Abstract: The wavefront-sensor is one of the most important components of any adaptive optics (AO) system. The simplicity of the Shack-Hartmann sensor has made it a popular choice for such systems. Its accuracy, which largely determines its performance depends on having a good and robust centroid algorithm. Despite a large number of studies, the general recipe for selecting the best centroiding algorithm and best pixel size in a Shack-Hartmann wavefront sensor is still lacking. We combine analytical theory with numerical simulations to compare various flavors of centroiding algorithms (thresholding, windowing, correlation, quad-cell) under different conditions of photon flux, read-out noise, and sampling. It is shown that the choice of the best method depends on those parameters. At very low signal to noise ratio, the performance of the quad-cell is close to optimum.

Abstract: The shape of aggregates has an important influence on the behavior of civil engineering materials. Digital imaging techniques provide unique opportunities for describing these features in an automated fashion. Shape analysis of fine and coarse aggregate particles is investigated in this study using Fourier transform of digital images. The geometric signature of each shape is extracted by measuring the distance between its centroid and the boundary at constant increment of angles, and Fourier transforms are used to evaluate its spectral information. The number of highest amplitude harmonics required for accurate profile regeneration is evaluated. Shape of a given aggregate particle is reconstructed using inverse Fourier transforms considering a limited number of significant harmonics. A parameter that can quantify the error between regenerated and original profiles is proposed. Using this value, two shape parameters are defined to describe the overall shape and the ruggedness of a particle. A procedure of quantitatively describing the roundness/angularity of aggregate shape is presented and extended to three dimensions using orthogonal views.

Abstract: A method for measuring the range to multiple points on a surface by projecting a line of light onto the surface, imaging said line of light onto an XY photodetector array at an oblique angle, reading out the array one line at a time, computing the centroid of said line of light on each Y line across X columns as each line is read out of the array in onboard FPGA (Field Programmable Gate Array) or similar real time logic, computing quality factors for each computed centroid and encoding this as one or more bits in the centroid value, transmitting said tagged centroid to a local or remote data receiver, and computing the range to the surface for each point corresponding to each centroid using a previous calibration step.

Abstract: In this paper, a novel boundary based corner detection algorithm is proposed. The proposed algorithm is computationally fast and efficient. The proposed method computes an expected point for every point on a boundary curve. An expected point corresponding to a point on the boundary curve is defined to be the geometrical centroid of the symmetrical boundary segment of size 2k+1, for some integer k>0, within the neighborhood of the point in consideration. A new 'cornerity' index for a point on the boundary curve is defined to be the distance between the point and its corresponding expected point. The larger the cornerity index, the stronger is the evidence that the boundary point is a corner point. A set of rules is worked out to guide the process of locating true corner points. The conducted experiments establish that the proposed approach is invariant to image transformations viz., rotation, translation and scaling.

Abstract: Nonlinear normalization (NLN) based on line density equalization has been widely used in handwritten Chinese character recognition (HCCR). Our previous results showed that global transformation methods, including moment normalization and a newly proposed bi-moment method, generate smooth normalized shapes at lower computation effort while yielding comparable recognition accuracies. This paper proposes a new global transformation method, named modified centroid-boundary alignment (MCBA) method, for HCCR. The previous CBA method can efficiently correct the skewness of centroid by quadratic curve fitting but fails to adjust the inner density. The MCBA method adds a simple trigonometric (sine) function onto quadratic function to adjust the inner density. The amplitude of the sine wave is estimated from the centroids of half images. Experiments on the ETL9B and JEITA-HP databases show that the MCBA method yields comparably high accuracies to the NLN and bi-moment methods and shows complementariness.

Abstract: It is shown that the discrepancy between path integral Monte Carlo [M. Zoppi et al., Phys. Rev. B 65, 092204 (2002)] and path integral centroid molecular dynamics [F. J. Bermejo et al., Phys. Rev. Lett. 84, 5359 (2000)] calculations of the static structure factor of liquid para-hydrogen can be explained based on a deconvolution equation connecting centroid and physical radial distribution functions. An explicit expression for the kernel of the deconvolution equation has been obtained using functional derivative techniques. In the superposition approximation, this kernel is given by the functional derivative of the effective potential with respect to the pairwise classical potential. Results of path integral Monte Carlo calculations for the radial distribution function and the static structure factor of liquid para-hydrogen are presented.

