Nonlinear Edge Research Articles

Extraction and Regularization of Various Building Boundaries with Complex Shapes Utilizing Distribution Characteristics of Airborne LIDAR Points

This study presents an approach for extracting boundaries of various buildings, which have concave boundaries, inner yards, non-right-angled corners, and nonlinear edges. The approach comprises four steps: building point segmentation, boundary tracing, boundary grouping, and regularization. In the second and third steps, conventional algorithms are improved for more accurate boundary extraction, and in the final step, a new algorithm is presented to extract nonlinear edges. The unique characteristics of airborne light detection and ranging (LIDAR) data are considered in some steps. The performance and practicality of the presented algorithm were evaluated for buildings of various shapes, and the average omission and commission error of building polygon areas were 0.038 and 0.033, respectively.

A non-linear complex diffusion-based edge and structure preserving zooming technique for MRI and ultrasound images

In this paper, a non-linear complex diffusion-based edge and structure preserving image zooming technique for Magnetic Resonance Imaging (MRI) and ultrasound images is proposed. The proposed method performs regularisation, edge and structure preservation of digital medical MRI and ultrasound images, which were initially zoomed using one of the linear interpolation methods such as nearest-neighbour, bilinear and bi-cubic. For digital implementations, the proposed model is discretised using finite differences schemes. The scheme is implemented in MATLAB 7.0 and tested for various MRI and ultrasound images. A comparative analysis of the proposed scheme with the standard existing schemes have been performed in terms of Mean Square Error (MSE), Peak Signal-to-Noise Ratio (PSNR), Correlation Parameter (CP), Mean Structure Similarity Index Map (MSSIM) and histogram analysis. The obtained results justify the applicability of the proposed scheme.

HDR Image Compression by Local Adaptation for Scene and Display Using Retinal Model

Adaptation process of retina helps human visual system to see a high dynamic range scene in real world. This paper presents a simple static local adaptation method for high dynamic range image compression based on a retinal model. The proposed simple model aims at recreating the same sensations between the real scene and the range compressed image on display device when viewed after reaching steady state local adaptation respectively. Our new model takes the display adaptation into account in relation to the scene adaptation based on the retinal model. In computing local adaptation, the use of nonlinear edge preserving bilateral filter presents a better tonal rendition in preserving the local contrast and details while avoiding banding artifacts normally seen in local methods. Finally, we demonstrate the effectiveness of the proposed model by estimating the color difference between the recreated image and the target visual image obtained by trial and error method.

Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning

The goal of this study was to determine the acquisition parameters for a low-dose multi-slice CT protocol and to compare the effective dose and the image quality of this low-dose protocol with the image quality of a clinical multi-slice CT protocol, routinely used for visualisation of the head. The low-dose protocol was derived from a clinical multi-slice CT protocol by lowering mA s and kV and increasing the pitch. The low-dose protocol yielded a dose reduction from 1.5 to 0.18 mSv for a multi-slice CT scan of the whole head, whereas noise in the low-dose CT images was increased. For bone segmentation, noise could be reduced by use of a non-linear edge preserving smoothing filter. Tests on ESP and skull phantom indicated that the accuracy of the measurements on low-dose CT is acceptable for image-based planning of maxillofacial and oral implant surgery, reducing the dose by a factor of 8.

Electrothermal simulation of a defect in a solar cell

A local electrothermal simulation of a model solar cell is presented. A rigorous discussion of the heat dissipation mechanisms in a solar cell is performed, showing that the total dissipated heat splits into heating terms (thermalization, recombination, and Joule heat) and different Peltier cooling terms. Such simulations are important for interpreting lock-in thermography images of real solar cells. The simulated model cell consists of a circular noncontacted region surrounded by a grid line and a nonlinear edge shunt. Based on this simulation, a special lock-in thermography operation mode is proposed, which enables noncontacted regions in real solar cells to be imaged. Experimental results confirm the theoretical predictions.

Improvement of Image Quality in Chest MDCT Using Nonlinear Wavelet Shrinkage with Trimmed-thresholding

Multidetector-row computed tomography (MDCT) has dramatically increased the speed of scanning, and allows high-resolution imaging compared with conventional single detector-row CT (SDCT). However, the use MDCT makes use of an increase in volume scanning, and causes a simultaneous increase in radiation dose to the patient. Thus, the radiation dose from the X-ray CT has become a problem in recent years. In this study, nonlinear wavelet-based edge preservation de-noising using trimmed-thresholding was applied to reconstructed low-dose chest MDCT images, and optimal wavelet processing including wavelet functions and thresholding methods was examined. Moreover, the usefulness of the de-noising for reducing radiation dose was examined. As a result of optimized edge preservation de-noising, noise reduction was achieved with little deterioration in image quality, and the wavelet function used at that time was Coiflet's with shorter support. As a result, almost the same quality of reconstructed image of the chest phantom was obtained for conventional scanning and low-dose scanning with the wavelet de-noising method using trimmed- thresholding. That is, the radiation dose from MDCT could be reduced using this wavelet-based de-noising method.

