Pixel patterns for voxels in a contact-type three-dimensional imaging system for full-parallax image display

Incomplete voxels, which can be seen only at a part of the viewing zone's cross section in the optical configuration of a full parallax multiview imaging system based on a two-dimensional point light source array, are identified. Their corresponding pixel patterns are found to maximize the space where the voxels can exist in the configuration and to increase the voxel resolution of the displayable three-dimensional images. Furthermore, the pixel patterns for the rhomb-shaped pixel cells are also defined, and some problems related to voxel-based image synthesis are discussed.     

Minimum-volume coil arrangements for generation of uniform magnetic fields

This paper describes an optimization method for designing electromagnetic coil arrangements that generate uniform magnetic fields. The method can accurately and efficiently determine an arrangement that minimizes the volume of the coils. An important advantage of the method is that the solutions it generates are guaranteed to be global minimums. The method may be useful for designing large superconducting magnets, since their cost depends strongly on the amount of superconducting wire required. It is also shown that the method can be applied to minimize the power consumption of resistive magnets.     

The new block pixel sort algorithm for TVC-encrypted medical image

To transfer the medical image from one place to another place or to store a medical image in a particular place with secure manner has become a challenge. In order to solve those problems, the medical image is encrypting and compressing before sending or saving at a place. In this paper, a new block pixel sort algorithm has been proposed for compressing the encrypted medical image. The encrypted medical image acts as an input for this compression process. During the compression, encrypted secret image E₁₂(;) is compressed by the pixel block sort encoding (PBSE). The image is divided into four identical blocks, similar to 2×2 matrix. The minimum occurrence pixel(s) are found out from every block and the positions of the minimum occurrence pixel(s) are found using the verdict occurrence process. The pixel positions are shortened with the help of a shortening process. The features (symbols and shortened pixel positions) are extracted from each block and the extracted features are stored in a particular place, and the values of these features put together as a compressed medical image. The next process of PBSE is pixel block short decoding (PBSD) process. In the decoding process, there are nine steps involved while decompressing the compressed encrypted medical image. The feature extraction value of compressed information is found out from the feature extraction, the symbols are split and the positions are shortened in a separate manner. The position is retrieved from the rescheduled process and the symbols and reconstructed positions of the minimum occurrence pixels are taken block wise. Every symbol is placed based on the position in each block: if the minimum occurrence pixel is ‘0’, then the rest of the places are automatically allocated as ‘1’ or if the minimum occurrence pixel is ‘1’ the remaining place is automatically allocated as ‘0’. Both the blocks are merged as per order 2×2. The final output is the reconstructed encrypted medical image. From this compression method, we can achieve the high compression ratio, minimum time, less compression size and lossless compression, which are the things experimented and proved.     

Color image generation of a three-dimensional object with rainbow holography and a one-wavelength laser

Based on conventional one-step true-color rainbow holography, a new true-color rainbow holography of a three-dimensional diffused object is presented. By means of conjugate reconstruction with a onewavelength laser of a master hologram recorded with three laser wavelengths, the hologram can be transferred to a single type of recording material with a single exposure to achieve true-color holographic display. Therefore a photoresist master can be produced for embossing copy.     

Liquid crystal-on-silicon implementation of the partial pixel three-dimensional display architecture

We report the implementation of a liquid crystal-on-silicon, three-dimensional (3-D) diffractive display based on the partial pixel architecture. The display generates multiple stereoscopic images that are perceived as a static 3-D scene with one-dimensional motion parallax in a manner that is functionally equivalent to a holographic stereogram. The images are created with diffraction gratings formed in a thin liquid crystal layer by fringing electric fields from transparent indium tin oxide interdigitated electrodes. The electrodes are controlled by an external drive signal that permits the 3-D scene to be turned on and off. The display has a contrast ratio of 5.8, which is limited principally by optical scatter caused by extraneous fringing fields. These scatter sources can be readily eliminated. The display reported herein is the first step toward a real-time partial pixel architecture display in which large numbers of dynamic gratings are independently controlled by underlying silicon drive circuitry.     