Abstract: We describe a noncontact test procedure with which to obtain the shapes of fast convex surfaces. For this, an array of sources is positioned in a straight line and separated in such a way that the image by reflection on the surface consists of a set of equally spaced bright spots. By rotating the surface, we test different meridians such that, after 360°, the entire surface is measured. We present the source array design and the surface evaluation algorithm. We found that, to reduce numerical error in the evaluation of the shape of the surface, a numerical integration must be performed by a method that uses parabolic arcs instead of the traditional method that uses trapezoids. Through some numerical simulations we analyzed the accuracy of the method by introducing random displacements into the measured data. We found that to measure the quality of the surface with accuracy better than 5 μm, we have to measure the coordinates of the centroids on the image plane with an accuracy better than 0.5 pixel, and we to have measure the positions of the linear sources with an accuracy better than 0.5 mm. Experimental results for the testing of a carbon fiber convex sphere of 383.6-mm diameter (f/0.398) are shown.

Abstract: We investigate the geometric properties of simplices in Euclidean d-dimensional space for which two or more of the analogues of the classical triangle centers (including the centroid, circumcenter, incenter, orthocenter or Monge point, and the Fermat-Torricelli point) coincide. We also investigate the geometric significance of the cevian line segments through a given center having the same length. We give a unified presentation, including known results for d=2 and d=3.

Abstract: Spectroastrometry is a technique which has the potential to resolve flux distributions on scales of milliarcseconds. In this study, we examine the application of spectroastrometry to binary point sources which are spatially unresolved due to the observational point spread function convolution. The technique uses measurements with sub-pixel accuracy of the position centroid of high signal-to-noise long-slit spectrum observations. With the objects in the binary contributing fractionally more or less at different wavelengths (particularly across spectral lines), the variation of the position centroid with wavelength provides some information on the spatial distribution of the flux. We examine the width of the flux distribution in the spatial direction, and present its relation to the ratio of the fluxes of the two components of the binary. Measurement of three observables (total flux, position centroid and flux distribution width) at each wavelength allows a unique separation of the total flux into its component parts even though the angular separation of the binary is smaller than the observations' point-spread function. This is because we have three relevant observables for three unknowns (the two fluxes, and the angular separation of the binary), which therefore generates a closed problem. This is a wholly different technique than conventional deconvolution methods, which produce information on angular sizes of the sampling scale. Spectroastrometry can produce information on smaller scales than conventional deconvolution, and is successful in separating fluxes in a binary object with a separation of less than one pixel. We present an analysis of the errors involved in making binary object spectroastrometric measurements and the separation method, and highlight necessary observing methodology.

Abstract: We propose a node centroid method with Hill-Climbing to solve the well-known matrix bandwidth minimization problem, which is to permute rows and columns of the matrix to minimize its bandwidth. Many heuristics have been developed for this NP-complete problem including the Cuthill-McKee (CM) and the Gibbs, Poole and Stockmeyer (GPS) algorithms. Heuristics such as simulated annealing, tabu search and GRASP have been used, where tabu search and the GRASP with path relinking have achieved significantly better solution quality than the CM and GPS algorithms. Experimentation shows that the node centroid method achieves the best solution quality when compared with these while being much faster than the newly-developed algorithms. Also, the new algorithm achieves better solutions than the GPS algorithm in comparable time.

Abstract: A pixel center position that is not covered by a primitive covering a portion of the pixel is displaced to lie within a fragment formed by the intersection of the primitive and the pixel. X,y coordinates of a pixel center are adjusted to displace the pixel center position to lie within the fragment, affecting actual texture map coordinates or barycentric weights. Alternatively, a centroid sub-pixel sample position is determined based on coverage data for the pixel and a multisample mode. The centroid sub-pixel sample position is used to compute pixel or sub-pixel parameters for the fragment.

Abstract: A method of dividing an image into grid regions for the application of a watermark or fingerprint uses a calculation of centroid of the image to centre the grid and uses centroids of portions of the image to set the size of the grid.

Abstract: The present invention is directed to an image tracking system that tracks the motion of an object. The image processing system tracks the motion of an object with an image recording device that records a first image of an object to be tracked and shortly thereafter records a second image of the object to be tracked. The system analyzes data from the first and the second images to provide a difference image of the object, defined by a bit map of pixels. The system processes the difference image to determine a threshold and calculates a centroid of the pixels in the difference image above the threshold. The system then determines the center of the difference image and determines a motion vector defined by the displacement from the center to the centroid and determines a pan tilt vector based on the motion vector and outputs the pan tilt vector to the image recording device to automatically track the object.