Soliton-like electromagnetic modes: modulation of nonlinear band edge and field distribution

We construct a modulated one-dimensional photonic band gap structures (MPBGS) and investigate the soliton-like modes induced by the nonlinear effect. It is found that due to the nonlinear modulation, the common linear gap of the MPBGS can become narrow or completely disappear, the electromagnetic eigenmodes can enter the common linear gap and develop into soliton-like modes. The field distributions for linear and soliton-like modes are also computed and discussed.

Soliton-like electromagnetic modes: modulation of nonlinear band edge and field distribution

We construct a modulated one-dimensional photonic band gap structures (MPBGS) and investigate the soliton-like modes induced by the nonlinear effect. It is found that due to the nonlinear modulation, the common linear gap of the MPBGS can become narrow or completely disappear, the electromagnetic eigenmodes can enter the common linear gap and develop into soliton-like modes. The field distributions for linear and soliton-like modes are also computed and discussed.

Simple nonlinear dual-window operator for edge detection

We propose a nonlinear edge detection technique based on a two-concentric-circular-window operator. We perform a preliminary selection of edge candidates using a standard gradient and use the dual-window operator to reveal edges as zero-crossing points of a simple difference function depending only on the minimum and maximum values in the two windows. Comparisons with other well-established techniques are reported in terms of visual appearance and computational efficiency. They show that detected edges are surely comparable with Canny's and Laplacian of Gaussian algorithms, with a noteworthy reduction in terms of computational load.

Gaussian-based edge-detection methods-a survey

The Gaussian filter has been used extensively in image processing and computer vision for many years. We discuss the various features of this operator that make it the filter of choice in the area of edge detection. Despite these desirable features of the Gaussian filter, edge detection algorithms which use it suffer from many problems. We review several linear and nonlinear Gaussian-based edge detection methods.

Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak

Operating with a high frequency and a wave guide antenna, the ion Bernstein wave (IBW) experiment on the Frascati Tokamak Upgrade is not dominated, as expected, by nonlinear plasma edge phenomena. By coupling IBW power, a simultaneous increase of plasma density and central electron temperature (⩾2 keV) is produced when the confinement magnetic field is adjusted to set an ion cyclotron resonant layer in the plasma bulk. Transport analysis indicates a reduction of the electron thermal transport inside the internal resonant layer larger than a factor of 2.

All-optical image processing by means of a photosensitive nonlinear liquid-crystal film: edge enhancement and image addition–subtraction

We demonstrate two simple yet efficient all-optical image-processing techniques that use nonlinear photosensitive dye-doped nematic liquid-crystal films, namely, edge enhancement and image addition-subtraction operations. These films require no external bias and function at much lower optical powers and shorter response times than other conventional methods.

Strong correlations in a model of a gauged (2+1)-dimensional nonlinear Schrödinger equation

Phenomena caused by strong correlations between nonlinear modes in planar systems are briefly reviewed. The analysis is restricted to the model of a nonlinear Schrodinger equation. Stationary field distributions are found. The number of particles is obtained as a function of a parameter characterizing the degree of linking of the world lines of excitations. It is shown that, for small values of this parameter, a two-dimensional lattice is characterized by universal attraction, which can be a dynamical cause for the transition to the coherent state. The relation between the chiral nonlinear edge modes and breaking of the Galilei invariance in the system under consideration is discussed.

Quantitative image quality analysis of a nonlinear spatio-temporal filter

Digital temporal and spatial filtering of fluoroscopic image sequences can be used to improve the quality of images acquired at low X-ray exposure. In this study, we characterized a nonlinear edge preserving, spatio-temporal noise reduction filter, the bidirectional multistage (BMS) median filter of Arce (1991). To assess image quality, signal detection and discrimination experiments were performed on stationary targets using a four-alternative forced-choice paradigm. A measure of detectability, d', was obtained for filtered and unfiltered noisy image sequences at different signal amplitudes. Filtering gave statistically significant, average d' improvements of 20% (detection) and 31% (discrimination). A nonprewhitening detection model modified to include the human spatio-temporal visual system contrast-sensitivity underestimated enhancement, predicting an improvement of 6%. Pixel noise standard deviation, a commonly applied image quality measure, greatly overestimated effectiveness giving 67% improvement in d'. We conclude that human testing is required to evaluate the filter effectiveness and that human perception models must be improved to account for the spatio-temporal filtering of image sequences.

