Showing papers on "Centroid published in 1997"

Surface-marker cluster design criteria for 3-D bone movement reconstruction

Abstract: When three-dimensional (3-D) human or animal movement is recorded using a photogrammetric system, bone-embedded frame positions and orientations are estimated from reconstructed surface marker trajectories using either nonoptimal or optimal algorithms. The effectiveness of these mathematical procedures in accommodating for both photogrammetric errors and skin movement artifacts depends on the number of markers associated with a given bone as well as on the size and shape characteristics of the relevant cluster. One objective of this paper deals with the identification of marker cluster design criteria aimed at the minimization of error propagation from marker coordinates to bone-embedded frame position and orientation. Findings allow for the quantitative estimation of these errors for any given cluster configuration and suggest the following main design criteria. A cluster made up of four markers represents a good practical compromise. Planar clusters are acceptable, provided in quasi-isotropic distribution. The root mean square distance of the markers from their centroid should be greater than ten times the standard deviation of the marker position error. The second objective of this paper deals with the identification of the optimal cluster position and orientation on the limb aimed at the minimization of error propagation to anatomical landmark laboratory coordinates. Cluster position should be selected to minimize skin movement artifacts. The longest principal axis of the marker distribution should be oriented toward the relevant anatomical landmark position.

Effects of the inversion layer centroid on MOSFET behavior

Abstract: The effects of the average inversion-layer penetration, the inversion-layer centroid, on the inversion-charge density and the gate-to-channel capacitance have been analyzed. The quantum model has been used, and a variety of data have been obtained by self-consistently solving the Poisson and Schrodinger equations. An empirical expression for the centroid position that is valid for a wide range of electrical and technological variables has been obtained and has been applied to accurately model the inversion-layer density and capacitance.

Subpixel position measurement using 1D, 2D and 3D centroid algorithms with emphasis on applications in confocal microscopy

Abstract: The accuracy with which centroid algorithms in 1D, 2D and 3D can estimate an object's position has been investigated. Three factors that can influence the method's accuracy have been investigated: systematic error of the algorithm, influence of photon noise and the influence of perturbations such as scanning nonlinearity. The variation of the accuracy with parameters that are relevant for confocal microscopy, such as object diameter and photon noise/pixel, has been considered. Theory and simulations presented show that the variation of the accuracy with respect to such parameters can differ drastically between the 1D, 2D and 3D cases. Experiments performed using microspheres show that the magnitudes of the three types of error can be approximately the same under normal operating conditions and that it is therefore necessary to take all three into account when assessing the total error.

Maximum a posteriori estimation of wave-front slopes using a Shack–Hartmann wave-front sensor

Abstract: Current methods for estimating the wave-front slope at the pupil of a telescope by using a Shack–Hartmann wave-front sensor (SH–WFS) are based on a simple centroid calculation of the irradiance distributions (spots) recorded in each subaperture. The centroid calculation does not utilize knowledge concerning the correlation properties of the slopes over the subapertures or the amount of light collected by the SH–WFS. We present the derivation of a maximum a posteriori (MAP) estimation of the irradiance centroids by incorporating statistical knowledge of the wave-front tilts. Information concerning the light level in each subaperture and the relative spot size is also employed by the estimator. The MAP centroid estimator is found to be unbiased, and the mean square error performance is upper bounded by that exhibited by the classical centroid technique. This error performance is demonstrated by using Kolmogorov wave-front slope statistics for various light levels.

A vector quantization algorithm based on the nearest neighbor of the furthest color

Abstract: In order to optimize the codebook used by the vector quantization compression scheme, we have developed a process based on the max-min algorithm. This process optimizes color space partitioning from vector blocks selected iteratively within the training set according to three algorithms. The partitioning algorithm is based on the nearest neighbor query. The selection algorithm searches the furthest color of the nearest vector block of the training set already computed. A centroid process generates the codebook in refining the vector block selection. In order to counterbalance cases of study for which the centroid process modifies the vector block selection, we have introduced three tests. These tests restrict the training set from which representative colors can be selected.