Abstract: The centroid molecular dynamics (CMD) method is extended to the rotational motion of rigid bodies. An algorithm is developed that homogeneously samples the orientational neighbourhood associated with the quantum degrees of freedom of a specified orientational centroid and by design ensures the constancy of the centroid. As part of this development a general definition for an orientational centroid (or average rotation), as well as a procedure to determine it, are presented. The application of this CMD methodology in quantum simulations of rigid body systems is discussed and demonstrated for a simple system.

Abstract: A real-time VLSI optical centroid processor has been developed as part of a larger Shack-Hartmann wavefront sensor system for applications in adaptive optics. The implementation of the optical centroid detection system was demonstrated successfully using a hardware emulation system. Subsequently, the design has been implemented as a CMOS single-chip solution. This has advantages in terms of speed, power consumption, system size, and cost. The design of the different components of the system will be discussed along with test results of the fabricated device.

Abstract: Recently, thermal imaging has been receiving much attention owing to its application to face recognition in rapid mass fever detection. However, a non-frontal view of the face captured by the camera leads to erroneous temperature measurements. The paper proposes an automated thermal imaging system that is able to discriminate frontal from non-frontal face views with the assumption that at any one time, there is only one person in the field of view of the camera and no other heat-emitting objects are detected by the camera. The relationship between temperature and grey level values, various methods of enhancement, restoration, and segmentation of infrared images, and a way to determine the pose of a face are explained. A boundary signature, i.e. distance from centroid (DFC) of the human face to the lower part of the face outline is used. This measure has been used for the representation of objects, but it is now used to compare the degree of symmetry of the lower face outline. Experimental results are given to verify the validity of the method.

Abstract: We start from an algorithm for on-line linear hierarchical classification for multidimensional data, using a centroid aggregation criterion. After evoking some real-life on-line settings where it can be used, we analyze it mathematically, in the framework of the Lance–Williams algorithms, proving that it does not have some useful properties: it is not monotonic, nor space-conserving. In order to use its on-line capabilities, we modify it and show that it becomes monotonic. While still not having the internal similarity-external dissimilarity property, the worst case classifications of the new algorithm are correctable with an additional small computational effort, on the overall taking O(n⋅k) time for n points and k classes. Experimental study confirm the theoretical improvements upon the initial algorithm. A theoretical and experimental comparison to other algorithms from the literature, shows that it is among the fastest and performs well.

Abstract: Due to increasing demand on deployable surveillance systems in recent years, object tracking and activity recognition are receiving considerable attention in the research community. This thesis contributes to both the tracking and the activity recognition components of a surveillance system. In particular, for the tracking component, we propose two different approaches for tracking objects in video acquired by mobile cameras, each of which uses a different object shape representation. The first approach tracks the centroids of the objects in Forward Looking Infrared Imagery (FLIR) and is suitable for tracking objects that appear small in airborne video. The second approach tracks the complete contours of the objects, and is suitable for higher level vision problems, such as activity recognition, identification and classification. Using the contours tracked by the contour tracker, we propose a novel representation, called the action sketch, for recognizing human activities. Object tracking in airborne imagery. Images obtained from an airborne vehicle generally appear small and can be represented by geometric shapes such as circle or rectangle. After detecting the object position in the first frame, the proposed object tracker models the intensity and the local standard deviation of the object region defined by the shape model. It then tracks the objects by computing the mean-shift vector that minimizes the distance between the kernel distribution for the hypothesized object and its prior. Contour tracker. Contour tracking is performed by evolving an initial contour toward the correct object boundaries based on discriminant analysis, which is formulated as a variational calculus problem. Once the contour is initialized, the method generates an online shape model for the object along with the color and the texture priors for both the object and the background regions. A priori texture and color PDFs of the regions are then fused based on the discrimination properties of the features between the object and the background models. Behavior analysis. We propose a novel approach to represent human actions by modeling the dynamics (motion) and the structure (shape) of the objects in video. Both the motion and the shape are modeled using a compact representation, which is called the “action sketch”. An action sketch is a view invariant representation obtained by analyzing important changes that occur during the motion of the objects. When an actor performs an action in 3D, the points on the actor generate space-time trajectories in four dimensions (x, y, z, t). Projection of the world to the imaging coordinates converts the space-time trajectories into the spatio-temporal trajectories in three dimensions (x, y, t). (Abstract shortened by UMI.)

