Showing papers on "Centroid published in 2002"

Optimal edge-based shape detection

Abstract: We propose an approach to accurately detecting two-dimensional (2-D) shapes. The cross section of the shape boundary is modeled as a step function. We first derive a one-dimensional (1-D) optimal step edge operator, which minimizes both the noise power and the mean squared error between the input and the filter output. This operator is found to be the derivative of the double exponential (DODE) function, originally derived by Ben-Arie and Rao (1994). We define an operator for shape detection by extending the DODE filter along the shape's boundary contour. The responses are accumulated at the centroid of the operator to estimate the likelihood of the presence of the given shape. This method of detecting a shape is in fact a natural extension of the task of edge detection at the pixel level to the problem of global contour detection. This simple filtering scheme also provides a tool for a systematic analysis of edge-based shape detection. We investigate how the error is propagated by the shape geometry. We have found that, under general assumptions, the operator is locally linear at the peak of the response. We compute the expected shape of the response and derive some of its statistical properties. This enables us to predict both its localization and detection performance and adjust its parameters according to imaging conditions and given performance specifications. Applications to the problem of vehicle detection in aerial images, human facial feature detection, and contour tracking in video are presented.

The centroid of the symmetrical Kullback-Leibler distance

Abstract: This paper discusses the computation of the centroid induced by the symmetrical Kullback-Leibler distance. It is shown that it is the unique zeroing argument of a function which only depends on the arithmetic and the normalized geometric mean of the cluster. An efficient algorithm for its computation is presented. Speech spectra are used as an example.

On the reverse Lp–busemann–petty centroid inequality

Abstract: The volume of the L p -centroid body of a convex body K ⊂ R d is a convex function of a time-like parameter when each chord of K parallel to a fixed direction moves with constant speed. This fact is used to study extrema of some affine invariant functionals involving the volume of the L p -centroid body and related to classical open problems like the slicing problem. Some variants of the L p -Busemann-Petty centroid inequality are established. The reverse form of these inequalities is proved in the two-dimensional case.

Biometric identification system by lip shape

Abstract: Biometrics systems based on lip shape recognition are of great interest, but have received little attention in the scientific literature. This is perhaps due to the belief that they have little discriminative power. However, a careful study shows that the difference between lip outlines is greater than that between shapes at different lip images of the same person. So, biometric identification by lip outline is possible. In this paper the lip outline is obtained from a color face picture: the color image is transformed to the gray scale using the transformation of Chang et al. (1994) and binarized with the Ridler and Calvar threshold. Considering the lip centroid as the origin of coordinates, each pixel lip envelope is parameterized with polar (ordered from -/spl pi/ to +/spl pi/) and Cartesian coordinates (ordered as heights and widths). To asses identity, a multilabeled multiparameter hidden Markov model is used with the polar coordinates and a multilayer neural network is applied to Cartesian coordinates. With a database of 50 people an average classification hit ratio of 96.9% and equal error ratio (EER) of 0.015 are obtained.

Minimum variance centroid thresholding.

Abstract: Image-processing thresholding algorithms are extended segmentation tools that are suitable for tracking applications. The centroid of the tracked image distribution is a good point of reference for the location of the image. We describe a new thresholding technique that is based on the estimation of the optimum threshold for achieving minimal variance in the centroid of the processed image. Experimental proofs for evaluating the technique's performance are given. The direct extension of these results to Shack-Hartmann wave-front sensors is also shown.

On the Optimum Synthesis of Four-bar Linkages Using Differential Evolution and the Geometric Centroid of Precision Positions

Abstract: Mechanism synthesis, the identification of the parameters of a mechanism, has been extensively studied especially for four-bar linkages using graphical and numerical optimization approaches. Graphical techniques follow a number of predefined steps and rely heavily on the user. Numerical optimization techniques that require the user to provide "good initial guesses" or bounds for the design variables have also been applied. In general, a linkage is synthesized for function generation, motion generation, and path generation. This article studies four-bar mechanism synthesis by combining Differential Evolution, an evolutionary optimization scheme that can search outside the initial defined bounds for the design variables, and a newly developed novel technique called the Geometric Centroid of Precision Points (GCPP) and the distant precision point in defining the initial bounds for the design variables. The developed methodology has been applied to the synthesis of four-bar linkages for path generation with p...

