Cecilia Moloney

A new direction adaptive scheme for image interpolation

We present a novel image interpolation method based on variational models with both smoothing and orientation constraints. By introducing the orientation constraint, we simplify the nonlinear PDE problem into a series of problems with explicit solutions. In our model, the gradient directions for the interpolated pixels are first estimated using a modified orientation diffusion method. Using these estimated gradient directions adaptive directional interpolation is carried out. An effective numerical implementation of the adaptive directional interpolation is presented for the case of upsampling by factors of two. This implementation had very low complexity and is well suited for real-time applications.

An extended visual cryptography scheme without pixel expansion for halftone images

Visual cryptography is a secret sharing scheme which uses images distributed as shares such that, when the shares are superimposed, a hidden secret image is revealed. In extended visual cryptography, the share images are constructed to contain meaningful cover images, thereby providing opportunities for integrating visual cryptography and biometric security techniques. In this paper, we propose a method for processing halftone images that improves the quality of the share images and the recovered secret image in an extended visual cryptography scheme for which the size of the share images and the recovered image is the same as for the original halftone secret image. The resulting scheme maintains the perfect security of the original extended visual cryptography approach.

A ratio edge detector for speckled images based on maximum strength edge pruning

This paper presents an edge detection method which is well-suited to determining accurate and localized edge maps for speckled images. The maximum strength edge pruning ratio of averages (MSP-RoA) method is a ratio-based edge detector which makes effective use of edge orientation information in pruning candidate edge pixels. The method is compared to other speckle-specific edge detection methods. Test results of the MSP-RoA method for simulated speckled images and for airborne synthetic aperture radar (SAR) images are presented.

Development and Testing of Wavelet Modulation for Single-Phase Inverters

This paper introduces a novel modulation technique for single-phase (1 phi) voltage-source (VS) dc-ac power inverters. The proposed modulation technique is based on a newly designed scaling function that is capable of supporting a nonuniform recurrent sampling process. This scaling function generates sets of basis functions that span spaces, of which a collection constructs a nondyadic-type multiresolution analysis. Furthermore, the newly designed scaling function has a dual synthesis scaling function that is designed to reconstruct continuous-time signals from their nonuniform recurrent samples. The proposed wavelet modulation technique is implemented using a MATLAB code that generates switching pulses to activate a SIMULINK model of a 1 phi VS four-pulse (H-bridge) inverter. Several performance tests are conducted for the proposed wavelet-modulated (WM) inverter, when supplying linear, nonlinear, static, and dynamic loads. The results of these tests show significant reduction of the output harmonics along with high magnitude of the output fundamental component. The efficacy of the proposed WM inverter is further demonstrated through a comparison of the random pulsewidth modulation (RPWM) and the pulsewidth modulation (PWM) inverters for supplying the same loads. The comparison results show that the proposed WM inverter is capable of producing outputs with higher quality than the RPWM and PWM inverters.

Analysis and Development of Wavelet Modulation for Three-Phase Voltage-Source Inverters

This paper presents the analysis, development, and implementation of a wavelet modulation (WM) technique for three-phase voltage-source (VS) six-pulse inverters. The WM technique is based on sampling three continuous-time (CT) sinusoidal reference modulating signals in a nonuniform recurrent manner using three sets of scale-based linearly combined wavelet basis functions. These CT signals are recovered from their samples by a three-phase VS six-pulse inverter, which is activated by three sets of synthesis scale-based linearly combined wavelet basis functions. Each set of synthesis basis functions is generated for activating one leg of the three-phase inverter in order to recover one CT reference modulating signal. The WM technique is implemented for both simulation and experimental performance testing. The performances of the WM technique are compared with those obtained using the space vector modulation, random pulsewidth modulation, and hysteresis band current control techniques under the same loading conditions. Simulation and experimental test results show that the proposed WM technique is able to switch a three-phase VS six-pulse inverter to produce outputs with significantly improved fundamental components and low harmonic contents.