Abstract: The basic principle of star sensor was introduced. The characteristic of the star image were analysed. The methods of the threshold and the rectangle centroid for the star locating of the star image are researched with the characteristic of star image. They are based on the ways of theory and practice. The suitable arithmetic of star locating was confirmed. The star sensor has used this method to do star-locating deteetion and obtain satisfied results.

Abstract: Local buckling is a major consideration in the design of slender sections. The main effect of local buckling is to cause a redistribution of the longitudinal stress in which the greatest portion of the load is carried near the plate junctions. The redistribution produces increased stresses near the plate junctions and high bending stresses as a result of plate flexure, leading to ultimate loads below the squash load of the section. In singly symmetric cross-sections, the redistribution of longitudinal stress caused by local buckling also produces a shift of the line of action of the internal force (shift of effective centroid). The fundamentally different effects of local buckling on the behaviour of pin-ended and fixed-ended singly symmetric columns lead to inconsistencies in traditional design approaches. The paper describes local buckling and shift of effective centroid of slender sections. Tests of cold-formed steel channel columns have been described. The experimental local buckling loads were compared with the theoretical local buckling loads obtained using an elastic finite strip buckling analysis. The shift of the effective centroid was compared with the shift predicted using the Australian/New Zealand and American specifications for cold-formed steel structures.

Abstract: PROBLEM TO BE SOLVED: To provide a method and device for exposure control, which can reduce the processing loads SOLUTION: The method and device comprise a histogram creating means 2 for creating a histogram of the values of each pixel of an imaging device C, which is equipped with an image sensor having a plurality of pixels and can adjust exposure; a histogram edge removing means 3 for removing parts of the histogram; a centroid calculation means 4 for calculating the centroid of the histogram; a comparison means 5 for calculating the direction and the size of the shifting of the histogram's centroid from a predetermined reference range; and an exposure control means 6 for controlling the exposure so that the centroid falls within the reference range, based on the direction and size calculation Since the frequencies of the operations required for calculating the centroid can be made fewer than those required for calculating the average value of pixel output for one screen, processing loads can be reduced, as compared with the case where the average value of pixel output for one screen is used for control COPYRIGHT: (C)2004,JPO

Abstract: We present a new centroid computation circuit with very low dc offset and high bandwidth. A novel test setup is also shown to test adaptive optic integrated circuits. Static and dynamic simulation and test results of the centroid computation circuit are shown. Compared to the work of Deweerth we report a 4.3 times increase in the bandwidth in both simulation and test results. The centroid circuit is fabricated in the AMI 0.5 /spl mu/m CMOS process. A 1D centroid circuit with 7 photodiodes has dimensions equal to 765 /spl mu/m/spl times/90 /spl mu/m.

Abstract: The cross-section of a laser beam is almost impossible of a perfect circular shape; without doubting most of the cross-sections of laser beams are nearly in ellipse-like form. Therefore, by using an ellipse-like laser beam cross-section for underwater range finding, we are really interested in understanding the quality of range finding with different peak detection algorithms. According to our previous results, we found that the peak detection algorithm of illumination center is good for estimating the location of the laser spot in the image. However, background noise is still a serious problem while selecting a square of pixels for centroid calculation. In this paper, we modified the illumination center to a different algorithm which introduces the technique of the principal component analysis (PCA) to the centroid calculation. This algorithm restricts the selection of pixels to a region within an ellipse for centroid calculation. According to the results of range finding, we found that the ranging quality achieved by using the algorithm of the modified illumination center is much better than that obtained by using the algorithm of the illumination center. Therefore, the algorithm of the modified illumination center is proved to be effective to reduce the effect of background noise on range finding. Also, this result demonstrates that the way of selecting effective pixels for centroid calculation plays an important role.

Abstract: Selection of tracking algorithm is a critical aspect related to performance of video tracker. With the advancement in reconfigurable technology such as FPGAs, it is possible to analyse algorithms on hardware platform for real time implementation. A centroid based tracker has been developed using standard CCIR-B video from either CCD or IR camera. In the present work scheme for implementation of centroid tracker and VLSI architecture for various types of centroid based tracking algorithms has been analyzed. Xilinx FPGA has been used as a target device for performance evaluation of various centroid tracking algorithms and comparison of resource & timing requirements associated with these algorithms have been done.