A method for calculating the circularity of movement trajectories.

Abstract: A method for computing the circularity of any closed two-dimensional trajectory of arbitrary shape is described. The core of this technique is the derivation of moments of area for each closed contour defined by perimeter coordinates. The method can be used to analyze two-dimensional data of any form, and provides output information including the number of closed contours within the data set, the area of each contour, the position of the centroid of each contour, the orientation of each contour, and the parameters of the ellipse that best fits each contour. A number of applications are discussed, including the comparison of kinematic trajectories, the calculation of cross-sectional areas from digitized MRI scans, and the analysis of phase portraits.

Relevant parameters for tip-tilt systems of large telescopes

Abstract: In order to provide criteria for the design of tip-tilt systems on large telescopes, we derive analytic formulae for the aberrations of the tip-tilt corrected wavefront as a function of the tracking algorithm and of the tracking frequency. We present a new definition for the required bandwidth of tip-tilt systems based upon the residual high order aberrations, and we suggest a new, simple method to eliminate the influence of coma on the image centroid measurement. The effect of the science camera pixel size on the image quality is investigated. A simple approximation is given for the power spectrum of the image motion, and measured power spectra are compared to this approximation. We show that in order to measure the rms image motion properly, it is important to run the measurement over a sufficient period of time (>10 min). In a second paper (Glindemann et al. 1997) in this journal, a tip-tilt system (CHARM) is presented where the parameters derived here are used to evaluate the system performance.

Apparatus and method for image reduction

Abstract: The present invention provides an image reducing system and method capable of retaining fine lines in a reduced image by reducing an original image and by quickly forming the reduced image with high quality. The method includes specifying positions of pixels of a reduced image in the original image according to reduction ratios, extracting a run of pieces of the same color information about the color of the pixels of the original image as a line, determining the line width of the extracted line and determining the line width after reduction in the reduction ratios based on the line width of the extracted line and calculating the centroid of the extracted line, and retaining the color information about the extracted line at a reduced pixel near the centroid on the basis of the centroid of the extracted line and the line width after reduction. The method further performs the step of determining the color information about each reduced pixel based on the retained color information.

Method and apparatus for training Hidden Markov Model

Abstract: HMM training method comprising a first parameter predicting step, a centroid state set calculating step, a reconstructing step, a second parameter predicting step and a control step. In the first parameter predicting step, a parameter of an HMM (hidden Markov model) is predicted based on training data. In the centroid state set calculating step, a centroid state set is calculated by clustering the state of said HMM whose parameter is predicted in the first parameter predicting step. In the reconstructing step, an HMM is reconstructed with using the centroid state calculated in the centroid state set calculating step. In the second parameter predicting step, predicted a parameter of the HMM reconstructed in the reconstructing step with using the training data. And, the centroid step is reexecuted by the control step in the case that a likelihood of the HMM whose parameter is predicted in the second parameter predicting step does not satisfy a predetermined condition.

Determining the probabilities of natural resting aspects of parts from their geometries

Abstract: Proposes a computationally‐simple method, based on the centroid solid angle, for computing the probability distributions of the natural resting aspects of small parts, the fore‐knowledge of which can improve the design of vibratory feeders and orienting devices. The centroid solid angle (CSA) hypothesis postulates that the probability of a part coming to rest on a particular aspect is directly proportional to the solid angle subtended by the aspect with respect to the centroid (the centroid solid angle) and inversely proportional to the height of the centroid from the aspect in question. When benchmarked against Boothroyd’s energy barrier method, its results did not deviate from those of the energy barrier method by more than 0.04. Examines studies of a cylindrical prismatic part and a symmetrical T‐shaped prism. The drop tests used to obtain the authors’ empirical data were validated by experiments conducted on vibratory bowl feeders, subjected to different vibration frequencies. The tracks of one of the...