Breast ultrasound image improvement by pixel compounding of compression sequence

Pixel compounding is a technique that synthesizes the information of an image sequence involving slow decorrelation of the speckle to form a detail-recovered and speckle reduced image. To avoid extra data acquisition time and patient exposure, reuse of the existing data is desirable. In the procedure of elasticity imaging, a set of B-mode images with slight changes due to deformation is produced, which provides an ideal input for the pixel compounding. The improvement in image quality is evaluated quantitatively using a figure-of-merit (FOM) that indicates the quality of boundary information recovery and the contrast-to-noise ratio (CNR) over the phantom images. The increase in average CNR is from 0.4 in the original images to 0.8 in the pixel compounded images. The improvement in average FOM is from 0.15 to more than 0.5 on a scale of 0 to 1. In vivo results with a breast cyst, a fibroadenoma, and a breast cancer are also presented and the image quality improvement is subjectively evaluated. The results suggest that B-mode breast images from compression procedures are suitable data for pixel compounding, and that a speckle-reduced and detail-recovered or detail-maintained image can be produced. The improved imaging may provide alternative or better information for detection and diagnosis. A similar approach could be extended to elasticity imaging with other modalities.     

数字图像单个像元分形维数的特征与计算方法

通过分形理论把空间结构信息引入遥感分类中,必须解决分形维数计算的问题,为此提出了一种通过相邻像元间灰度值大小的变化计算数字图像单个像元分形维数的算法。选定计算窗口值 L 后,运用所编程序对 TM 遥感数据进行运算,并得到所需分维值数据。发现所得分维值随窗口值 L 增大而减小;大窗口值的分维值图像较抽象,但建议窗口值不超过 61;小窗口值的分维值图像较清晰,但窗口值不能小于 5。     

Error evaluation technique for three-dimensional digital image correlation

Three-dimensional (3D) digital image correlation (DIC) is one of the most popular techniques used in engineering for strain and deformation measurement. However, the error analysis of 3D DIC, especially which kind of parameters dominates the error of 3D coordinate reconstruction in any kind of configuration, is still under study. In this paper, a technique that can be used for error determination of reconstruction is presented. The influence from the system calibration and image correlation to the error is theoretically analyzed. From numerical experiments of one-dimensional line and two-dimensional plane, the evaluation procedure is validated to be flexible. A typical test with standard objects is also conducted. With this technique, once a 3D DIC system is set up and images of objects with speckles and calibration boards are recorded, the error of the configuration can be immediately evaluated. The standard deviation of every point in the world coordinate can be determined by statistical analysis.     

Optimum displacement for compound image generation in medical ultrasound

Incoherent averaging of measurements made at different look directions can be used to reduce speckle noise in medical ultrasound images. An analytic expression for the correlation between two measurements made at different spatial positions is derived. Using this expression, the optimum aperture displacement for efficient incoherent averaging (i.e. compounding) is computed and found to equal approximately one-half the aperture length.     

Optical image recognition of three-dimensional objects

A three-dimensional (3-D) optical image-recognition technique is proposed and studied. The proposed technique is based on two-pupil optical heterodyne scanning and is capable of performing 3-D image recognition. A hologram of the 3-D reference object is first created and then is used to modulate spatially one of the pupils of the optical system; the other pupil is a point source. A 3-D target object to be recognized is then scanned in two dimensions by optical beams modulated by the two pupils. The result of the two-dimensional scan pattern effectively displays the correlation of the holographic information of the 3-D reference object and that of the 3-D target object. A strong correlation peak results if the two pieces of the holographic information are matched. We analyze the proposed technique and thereby lay a theoretical foundation for optical implementations of the idea. Finally, computer simulations are performed to verify the proposed idea.     

Exploitation of image coherency and topology preservation to accelerate the pixel mapping stage of SOM-based image quantisation

Abstract

SOM-based image quantisation requires a considerable amount of processing time even during the pixel mapping stage. Basically, a full search algorithm is employed to find a codeword, within a codebook, whose distance to the queried pixel is minimum. In this paper, we present a novel approach to accelerate the pixel mapping stage by utilisation of the spatial redundancy of pixels in the image and the inherent topological preservation nature of the resulting codebook. The experimental results confirm that the proposed approach outperforms ordinary solutions and is comparable to state-of-the-art solutions in terms of execution time. In addition, as the proposed approach does not require codebook sorting and a complex data structure with variable sizes, this simplifies its implementation and makes it feasible for hardware realisation.     

Automatic generation of octree-based three-dimensional discretizations for Partition of Unity methods

The Partition of Unity Method (PUM) can be used to numerically solve a set of differential equations on a domain Ω. The method is based on the definition of overlapping patches Ω _i comprising a cover {Ω _i } of the domain Ω. For an efficient implementation it is important that the interaction between the patches themselves, and between the patches and the boundary, is well understood and easily accessible during runtime of the program. We will show that an octree representation of the domain with a tetrahedral mesh at the boundary is an efficient means to provide the needed information. It subdivides an arbitrary domain into simply shaped topological objects (cubes, tetrahedrons) giving a non-overlapping discrete representation of the domain on which efficient numerical integration schemes can be employed. The octants serve as the basic unit to construct the overlapping partitions. The structure of the octree allows the efficient determination of patch interactions.     

