of dimples on the fracture surface of Al-Si alloys using the weighted Voronoi tessellation is proposed. The tessellation model is applied to metallographic images of the eutectic phase to simulate a fracture surface appearance (as projected on a fractograph) that would potentially exhibit this structure if it had been fractured under uniaxial tensile loading. It enables the determination of geometrical features of virtual fracture surface projections, such as the dimple density, the area and equivalent diameter distributions, and topographic features, such as the dimple depth, the surface area and the roughness, by means of geometrical approximations, empirical and analytical relations. A brief review of the fractographic observations on different Al-Si alloys is made to demonstrate preconditions and motivation for using mosaic methods and in particular their weighted version. The simulation results are confirmed by experimental measurements indicating the credibility and usefulness of the model. The routine for generating the weighted Voronoi diagram is implemented as a Java plugin for the Fiji interface and is easy to execute.
GPU Ray-tracing using Irregular GridsComputer Graphics Forum,
Abstract: We present a spatial index structure to accelerate ray tracing on GPUs. It is a flat, non-hierarchical spatial subdivision of the scene into axis aligned cells of varying size. In order to construct it, we first nest an octree into each cell of a uniform grid. We then apply two optimization passes to increase ray traversal performance: First, we reduce the expected cost for ray traversal by merging cells together. This adapts the structure to complex primitive distributions, solving the "teapot in a stadium" problem. Second, we decouple the cell boundaries used during traversal for rays entering and exiting a given cell. This allows us to extend the exiting boundaries over adjacent cells that are either empty or do not contain additional primitives. Now, exiting rays can skip empty space and avoid repeating intersection tests. Finally, we demonstrate that in addition to the fast ray traversal performance, the structure can be rebuilt efficiently in parallel, allowing for ray tracing dynamic scenes.