A Model-Based Approach for the Measurement of Eye Movements Using Image Processing

Abstract: This paper describes a video eye-tracking algorithm which searches for the best fit of the pupil modeled as a circular disk. The algorithm is robust to common image artifacts such as the droopy eyelids and light reflections while maintaining the measurement resolution available by the centroid algorithm. The presented algorithm is used to derive the pupil size and center coordinates, and can be combined with iris-tracking techniques to measure ocular torsion. A comparison search method of pupil candidates using pixel coordinate reference lookup tables optimizes the processing requirements for a least square fit of the circular disk model. This paper includes quantitative analyses and simulation results for the resolution and the robustness of the algorithm. The algorithm presented in this paper provides a platform for a noninvasive, multidimensional eye measurement system which can be used for clinical and research applications requiring the precise recording of eye movements in three-dimensional space.

Triangular element refinement in automatic adaptive mesh generation

Abstract: Given the nature of many magnetic field problems however, where very narrow material regions and curved boundaries exist, the angle condition is often difficult to satisfy using the standard centroid refinement approach. A new refinement strategy is proposed for use in an adaptive procedure. The method developed places new nodes in regions of high solution error such that the benefit of the Delaunay re-triangulation algorithm is fully realised. Results show that the improved mesh geometry obtained with this method compared with the conventional centroid approach produces a more efficient mesh, where less nodes are needed to obtain the same solution accuracy. New algorithms with the purpose of removing thin elements and obtaining a gradual transition in node density in the mesh after each refinement step are also described.

Two-dimensional shape recognition using oriented-polar representation

Abstract: To deal with such a problem as object recognition of position, scale, and rotation invariance (PSRI), we utilize some PSRI properties of images obtained from objects, for example, the centroid of the image. The corresponding position of the centroid to the boundary of the image is invariant is spite of rotation, scale, and translation of the image. To obtain the information of the image, we use the technique similar to Radon transform, called the oriented-polar representation of a 2-D image. In this representation, two specific points, the centroid and the weighted mean point, are selected to form an initial ray, then the image is sampled with N angularly equispaced rays departing from the initial rays. Each ray contains a number of intersections and the distance information obtained from the centroid to the intersections. The shape recognition algorithm is based on the least total error of these two items of information. Together with a simple noise removal and a typical backpropagation neural network, this algorithm is simple, but the PSRI is achieved with a high recognition rate.

Device and method for generating image

Abstract: PROBLEM TO BE SOLVED: To easily prepare a three-dimensional(3D) image by discriminating whether a polygon face to be prepared is located near a contour coordinate related to an object or not when the polygons of 3D models constituting the object of polygons are merged so as to reduce its number SOLUTION: A representative point producing device 28 calculates the coordinates of representative points on the respective polygon faces to be deformed by merging apexes For example, a merged apex coordinate and the centroid coordinates of three apexes of each deformed polygon are calculated A merge discriminating device 30 for the apex reads a voxel value corresponding to each coordinate of the representative point from a contour information memory device 22 and discriminates whether the read voxel value is '1' or '0' When the discriminated result shows '1' concerning all the respective voxel values, all the representative points are matched with any contour point, and a coupling reference is satisfied When the discriminated result shows '0' concerning at least one of respective voxel values, on the other hand, the merging reference is not satisfied

Method and device for encoding object contour by using centroid

Abstract: A centroid-based object contour encoding method and device for encoding still images and moving pictures by rendering a more accurate contour representation with increased compression. The method includes the determination of a centroid and incrementing angle, the determination of distances between the centroid and boundary pixels on an object, and the encoding of the information determined. For moving pictures, the difference between the data of a current frame and the data of a previous frame are encoded by discrete cosine transforming and variable-length coding of the difference data.