A comparative study of centroid-based, neighborhood-based and statistical approaches for effective document categorization

Abstract: Associating documents to relevant categories is critical for effective document retrieval. Here, we compare the well-known k-nearest neighborhood (kNN) algorithm, the centroid-based classifier and the highest average similarity over retrieved documents (HASRD) algorithm, for effective document categorization. We use various measures such as the micro and macro F1 values to evaluate their performance on the Reuters-21578 corpus. The empirical results show that kNN performs the best, followed by our adapted HASRD and the centroid-based classifier for common document categories, while the centroid-based classifier and kNN outperform our adapted HASRD for rare document categories. Additionally, our study clearly indicates that each classifier performs optimally only when a suitable term weighting scheme is used All these significant results lead to many exciting directions for future exploration.

An improved thermodynamic energy estimator for path integral simulations

Abstract: A new path integral energy estimator is presented that improves upon the thermodynamic energy estimator via a free particle projection. This centroid thermodynamic estimator significantly reduces the numerical noise of the thermodynamic estimator. The debate as to which estimator is better (virial, centroid virial, or thermodynamic) is partially resolved. The centroid estimators are found to be significantly better than their noncentroid analogues. The new centroid thermodynamic estimator has accuracy close to the centroid virial estimator, and may have particular advantages when derivatives of the potential are expensive to evaluate.

A dual pixel-type array for imaging and motion centroid localization

Abstract: An imager chip has been designed, fabricated, and tested having two unique pixel types interleaved on the same array. The dual-pixel design enables optimization for two separate tasks. One type of pixel is an active pixel sensor (APS), which is used to produce a low-noise image. The other type is a custom-designed pixel optimized for computing the centroid of a moving object in the scene. The APS array is 120 columns /spl times/36 rows, with a pixel size of 14.7/spl times/14.7 /spl mu/m. The centroid array has 60 columns and 36 rows, with a larger pixel size of 29.4/spl times/29.4 /spl mu/m. The chip was fabricated using standard scalable rules on a 0.5 /spl mu/m 1P3M CMOS process. APS images were taken at a frame rate of 30 fps-8300 fps and centroid data was taken at a rate of 180-3580 (x,y) coordinates per second. The chip consumed 2.6 mW.

Centroid-based methods for calculating quantum reaction rate constants: Centroid sampling versus centroid dynamics

Abstract: A new method was recently introduced for calculating quantum mechanical rate constants from centroid molecular dynamics (CMD) simulations [E. Geva, Q. Shi, and G. A. Voth, J. Chem. Phys. 115, 9209 (2001)]. This new method is based on a formulation of the reaction rate constant in terms of the position-flux correlation function, which can be approximated in a well defined way via CMD. In the present paper, we consider two different approximated versions of this new method, which enhance its computational feasibility. The first approximation is based on propagating initial states which are sampled from the initial centroid distribution, on the classical potential surface. The second approximation is equivalent to a classical-like calculation of the reaction rate constant on the centroid potential, and has two distinct advantages: (1) it bypasses the problem of inefficient sampling which limits the applicability of the full CMD method at very low temperatures; (2) it has a well defined TST limit which is directly related to path-integral quantum transition state theory (PI-QTST). The approximations are tested on a model consisting of a symmetric double-well bilinearly coupled to a harmonic bath. Both approximations are quite successful in reproducing the results obtained via full CMD, and the second approximation is shown to provide a good estimate to the exact high-friction rate constants at very low temperatures.

