78 research outputs found
Improved Orientation Sampling for Indexing Diffraction Patterns of Polycrystalline Materials
Orientation mapping is a widely used technique for revealing the
microstructure of a polycrystalline sample. The crystalline orientation at each
point in the sample is determined by analysis of the diffraction pattern, a
process known as pattern indexing. A recent development in pattern indexing is
the use of a brute-force approach, whereby diffraction patterns are simulated
for a large number of crystalline orientations, and compared against the
experimentally observed diffraction pattern in order to determine the most
likely orientation. Whilst this method can robust identify orientations in the
presence of noise, it has very high computational requirements. In this
article, the computational burden is reduced by developing a method for
nearly-optimal sampling of orientations. By using the quaternion representation
of orientations, it is shown that the optimal sampling problem is equivalent to
that of optimally distributing points on a four-dimensional sphere. In doing
so, the number of orientation samples needed to achieve a indexing desired
accuracy is significantly reduced. Orientation sets at a range of sizes are
generated in this way for all Laue groups, and are made available online for
easy use.Comment: 11 pages, 7 figure
Multimodal Image Fusion and Its Applications.
Image fusion integrates different modality images to provide comprehensive information of the image content, increasing interpretation capabilities and producing more reliable results. There are several advantages of combining multi-modal images, including improving geometric corrections, complementing data for improved classification, and enhancing features for analysis...etc.
This thesis develops the image fusion idea in the context of two domains: material microscopy and biomedical imaging. The proposed methods include image modeling, image indexing, image segmentation, and image registration. The common theme behind all proposed methods is the use of complementary information from multi-modal images to achieve better registration, feature extraction, and detection performances.
In material microscopy, we propose an anomaly-driven image fusion framework to perform the task of material microscopy image analysis and anomaly detection. This framework is based on a probabilistic model that enables us to index, process and characterize the data with systematic and well-developed statistical tools. In biomedical imaging, we focus on the multi-modal registration problem for functional MRI (fMRI) brain images which improves the performance of brain activation detection.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120701/1/yuhuic_1.pd
Advancement and applications of the template matching approach to indexing electron backscatter patterns
Electron backscatter diffraction is a well-established characterisation technique used to determine the orientation and crystal phase of a crystalline material. A pattern is formed by dynamical interaction of elections with the crystal lattice, which can be understood and simulated by using Bloch wave theory. The conventional method of indexing a diffraction pattern is to use a Hough transform to convert the lines of the pattern to points that are easily accessible to a computer. As the bands of the pattern are direct projections of the crystal planes, the interplanar angles can then be computed and compared to a look up table to determine phase and orientation. This method works well for most examples, however, is not well suited to more complex unit cells, due to the fact it ignores more subtle features of the patterns. This thesis proposes a refined template matching approach which uses efficient pattern matching algorithms, such as those used in the field of computer vision, for phase determination and orientation analysis. This thesis introduces the method and demonstrates its efficacy, as well as introducing advanced methods for pseudosymmetry analysis and phase mapping. A new metric for phase confidence is also proposed and the refined method is shown to be able to correctly determine phases and pseudosymmetric orientations. Finally, preliminary work on a direct electron detector stage is presented. Work on the development, testing the pattern centre reliability, modulation transfer and an example map is shown.Open Acces
Global optimization for accurate determination of EBSD pattern centers
Accurate pattern center determination has long been a challenge for the
electron backscatter diffraction (EBSD) community and is becoming critically
accuracy-limiting for more recent advanced EBSD techniques. Here, we study the
parameter landscape over which a pattern center must be fitted in quantitative
detail and reveal that it is both sloppy and noisy, which limits the accuracy
to which pattern centers can be determined. To locate the global optimum in
this challenging landscape, we propose a combination of two approaches: the use
of a global search algorithm and averaging the results from multiple patterns.
We demonstrate the ability to accurately determine pattern centers of simulated
patterns, inclusive of effects of binning and noise on the error of the fitted
pattern center. We also demonstrate the ability of this method to accurately
detect changes in pattern center in an experimental dataset with noisy and
highly binned patterns. Source code for our pattern center fitting algorithm is
available online
Pattern Matching Analysis of Electron Backscatter Diffraction Patterns for Pattern Centre, Crystal Orientation and Absolute Elastic Strain Determination: Accuracy and Precision Assessment
Pattern matching between target electron backscatter patterns (EBSPs) and
dynamically simulated EBSPs was used to determine the pattern centre (PC) and
crystal orientation, using a global optimisation algorithm. Systematic analysis
of error and precision with this approach was carried out using dynamically
simulated target EBSPs with known PC positions and orientations. Results showed
that the error in determining the PC and orientation was < 10 of pattern
width and < 0.01{\deg} respectively for the undistorted full resolution images
(956x956 pixels). The introduction of noise, optical distortion and image
binning was shown to have some influence on the error although better angular
resolution was achieved with the pattern matching than using conventional Hough
transform-based analysis. The accuracy of PC determination for the experimental
case was explored using the High Resolution (HR-) EBSD method but using
dynamically simulated EBSP as the reference pattern. This was demonstrated
through a sample rotation experiment and strain analysis around an indent in
interstitial free steel
Diffractive triangulation of radiative point sources
We describe a general method to determine the location of a point source of waves relative to a twodimensional
single-crystalline active pixel detector. Based on the inherent structural sensitivity of
crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the
location of a wave emitter. The principle described here can be applied to various types of waves,
provided that the detector elements are suitably structured. As a prototypical practical application of
the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons
for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach
provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of
microstructural crystal orientations, strains, and phase distributions
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