A novel visual secret sharing scheme without image size expansion

Over the past few years, increasing concern about the privacy of information shared in computer systems has increased interest in data security. Visual cryptography is a secure secret sharing scheme that divides secret images into shares which on their own reveal no information of the original secret image. Recovery of the secret image can be performed by superimposing the shares. Hence, the process does not require any special software or hardware for cryptographic computations. However, loss of resolution and contrast, and also the image size expansion which results in the need for storage space, are resulting problems and have been the focus of many researchers. In this paper, we propose a novel visual secret sharing scheme without image size expansion. Compared to other schemes of visual cryptography, our perfectly secure scheme not only does not have pixel expansion, but also provides a high quality recovered image.

Development and testing of wavelet packet transform-based detector for ice accretion on wind turbines

This paper introduces a novel method for detecting ice accumulation on wind turbines. The proposed detection method is based on utilizing a multi-resolution analysis to extract specific frequency components present in the direct and quadrature components of the electric current flowing out of a wind generator. The basis of the proposed method lies in the fact that ice accumulation leads to a slow increase in the mass of the wind turbine, which demands higher electromagnetic torque to overcome the iced rotor and blades at each wind speed. The Daubechies db6 basis functions are used to construct the desired multi-resolution analysis for analyzing the current signals. The proposed method has been implemented for simulation tests using MAT-LAB/SIMULINK software. Simulation results show that the proposed method can detect ice accumulation, related vibrations and electromagnetic torque pulsations independent from any pre-defined geometry.

Decorrelating the Structure and Texture Components of a Variational Decomposition Model

The observation has been made by Aujol and Gilboa that the cartoon and texture components of the decomposition of an image should not be correlated, as they are generated from independent processes. They use this observation in order to choose an optimal fidelity parameter lambda for the decomposition process. However, this determination can be quite inefficient since a wide range of parameters lambda must be searched through before an estimated optimal parameter can be found. In the present paper, we take a different approach, in which the cartoon and texture components are explicitly decorrelated by adding a decorrelation term to the energy functional of the decomposition model of Osher, Sole, and Vese (the OSV model). Decomposition results of improved quality over those from the OSV model are obtained, as quantified by a series of new decomposition quality measures, with cartoon and texture information better separated into their respective components. A new derivation of the OSV model is developed which maintains the texture subcomponents g1 and g2 so that discrimination results similar to those from other decomposition models (e.g., from the model of Vese and Osher and Improved Edge Segregation) may be obtained. This derivation is extended to the proposed model, for which discrimination results are obtained in a substantially smaller number of iterations.

Developing a Non-Dyadic MRAS for Switching DC-AC Inverters

This paper introduces a new non-dyadic multiresolution analysis-synthesis (MRAS) structure to generate switching signals for DC-AC inverters. We propose a new method for modifying the Haar scaling function to support a non-uniform recurrent sampling process. This modification is based on a linear combination of scale-based shifted Haar scaling functions. These modified scaling functions are capable of constructing a non-dyadic type MRAS. Synthesis scaling functions associated with the proposed sampling scaling functions are used to activate switching elements of a DC-AC inverter. The output of such an inverter is found to be an accurate approximation of the continuous-time sinusoidal reference signal

Characterization and statistical modeling of phase in single-channel synthetic aperture radar imagery

Traditionally, the phase content in single-channel synthetic aperture radar (SAR) imagery is discarded. This practice is justified by conventional radar resolution theory, which is a theory strictly relevant to point targets. The advent of high-resolution radars permits small targets previously considered to be points to be now treated as extended targets, in which case this theory is not strictly applicable. With this in mind, this paper offers a new insight into the relevance of phase in single-channel SAR imagery. The proposed approach builds on techniques from the fields of complex-valued and directional statistics. In doing so, three main contributions are presented, the first being a novel method for characterizing the phase content. Second, a new statistical model for the phase is considered, and then a set of 15 solely phase-based features are discussed. Our results are demonstrated on real-world SAR datasets for ground-truthed targets. The statistical significance of the information carried in the phase is clearly demonstrated. Furthermore, if applied to a dataset with higher resolution, the proposed techniques are expected to achieve even higher performance.