Vehicle detecting method

Abstract: PROBLEM TO BE SOLVED: To exactly and easily recognize a vehicle based on a binarized image, to by detecting the centroid position of a candidate vehicle area and excluding this area from the recognizing object of the vehicle when the centroid position is out of a prescribed range. SOLUTION: A camera 1 outputs an image signal corresponding to a picked-up monochromatic image to an image processor 3. In the image processor 3, internal holes or neighbor black areas are collected into one lot and binarized by expanding black sections in the image and afterwards, noise removing processing is executed for removing mixed areas. Then, the centroid position of the black area is found and when the centroid position is out of a prescribed range, that black area is excluded from the recognizing object as the vehicle. When the centroid position is inside the prescribed range, preferably further, parameters such as the aspect ratio of the black area, area ratio between the real area of the black area and the area of a rectangular area in contact with the black area and the height of highest part in the black area are successively found and when any one of these parameters is correspondent to prescribed conditions, that black area is excluded from the recognizing object as the vehicle.

Centroid moment tensor inversion of low-frequency seismic spectra using Green's functions for aspherical earth models

Abstract: SUMMARY We present a new method for centroid moment tensor (CMT) inversion, in which we employ the Green's function computed for aspherical earth models using the Direct Solution Method. We apply this method to CMT inversion of low-frequency seismic spectra for the 1994 Bolivia and 1996 Flores Sea deep earthquakes. The estimated centroid locations agree well with those obtained by multiple-shock analyses using body-wave data. This shows that it is possible to obtain reliable CMT solutions by analyses of low-frequency seismic spectra using accurate Green's functions computed for present 3-D earth models.

Dynamics of quantum particles by path-integral centroid simulations: The symmetric Eckart barrier

Abstract: The path-integral centroid approach has been applied to study the dynamical properties of a flux of protons impinging on a symmetric Eckart barrier. The mean transmission coefficient, transmitted flux, and kinetic energy of transmitted particles have been calculated by path-integral centroid simulations as a function of temperature, and compared to exact results obtained from the solution of the Schrodinger equation. The studied temperatures cover the crossover from a classical regime, where the barrier crossing is thermally activated, to a quantum regime, where the barrier crossing is dominated by tunneling of low energy particles. We show, in agreement with previous studies, that the centroid density is a central quantity to derive dynamical properties. Moreover, we find that the equilibrium internal energy obtained for the centroid fixed at the barrier top, reproduces closely the difference between the mean kinetic energy of transmitted and incident particles, and it can be used to define a velocity (p...

Adaptive suboptimum detection of optical PPM signal with detection matrix and centroid tracking

Abstract: In some applications of optical communication systems, such as satellite optical communication and atmospheric optical communication, the optical beam wanders on the detector surface due to vibration and turbulence effects, respectively. The wandering of the beam degrades the communication system performance. In this research, we derive a mathematical model of an optical communication system with a detection matrix to improve the system performance for direct detection pulse position modulation (PPM) We include a centroid tracker in the communication system model. The centroid tracker tracks the center of the beam. Using the position of beam center and an apriori model of beam spreading we estimate the optical power on each pixel (element) in the detection matrix. Based on knowledge of the amplitudes of signal and noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the detection matrix for communication signals. Tuning the gain is based on the mathematical model derived in this research. This model is defined as suboptimal due to some approximations in the development and is a suboptimum solution to the optimization problem of n multiplied by m free variables, where U,mare the dimensions of the detection matrix. Comparison is made between the adaptive suboptimum model and the standard model. From the mathematical analysis and the results of the comparison it is clear that this model improves significantly communication system performance.

Centroids, Centers, Medians: What is the Difference?

Abstract: Consider a finite subset F of a real normed space. In this paper we try to evaluate the largest possible distance between pairs of points which are, for F, the centroid, a center, or a median. The results seem to show that only when X is a two-dimensional, strictly convex space, or when X is a Hilbert space, what the geometrical intuition indicates is more or less true. We give some examples showing some of the 'pathological' situations which can arise. Also, we indicate some open problems.