Quantitative assessment of flow velocity-estimation algorithms for optical Doppler tomography imaging

Abstract: We present a quantitative comparison of three categories of velocity estimation algorithms, including centroid techniques (the adaptive centroid technique and the weighted centroid technique), the sliding-window filtering technique, and correlation techniques (autocorrelation and cross correlation). We introduce, among these five algorithms, two new algorithms: weighted centroid and sliding-window filtering. Simulations and in vivo blood flow data are used to assess the velocity estimation accuracies of these algorithms. These comparisons demonstrate that the sliding-window filtering technique is superior to the other techniques in terms of velocity estimation accuracy and robustness to noise.

User Manual and Supporting Information for Library of Codes for Centroidal Voronoi Point Placement and Associated Zeroth, First, and Second Moment Determination

Abstract: The theory, numerical algorithm, and user documentation are provided for a new ''Centroidal Voronoi Tessellation (CVT)'' method of filling a region of space (2D or 3D) with particles at any desired particle density. ''Clumping'' is entirely avoided and the boundary is optimally resolved. This particle placement capability is needed for any so-called ''mesh-free'' method in which physical fields are discretized via arbitrary-connectivity discrete points. CVT exploits efficient statistical methods to avoid expensive generation of Voronoi diagrams. Nevertheless, if a CVT particle's Voronoi cell were to be explicitly computed, then it would have a centroid that coincides with the particle itself and a minimized rotational moment. The CVT code provides each particle's volume and centroid, and also the rotational moment matrix needed to approximate a particle by an ellipsoid (instead of a simple sphere). DIATOM region specification is supported.

Harmonic cut and regularized centroid transform for localization of subcellular structures

Abstract: Two novel computational techniques, harmonic cut and regularized centroid transform, are developed for segmentation of cells and their corresponding substructures observed with an epi-fluorescence microscope. Harmonic cut detects small regions that correspond to subcellular structures. These regions also affect the accuracy of the overall segmentation. They are detected, removed, and interpolated to ensure continuity within each region. We show that interpolation within each region (subcellular compartment) is equivalent to solving the Laplace equation on a multi-connected domain with irregular boundaries. The second technique, referred to as the regularized centroid transform, aims to separate touching compartments. This is achieved by adopting a quadratic model for the shape of the object and relaxing it for final segmentation.

The Design and Characterisation of an Optical VLSI Processor for Real Time Centroid Detection

Abstract: The integration of photo-detectors onto a standard CMOS integrated circuit is presented. This device provides the optical front end for a real time centroid detection system to be used as part of a larger system for implementing a Shack-Hartmann wavefront sensor. A hardware emulation system containing a Field Programmable Gate Array is used to prototype suitable algorithms prior to IC fabrication. Data is presented on the performance of photodetectors and the ability to extract in real time a centroid coordinate.

The Centroid? Where would you like it to be be?

Abstract: The concept of a centroid is useful for many spatial applications, and the determination of the centroid of a plane polygon is standard functionality in most Geographic Information System (GIS) software. A common reason for determining a centroid is to create a convenient point of reference for a polygon, often for positioning a textual label. For such applications, the rigour with which the centroid is determined is not critical, because in the positioning of a label, for example, the main criteria is that it be within the polygon and reasonably central for easy interpretation. However, there may be applications where the determination of a centroid has, at the very least, an impact on civic pride and quite possibly financial repercussions. We refer here to an administrative or natural region where a nominated centroid has a certain curiosity value with the potential to become a tourist attraction. Such centroids provide economic benefit to those in a sub-region, usually in close proximity to the centroi...

Bilinear interpolation centroid algorithm used for circular optical target location

Abstract: In the close digital photogrammetric three-dimension coordinates measurement, the circular target is often taken as imaging feature and mounted on the measured object or the probe for 3D coordinates detection. The accuracy with which circular targets are located determines the effectiveness of measurement. Subpixel level accuracy is one of the methods that can improve the accuracy of target location. Many methods which based on subpixel edge or centroid detection have been developed and analyzed for target location, but little research focused on circular optical target location. In this research, a new algorithm named bilinear interpolation centroid algorithm was developed for circular optical target subpixel location. In this technique, the accuracy of the squared gray weighted centroid algorithm can be improved by increasing the available pixels which obtained by bilinear interpolation. The intensity profile of the imaging points and the signal to noise ratio, which affect the subpixel location accuracy, are optimized by automatic exposure control. The experiments have shown that the accuracy of this algorithm is better than the traditional centroid algorithm, and the absolute error of less than 0.0 1 pixels is obtained on the image of a rigid reference bar.

