Shane Latham

Optimal Gabor filters for textile flaw detection

Abstract The task of detecting flaws in woven textiles can be formulated as the problem of segmenting a “known” non-defective texture from an “unknown” defective texture. In order to discriminate defective texture pixels from non-defective texture pixels, optimal 2-D Gabor filters are designed such that, when applied to non-defective texture, the filter response maximises a Fisher cost function. A pixel of potentially flawed texture is classified as defective or non-defective based on the Gabor filter response at that pixel. The results of this optimised Gabor filter classification scheme are presented for 35 different flawed homogeneous textures. These results exhibit accurate flaw detection with low false alarm rate. Potentially, our novel optimised Gabor filter method could be applied to the more complicated problem of detecting flaws in jacquard textiles. This second and more difficult problem is also discussed, along with some preliminary results.

Digital rock physics: 3D imaging of core material and correlations to acoustic and flow properties

3D X-ray microtomographic imaging and visualization of core material at the pore scale and subsequent analysis of petrophysical properties can give important insight to understanding properties of reservoir core material. 3D images allow one to map in detail the pore and grain structure and interconnectivity of core material. Numerical calculations on image data are in agreement with experimental data for flow and elastic properties on simple core material. This development forms the basis for developing more meaningful structure-property correlations in rock.

Permeability Upscaling for Carbonates from the Pore-Scale Using Multi-Scale Xray-CT Images

bility due to large permeability contrasts. The most accurate upscaling technique is employing Darcy’s law. A key part of the study is the establishment of porosity transforms between highresolution and low-resolution images to arrive at a calibrated porosity map to constraint permeability estimates for the whole core.

A constrained minimisation approach to optimise Gabor filters for detecting flaws in woven textiles

Gabor filters have proved to be an effective segmentation and flaw detection tool. This study addresses the issue of an optimal 2-D Gabor filter design for automatically detecting defects in homogeneously textured woven fabrics. The parameters of these filters are derived through an optimisation process performing the minimisation of a Fisher cost function. By constraining some of the Gabor filter parameters to specific values the aim is to optimise the filter to detect a certain type of flaw as it appears in a particular textile background. To account for the potentially large variety of flaw types, the optimal parameters for multiple sets of constraints are computed. The detection outcomes from each set of optimal filters are combined to produce a final classification result. Successful detection results (with low false alarm rates) suggest that this optimal Gabor filter approach is a promising method for automated detection of flaws in homogenous textiles.

An auto-focus method for generating sharp 3D tomographic images

We present a simple, robust, and versatile solution to the problem of blurred tomographic images as a result of imperfect geometric hardware alignment. The necessary precision for the alignment between the various components of a tomographic instrument is in many cases technologically difficult to implement, or requires impractical stability. Misaligned projection sets are not self-consistent and give blurred tomographic reconstructions. We have developed an off-line software method that utilises a geometric model to parameterise the alignment, and an algorithm for determining the alignment parameter set that gives the sharpest tomogram. It is an adaptation of passive auto-focus methods that have been used to obtain sharp images in optical instruments for decades. To minimise computation time, the auto-focus strategy is a multi-scale iterative technique implemented on a selection of 2D cross-sections of the tomogram. For each cross-section, the sharpness is evaluated while scanning over various combinations of alignment parameters. The parameter set that maximises sharpness is used to reconstruct the 3D tomogram. To apply the corrections, the projection data are re-mapped, or the reconstruction algorithm is modified. The entire alignment process takes less time than that of a full-scale 3D reconstruction. It can in principle be applied to any cone or parallel beam CT with circular, helical, or more general trajectories. It can also be applied retrospectively to archived projection data without any additional information. This concept is fully tested and implemented for routine use in the ANU micro-CT reconstruction software suite and has made the entire reconstruction pipeline robust and autonomous.