Phonetically adaptive cepstrum mean normalization for acoustic mismatch compensation

Abstract: We propose a new technique that compensates for an acoustic mismatch. This technique is simple and can estimate the acoustic mismatch more accurately than conventional cepstrum mean normalization (CMN), because it takes into consideration the kind of phonemes and their frequency, and can calculate the acoustic mismatch in detail. In this procedure the acoustic mismatch can be estimated as the difference between the centroid vector of distorted speech and that of acoustic models. The cepstral mean of distorted speech is the centroid vector including the distortion. The centroid vector calculated from parameters of acoustic models is regarded as the centroid vector when the distorted speech is assumed to be clean speech. The acoustic models used for calculation are for phonemes that appear in the transcription of the speech. This technique achieves a high word error reduction rate of 73% for ordinary analog telephone speech and 70% for wireless telephone handset speech.

Product loading planning device

Abstract: PROBLEM TO BE SOLVED: To draft a loading plan of high transporting efficiency by obtaining an evaluation value based on each deviation from a target weight and the target position of a centroid. SOLUTION: A product selecting device 2 selects a necessary product based on attributes such as an transporting destination, the data of delivery and a loading planning device 4 makes a plan for efficiently loading products in a pallet. Then in this case, what are obtained are the deviation of the total weight of the products loaded on a loaded facility from the target weight, the deviation of the position of the centroid of the loaded facility in the state of loading the products on the loaded facility from the target position of the centroid, the deviation of the position of the centroid of the loaded facility in the state of loading the products on the the loaded facility from the target position of the centroid concerning a first direction on the loaded facility and the evaluation value of the position of the centroid of the loaded facility in the state of loading the products concerning a second direction based on deviation from the target position of the centroid. Thus a plan close to a desired evaluation value is extracted from plural prepared and changed plans.

Device and method for removing noise in color image

Abstract: PROBLEM TO BE SOLVED: To provide a device and method for removing noise with which noise removal in a color image is enabled and the stability of color is improved as well. SOLUTION: This device performs noise removal by scanning the color image while using a filter composed of plural picture elements. At a certain time point, the pixel data of the color image concerning respective picture elements scanned by the filter are deveroped in a Lab uniform color space, centroid positions Ga and Gb in that distribution are found, and distances between these centroid positions Ga and Gb and the respective picture elements are calculated. Then, the discrete value of those distances is calculated, a number M is decided corresponding to the level of the discrete value, the picture element at a coordinate position closer to the centroid positions Ga and Gb the Mth is defined as a selective picture element, and the pixel data of that selected picture element are applied as the output of the filter.

Optimization of the Shape of Receiving Aperture in a Phase Doppler System

Abstract: The phase centroid of an aperture used in a phase/Doppler velocimeter (PDV) is introduced. It is defined as the point detector whose phase response is identical to the finite-area aperture of PDV. The phase centroid is fixed only for certain aperture shapes and certain particle size ranges. Guidelines are provided to obtain a spatially invariant phase centroid.

Image edge location estimate based on the image centroid slope

Abstract: A technique is developed for estimating the leading edge location of an imaged target based on the target's centroid and its slope as the raster is scanned across the target's image. Since the estimate involves more pixels than the standard edge algorithm is easily implemented in a pipe-line process so that the leading edge location can be determined as the video is being read off the focal plane array with minimum processing delay. This algorithm can be shown to be a generalization of the standard biased centroid track algorithm. However, while the biased centroid algorithm requires a priori knowledge of the imaged target shape in order to determine the propose bias, this algorithm estimates the shape dependent factors in real time without any a priori knowledge.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Partial-volume effect on marker localization in medical density images

Abstract: Registration of medical images to each other and to physical space for the purposes of surgical planning and surgical navigation can be accomplished using externally attached fiducial markers. The accuracy of fiducial localization, that is, the accuracy of estimating the position of the marker's centroid, is extremely important because marker-based registration accuracy is proportional to localization accuracy. The traditional method of calculating the marker centroid using intensity weighting contains a serious logic flaw. This paper introduces a novel and efficient method for correcting this flaw. Theoretical analysis, computer simulation, and analysis of clinical images demonstrate the importance of this correction.