An effective centroid Hamiltonian and its associated centroid dynamics for indistinguishable particles in a harmonic trap

Abstract: We show that incorporating the effects of Bose–Einstein or Fermi–Dirac quantum statistics within the centroid molecular dynamics formalism leads to additional correlations in the system due to exchange effects. In the case of Bose–Einstein statistics they appear as an additional attraction between physical particles while an additional repulsion is observed for Fermi–Dirac statistics. We show that we can account for these correlations through the effective centroid Hamiltonian. Within the approach based on the phase space centroid density, this Hamiltonian depends on centroid momenta in a nonclassical way. We illustrate the above findings using a simple model of two bosons and fermions in a harmonic potential. The average of a centroid variable along centroid trajectories based on such an effective Hamiltonian can be used to study the equilibrium properties of quantum systems. Is is also shown that the dynamics of the centroid variables derived from the quantum mechanical dynamics of the corresponding physical observables does not depend on exchange effects for a harmonic system.

High speed digital CMOS 2D optical position sensitive detector

Abstract: In this paper we present a 2-D optical sensor array for position sensing applications. The 20 by 20 pixels sensor implements an analog intensive parallel computation for the estimation of the centroid of a light distribution impinging on the photosensitive area. The photogenerated signal is first analog preprocessed by means of a distributed image peak detector; contour digitization follows for extracting the image centroid position. The sensor, fabricated in standard 0.8µm CMOS technology performs up to 230k frames/s and exhibits a power consumption which is proportional to the square root of the number of pixels.

Face direction detector

Abstract: PROBLEM TO BE SOLVED: To provide a face direction detector which detects the direction of the face based on a picked-up image of an imaging means. SOLUTION: In a looking-aside monitor and alarm device applying the face direction detector, a centroid position G of an eye EO, a height H of the eye EO, and a width W of the eye EO of a full-faced face in an image picked up by the imaging means are defined as a reference centroid position G, a reference height H, and a reference width W respectively. and a vertical direction decision means compares a centroid position Gi and a height Hi of the eye in an image of the eye detected by an eye information detection means, with the reference centroid position G and the reference height H respectively to determine the vertical direction of the face, and a lateral direction decision means compares the centroid position Gi and a width Wi of the eye in the image of the eye detected by the eye information detection means, with the reference centroid position G and the reference width W respectively to determine the lateral direction of the face. COPYRIGHT: (C)2004,JPO

Centroid dynamics with quantum statistics

Abstract: This paper discusses the recent developments of a new molecular dynamics approach for the study of quantum dynamics for systems obeying Bose-Einstein statistics. The formalism is based on the mapping of a quantum mechanical system onto a set of phase space variables. These phase space variables are associated with the centroid (center-of-mass) of a Feynman path. We present the essential features of the formalism for the representation of operators and correlation functions and discuss some aspects of its practical implementation. We also present a recently developed simplified model for superfluid environments, based on an effective centroid potential approximation to the partition function. In the context of this model, we introduce a new expression for the calculation of the condensate fraction based on the off-diagonal one-particle density matrix. We perform calculations for a many-particle system where the masses and pair interactions correspond to those of helium. The results show that this simplified model exhibits Bose-Einstein condensation below a certain characteristic temperature.

