Directional Bands Research Articles

Orientation Field Estimation for Noisy Fingerprint Image Enhancement

There is a growing trend towards employing automatic fingerprint identification systems (AFIS) as a viable biometric tool for identity verification. However, this technology is often defeated when attempting to process low-quality fingerprints. A popular technique is to utilize Coherence-Enhancing Diffusion (CED) first to raise fingerprint quality to a level where any recognition takes place. One of the principal functions of CED is to extract orientations by referencing neighbouring gradients. Gradient computations are noise-prone and tend to deviate away from the actual underlying orientation field. This paper proposes a cluster-based computational approach for reliable orientation field estimation based on a directional filter bank framework. The orientations present in fingerprints cluster themselves in a contagious group in the directional bands, that can be exploited towards their reliable estimation. The estimated orientation field then becomes an input data for the CED engine as a pre-computed add-on module to provide much- needed enhancement in noisy fingerprints that subsequently attains in better recognition performance for a given Automated Fingerprint Identification System (AFIS). The experimental procedures reported in this study suggest more accurate orientation results in favour of proposed method than existing techniques even when processing very noisy real-life test data. The improvement in noisy fingerprints is also reported.

Experimental validation of a coprime linear microphone array for high-resolution direction-of-arrival measurements.

Coprime linear microphone arrays allow for narrower beams with fewer sensors. A coprime microphone array consists of two staggered uniform linear subarrays with M and N microphones, where M and N are coprime with each other. By applying spatial filtering to both subarrays and combining their outputs, M+N-1 microphones yield M⋅N directional bands. In this work, the coprime sampling theory is implemented in the form of a linear microphone array of 16 elements with coprime numbers of 9 and 8. This coprime microphone array is experimentally tested to validate the coprime array theory. Both predicted and measured results are discussed. Experimental results confirm that narrow beampatterns as predicted by the coprime sampling theory can be obtained by the coprime microphone array.

Robust multi-scale orientation estimation: Directional filter bank based approach

Orientation estimation is considered as an important task in many subsequent pattern recognition and image enhancement systems. In a noisy environment, the gradient-based estimator provides poor results. A pre-smoothing Gaussian function with an appropriate scale is conventionally used to get improved gradients. Later on, a family of pre-smoothing Gaussian functions with a range of scales is employed for estimation, this is referred to as multi-scale orientation estimator. To provide groundwork for comparison, a more formal framework of multi-scale orientation estimation, based on scale-space axioms, in spatial domain is presented. Then for improvement purposes a Fourier domain approach, where directional filter bank (DFB) structure is embedded in multi-scale orientation estimation framework, is proposed. This is referred to as multi-scale DFB approach. The paper presents the comparison work for estimation of local orientations using multi-scale approaches both in spatial and Fourier domain. In the Fourier-domain approach, two linear combinations are deployed, one across the directional image, and the other across the scales. This is opposed to only one linear combination across the scales, used in simple spatial domain techniques. Further more, the DFB-based Fourier domain approach extracts the best local orientation by comparing and contrasting all possible orientations with their respective strength measures. The strength measure used in Fourier method is based on local variance, free from inaccurate gradient calculation. Simulations are conducted over noisy test images as well as real fingerprints. Our objective results indicate that multi-scale Fourier domain approach always yields better estimates at variable level of noise as compared to stand alone multi-scale spatial domain approaches. The improvements made by Fourier domain estimate can largely be attributed to the use of double linear combination both across the directional bands and across the scales.

Secured Finger Vein Authentication System Using Contourlet Transform and SVM

Biometrics authentication is playing a vital role in providing security and privacy. This paper presents a contemporary approach for identifying an individual using unimodal biometrics. Finger vein based authentication system is a promising technology and now-a-days widely used because of its important features such as resistant to criminal tampering, high accuracy, ease of feature extraction and greater authentication speed. The feature vein patterns extracted by Contourlet transform decompose into directional sub bands in different orientations at various scales. The Support Vector Machine (SVM) classifier is used for pattern matching. Thus the experimental results shows that our proposed method tested on two different databases of finger vein images improves recognition rate with high matching speed.

Microstructure and Mechanical Properties of CP-Ti Processed by 2 ECAP Passes Using a 90° Die at Room Temperature

Equal channel angular pressing (ECAP) deformation for commercial pure titanium (CP-Ti) was successfully conducted using a conventional die with an angle of 90° between the channels at room temperature via route B, in which the billet was rotated 90° along its longitudinal axis between adjacent passes. Each billet was processed for two passes using a ram speed of 26mms-1. The microstructures and mechanical properties of these CP-Ti billets with an initial grain size of ~23μm processed by ECAP were investigated. Experiment results show thin parallel shear bands with a width of 0.3~0.4μm are generated after one ECAP pass, which are composed of large number of dislocation cell blocks. After the two ECAP passes, some various directional bands are generated and the equiaxed and smaller-than-average CBs in local areas begin to appear. In addition, the ultimate strength and microhardness are significantly enhanced to ~725MPa and ~2283MPa, respectively. Meanwhile good elongation of 18.0% to failure is still remained.

Optical characterization of woodpile structures in gelatin emulsions fabricated by optical interference holography

A 4+1-beam optical interference holography technique, with four linearly polarized side beams arranged symmetrically around a circularly polarized central beam, was used to fabricate woodpile structures in holographic gelatin emulsions. The gelatin samples, particularly in three dimensions, were more uniform than those recorded using polymeric photoresists because of the self-supporting property of the gelatin. The gelatin woodpile samples exhibited clear directional stop bands in the angular transmittance measurements. Furthermore, by exploiting the swelling property of the gelatin, we were able to tune these directional stop bands by the amount of swelling. We also modeled the angular dependence of the stop bands by the reflections of the parallel layers inside the woodpile samples and good agreement with the experimental results was obtained.