Wavelet-based image enhancement in x-ray imaging and tomography

We consider an application of the wavelet transform to image processing in x-ray imaging and three-dimensional (3-D) tomography aimed at industrial inspection. Our experimental setup works in two operational modes-digital radiography and 3-D cone-beam tomographic data acquisition. Although the x-ray images measured have a large dynamic range and good spatial resolution, their noise properties and contrast are often not optimal. To enhance the images, we suggest applying digital image processing by using wavelet-based algorithms and consider the wavelet-based multiscale edge representation in the framework of the Mallat and Zhong approach [IEEE Trans. Pattern Anal. Mach. Intell. 14, 710 (1992)]. A contrast-enhancement method by use of equalization of the multiscale edges is suggested. Several denoising algorithms based on modifying the modulus and the phase of the multiscale gradients and several contrast-enhancement techniques applying linear and nonlinear multiscale edge stretching are described and compared by use of experimental data. We propose the use of a filter bank of wavelet-based reconstruction filters for the filtered-backprojection reconstruction algorithm. Experimental results show a considerable increase in the performance of the whole x-ray imaging system for both radiographic and tomographic modes in the case of the application of the wavelet-based image-processing algorithms.

Coercivity and frequency dependence of track widths and erase bands in thin film media

To understand the data track width, erase bands and the total write width as a function of coercivity and frequency in thin film media, a systematic study was conducted based on triple track profile (TPF) technique using pseudo random sequences (PRS TPF). Frequency harmonics of PRS up to 200 kfci were analyzed to reveal the frequency dependence of the track edge effects. Thin film disks used in this study have coercivities from 1766 Oe to 2878 Oe. Single frequency recording (SF TPF) and MFM (magnetic force microscopy) were utilized for comparison. Regardless of the nonlinear track edge effects, PRS TPF and SF TPF show good correlation over a wide coercivity and frequency range.

Flow past a two– or three–dimensional steep–edged roughness

Flow past a single small planar or three–dimensional roughness mounted on a smooth surface is investigated theoretically for various edge steepnesses, the oncoming planar motion being within a boundary layer or other near–wall shear. Nonlinear edge properties at large Reynolds numbers largely control the flow responses at the three–dimensional roughness wing–tips and the impacts of separation(s), among other features. From analysis and computation, criteria are found for the generation of nonlinear upstream influence, downstream influence and separations, for two– and three–dimensional roughnesses, as well as wing–tip separations. In particular, it is predicted that with a severe edge (e.g. a 90° forward–facing step) the ratio of the upstream separation distance over the roughness edge height is a constant times Re W 1/4 in two dimensions, the constant being approximately 0.142 and the Reynolds number Re W being based on the roughness edge height and the incident velocity slope at the surface. In three dimensions Re W is multiplied by sin ψ as expected physically, where ψ is the tangent angle of the roughness planform. The ratio prediction above is very general, applying not only for any incident shear flow, but also for any front–edge geometry. Other separation and reattachment properties, extensions and a comparison with an experiment, are also discussed.

Localized states in a nonlinear optical system with a binary-phase slice and a feedback mirror

We consider spatiotemporal dynamics in an optical system containing a thin film of nonlinear medium having binary-type refractive nonlinear response and a feedback mirror. Steady-state output transverse patterns consist of a set of localized states, and strongly depend on the initial spatial phase modulation (seeded phase image). These steady-state solution properties can be used for nonlinear image processing and edge detection. System dynamics are studied both theoretically and through numerical simulation.

Voronoi diagrams of polygons: A framework for shape representation

This paper describes an efficient shape representation framework for planar shapes using Voronoi skeletons. This paper makes the following significant contributions. First a new algorithm for the construction of the Voronoi diagram of a polygon with holes is described. The main features of this algorithm are its robustness in handling the standard degenerate cases (colinearity of more than two points; co-circularity of more than three points), and its ease of implementation. It also features a robust numerical scheme to compute non-linear parabolic edges that avoids having to solve equations of degree greater than two. The algorithm has been fully implemented and tested in a variety of test inputs. Second, the Voronoi diagram of a polygon is used to derive accurate and robust skeletons for planar shapes. The shape representation scheme using Voronoi skeletons possesses the important properties of connectivity as well as Euclidean metrics. Redundant skeletal edges are deleted in a pruning step which guarantees that connectivity of the skeleton will be preserved. The resultant representation is stable with respect to being invariant to perturbations along the boundary of the shape. A number of examples of shapes with and without holes are presented to demonstrate the features of this approach.

Detecting danger labels with RAM-based neural networks

An image processing system for the automatic location of danger labels on the back of containers is presented. The system uses RAM-based neural networks to locate and classify labels after a pre-processing step involving specially designed non-linear edge filters and RGB-to-HSV conversion. Results on images recorded at the container terminal in Esbjerg, Denmark, are presented.