Delaunay versus max-min solid angle triangulations for three-dimensional mesh generation

The Delaunay triangulation has been used in several methods for generating finite element tetrahedral meshes in three-dimensional polyhedral regions. Other types of three-dimensional triangulations are possible, such as a triangulation satisfying a local max-min solid angle criterion. In this paper, we present experimental results to show that max-min solid angle triangulations are better than Delaunay triangulations for finite element tetrahedral meshes, since the former type of triangulations contains tetrahedra of better shape than the latter type. We also describe how mesh points are generated and triangulated in our tetrahedral mesh generation method.     

In situ calibration for wide-angle, three-dimensional stereoscopic image analysis

Accurate measurement of three-dimensional object coordinates from stereoscopic images is an essential element in various applications that require three-dimensional position information. Conventionally, optical ray tracing has been the measurement method of choice. However, it requires accurate knowledge of geometrical and optical parameters, such as the image distance, camera locations relative to the object field, and size, shape, and refractive index of intervening elements, such as apparatus windows. On the other hand, all these parameters need not be known if an optical transformation method based on an in situ calibration experiment is used. Furthermore, the use of in situ calibration not only increases the effective accuracy of the measured three-dimensional object coordinates but also reduces significantly the computational time compared with conventional optical ray tracing. The computational efficiency of the technique used is essential, especially when the application requires multiple determinations of a large number of three-dimensional coordinates, such as is the case with three-dimensional particle-tracking velocimetry. The basic concept and formulation of an optical transformation method based on an in situ calibration experiment is introduced. The technique is first demonstrated with synthetic data, then case studies with actual in situ calibration data are discussed.     

Digital shearing method for three-dimensional data extraction in holographic particle image velocimetry

We report a new digital shearing method for extracting the three-dimensional displacement vector data from double-exposure holograms. With this method we can manipulate both the phase and the amplitude of the recorded signal, which, like optical correlation analysis, is inherently immune to imaging aberration. However, digital shearing is not a direct digital implementation of optical correlation, and a considerable saving in computation time results. We demonstrate the power of the method by MATLAB simulation and discuss its performance with reference to optical analysis.     

Periodic three-dimensional mesh generation for crystalline aggregates based on Voronoi tessellations

In this paper a method for the generation of three-dimensional periodic meshes for the numerical simulation of polycrystalline aggregates is presented. The mesh construction is based on Voronoi and Hardcore Voronoi tessellations of random point seeds. Special emphasis is paid on the periodicity of the mesh topologies which leads to favorable numerical properties for the determination of effective properties using unit cells. The mesh generation algorithm is able to produce high quality meshes at low computational costs. Based on unit cell simulations with different but statistically equivalent microstructures, the effective linear elastic properties of polycrystals consisting of grains with a cubic symmetry are determined. The numerical results are compared with first-, third- and fifth-order bounds and experimental data. Numerical simulations show the efficiency of the proposed homogenization technique.     

Real-time pickup method for a three-dimensional image based on integral photography

We studied integral photography (IP), which creates three-dimensional autostereoscopic images. In particular we studied the possibility of a new method that uses a television camera to shoot directly numerous real images produced by a lens array. Unlike the conventional IP method in which the film is placed immediately behind a lens array, this method employs a television camera, which enables us to shoot moving pictures. Of a number of factors affecting the process of image pickup, we examined some optical factors and compared them with those obtained by the conventional IP method. The results show that with this new direct pickup method that uses a television camera, we can obtain an IP image like those obtained by using the conventional IP method. Further, we conducted an experiment with an high-definition TV camera, confirming the production of an autostereoscopic image by using a display device that combines a liquid-crystal panel and pinholes.     

A morphing method for shape generation and image prediction in product design

A shape morphing and image prediction method for product design is proposed in this article, in which a feature-based method is first used to construct 3-D CAD models of a product, then new shapes are generated with a shape morphing method and the images of the morphed shapes are analyzed using modified gray theory with Fourier residual correction. With the aid of this model, the designer can quickly obtain a product form and its corresponding image to help him/her to design the required product. Though LCD monitor design is applied, this method can also be used to develop other products.