Pointing accuracy improvement using model-based noise reduction method

Abstract: A new method for improving centroid accuracy, thereby pointing accuracy, is proposed. Accurate centroid estimation is critical for free-space optical communications where the number of photons from the reference optical sources such as stars or an uplink beacon is limited. It is known that the centroid accuracy is proportional to the SNR. Presence of various noise sources during the exposure of CCD can lead to significant degradation of the centroid estimation. The noise sources include CCD read noise, background light, stray light, and CCD processing electronics. One of the most widely used methods to reduce the effects of the noise and background bias is the thresholding method, which subtracts a fixed threshold from the centroid window before centroid computation. The approach presented here, instead, utilizes the spot model to derive the signal boundary that is used to truncate the noise outside the signal boundary. This process effectively reduces both the bias and the noise. The effectiveness of the proposed method is demonstrated through simulations.

Paper-folding and Euler’s Theorem Revisited

Abstract: Given three points O, G, I , we give a simple construction by paperfolding for a triangle having these points as circumcenter, centroid, and incenter. If two further points H and N are defined by OH = 3OG = 2ON, we prove that this procedure is successful if and only if I lies inside the circle on GH as diameter and differs from N . This locus for I is also independently derived from a famous paper of Euler, by complementing his calculations and properly discussing the reality of the roots of an algebraic equation of degree 3.

An Incremental Multi-Centroid, Multi-Run Sampling Scheme for k-medoids-based Algorithms - Extended Report

Abstract: Data clustering has become an important task for discovering significant patterns and characteristics in large spatial databases. The Mufti- Centroid, Multi-Run Sampling Scheme (MCMRS) has been shown to be effective in improving the k-medoids-based clustering algorit hms in our previous work. In this paper, a more advanced sampling scheme termed Incremental MultiCentrozd, Multi-Run Sampling Scheme (IMCMRS) is proposed for k-medoidsbased clustering algorithms. Experimental results demonstrate the proposed scheme can not only reduce by more than 80’ZOcomputation time but also reduce the average distance per object compared with CLARA and CLARANS. IMCMRS is also superior to MCMRS.

Method and system for determining and correcting image orientation angle

Abstract: A simple and robust method for determining the orientation angle of a scanned image or the angular orientation of an object in an electronic image based on using descriptors of the image and systems that implement the method are disclosed. A system including means for acquiring the electronic image, means for determining image centroid coordinates, means for obtaining second order moments corresponding to the image, and, means for determining an orientation angle of a principal axis of the image implements the method.

Methods and systems for making disposable absorbent article having graphics

Abstract: An absorbent article including one or more graphics disposed thereon and a method and system for making the same are provided according to the present invention. A picture is taken of the graphic. Based on the picture, a centroid position of the graphic is determined. The centroid position is compared with a target position. Based on the variation of the centroid position with the target position, the processing is adjusted so as to apply the graphic as desired.

Optimized methods for focal spot location using center-of-mass algorithms

Abstract: In general the center of mass technique is a fast and robust way to approximate the location of a focal spot. This paper discusses in detail the relationship between the focal spot location and the center of mass. We start with a mathematical analysis and conclude with a few practical ideas to improve the accuracy of the center of mass technique.

The centroid shift of the 5d levels of Ce3+ with respect to the 4f levels in ionic crystals, a theoretical investigation

Abstract: The centroid shifts of the 5d level of Ce 3+ in BaF 2 , LaAlO 3 and LaCl 3 have been calculated using the ionic cluster approach. By applying configuration interaction as extension of the basic HF-LCAO approach the dynamical polarization contribution to the centroid shift was calculated. This was found to be only successful if basis sets are used optimized for polarization of the anions.

Kernel Enabled K-Means Algorithm

Abstract: We present a novel method to learn arbitrary cluster boundaries by extending the k-means algorithm to use Mercer kernels. We inter- pret each cluster centroid as a linear com- bination of the cluster points in the higher dimensional space and use this formulation to kernel enable the k-means algorithm. The advantage of this formulation is that we work in the higher dimensional kernel space where it is easier to nd smooth surfaces which separate points belonging to di clus- ters. We also extend our formulation to the non separable case by penalizing the violat- ing points quadratically. We show that the clusters obtained vary as a function of the width parameter of the Gaussian kernel.