Multi-resolution radiograph alignment for motion correction in x-ray micro-tomography

Achieving sub-micron resolution in lab-based micro-tomography is challenging due to the geometric instability of the imaging hardware (spot drift, stage precision, sample motion). These instabilities manifest themselves as a distortion or motion of the radiographs relative to the expected system geometry. When the hardware instabilities are small (several microns of absolute motion), the radiograph distortions are well approximated by shift and magnification of the image. In this paper we examine the use of re-projection alignment (RA) to estimate per-radiograph motions. Our simulation results evaluate how the convergence properties of RA vary with: motion-type (smooth versus random), trajectory (helical versus space-filling) and resolution. We demonstrate that RA convergence rate and accuracy, for the space-filling trajectory, is invariant with regard to the motion-type. In addition, for the space-filling trajectory, the per-projection motions can be estimated to less than 0.25 pixel mean absolute error by performing a single quarter-resolution RA iteration followed by a single half-resolution RA iteration. The direct impact is that, for the space-filling trajectory, we need only perform one RA iteration per resolution in our iterative multi-grid reconstruction (IMGR).We also give examples of the effectiveness of RA motion correction method applied to real double-helix and space-filling trajectory micro-CT data. For double-helix Katsevich filtered-back-projection reconstruction (≈2500x2500x5000 voxels), we use a multi-resolution RA method as a pre-processing step. For the space-filling iterative reconstruction (≈2000x2000x5400 voxels), RA is applied during the IMGR iterations.

Flaw detection in jacquard fabrics using Gabor filters

This work is a part of ongoing research in the area of automatic visual inspection systems for real-time detection of fabric defects. The study aims to extend and evaluate the application of the joint space/spatial-frequency approach represented by the use of Gabor elementary functions for inspecting intricate jacquard patterns. It assesses the utility of multiresolution properties of Gabor-filters and the need for adaptive selection and integration of appropriate resolution levels of the image pyramid. The choice of the appropriate levels takes into consideration characteristics of the potential defects.

Designing for Mixed Wettability

In this paper we describe a technique based on radio frequency plasma treatment in H2O vapour to reproducibly clean and modify the surface energy of clastic and carbonate core material allowing the establishment of well defined wettability conditions. We present micro-tomographic observations of the pore-scale fluid distributions in strongly water wet clastic and carbonate cores. We then establish mixed-wet states in the same cores using controlled hydrophobation. Micro-tomography is again used to reveal the three-dimensional geometry and topology of water and oil wet regions. The tomographic data shows that under water wet conditions at intermediate saturations larger pores are predominantly oil filled while smaller pores remain water wet. We perform displacement experiments using clastic and carbonate cores at well defined wettability conditions and report measurements of resistivity index. These methodologies may provide insight into the role of rock microstructure and surface energy variability in determining recovery and production characteristics of oil and gas reservoirs.

Dual-energy iterative reconstruction for material characterisation

In this paper, we develop a dual-energy ordered subsets convex method for transmission tomography based on material matching with a material dictionary. This reconstruction includes a constrained update forcing material characteristics of reconstructed atomic number (Z) and density (p) volumes to follow a distribution according to the material database provided. We also propose a probabilistic classification technique in order to manage this material distribution. The overall process produces a chemically segmented volume data and outperforms sequential labelling computed after tomographic reconstruction.

Scaling evalutation of the lattice solid model on the SGI Altix 3700 [evalutation read evaluation]

The lattice solid model is a particle based method which has been successfully employed for simulating the fracturing of rocks, the dynamics of faults, earthquakes and gouge processes. However, results from initial simulations demonstrate that models consisting of only thousands of particles are inadequate to accurately reproduce the micro-physics of seismic phenomenon. Instead, models with millions or tens of millions of particles are required to produce realistic simulations. Parallel computing architectures, such as the SGI Altix 3700, provide the opportunity to solve much larger computational problems than traditional single processor systems. In order to take advantage of high performance systems, a message passing interface version of the lattice solid model has been implemented. Benchmarks, presented in this paper, demonstrate an 80% parallel efficiency for the parallel lattice solid model on 128 processors of the SGI Altix 3700. These results, for a two-dimensional wave propagation problem, indicate the potential for the lattice solid model to simulate more computationally challenging three-dimensional geophysical processes.