Showing papers by "Yongtian Wang published in 2013"

Reducing the memory usage for effective computer-generated hologram calculation using compressed look-up table in full-color holographic display.

Abstract: A fast algorithm with low memory usage is proposed to generate the hologram for full-color 3D display based on a compressed look-up table (C-LUT). The C-LUT is described and built to reduce the memory usage and speed up the calculation of the computer-generated hologram (CGH). Numerical simulations and optical experiments are performed to confirm this method, and several other algorithms are compared. The results show that the memory usage of the C-LUT is kept low when number of depth layers of the 3D object is increased, and the time for building the C-LUT is independent of the number of depth layers of the 3D object. The algorithm based on C-LUT is an efficient method for saving memory usage and calculation time, and it is expected that it could be used for realizing real-time and full-color 3D holographic display in the future.

3D dynamic holographic display by modulating complex amplitude experimentally.

Abstract: Complex amplitude modulation method is presented theoretically and performed experimentally for three-dimensional (3D) dynamic holographic display with reduced speckle using a single phase-only spatial light modulator. The determination of essential factors is discussed based on the basic principle and theory. The numerical simulations and optical experiments are performed, where the static and animated objects without refinement on the surfaces and without random initial phases are reconstructed successfully. The results indicate that this method can reduce the speckle in reconstructed images effectively; furthermore, it will not cause the internal structure in the reconstructed pixels. Since the complex amplitude modulation is based on the principle of phase-only hologram, it does not need the stringent alignment of pixels. This method can be used for high resolution imaging or measurement in various optical areas.

Automatic vasculature identification in coronary angiograms by adaptive geometrical tracking.

Abstract: As the uneven distribution of contrast agents and the perspective projection principle of X-ray, the vasculatures in angiographic image are with low contrast and are generally superposed with other organic tissues; therefore, it is very difficult to identify the vasculature and quantitatively estimate the blood flow directly from angiographic images. In this paper, we propose a fully automatic algorithm named adaptive geometrical vessel tracking (AGVT) for coronary artery identification in X-ray angiograms. Initially, the ridge enhancement (RE) image is obtained utilizing multiscale Hessian information. Then, automatic initialization procedures including seed points detection, and initial directions determination are performed on the RE image. The extracted ridge points can be adjusted to the geometrical centerline points adaptively through diameter estimation. Bifurcations are identified by discriminating connecting relationship of the tracked ridge points. Finally, all the tracked centerlines are merged and smoothed by classifying the connecting components on the vascular structures. Synthetic angiographic images and clinical angiograms are used to evaluate the performance of the proposed algorithm. The proposed algorithm is compared with other two vascular tracking techniques in terms of the efficiency and accuracy, which demonstrate successful applications of the proposed segmentation and extraction scheme in vasculature identification.

A high‐efficiency holographic waveguide display system with a prism in‐coupler

Abstract: Holographic waveguide display system with high efficiency is presented by embedding an in-coupling prism and an out-coupling reflective volume holographic element, which enables a small- type configuration The improved coupling scheme can achieve 25% efficiency and the chromatic is corrected properly

A Super Lens System for Demagnification Imaging Beyond the Diffraction Limit

Abstract: A super lens system is proposed to achieve subdiffraction limit demagnification imaging. The super lens system consists of a hyperlens with planar input and output surfaces, a metal superlens, and a plasmonic reflector. By employing the hyperlens to transform evanescent waves into propagating waves and employing the metal superlens and the plasmonic reflector to amplify evanescent waves, the super lens system can produce a subdiffraction limit image with relatively high electric field intensity. The reduction factor of the super lens system depends on the geometric parameters of the hyperlens. Simulation results show that an image with a half-pitch resolution of about one tenth the operating wavelength and a reduction factor of about 2.2 can be produced by the super lens system. The proposed super lens system has potential applications in nanolithography.

Survey on brain tumor segmentation methods

Abstract: The segmentation of brain tumor using Magnetic Resonance Image (MRI) plays an important role in the medical image process. This paper presents a comprehensive survey on brain tumor methods and technology using MRI images. Generally, brain tumor segmentation methods can divided into two main categories, spatial continuous and spatial discrete methods. Several methods, techniques, related advantage and weakness will be described and discussed. The evaluation measures are mentioned and the qualities of different method focus on the methods that were applied on the standard data sets. The efficient and stably brain tumor segmentation is still a challenging task for the unpredictable appearance and shape of the brain tumor.

Fast and automatic ultrasound simulation from CT images.

Abstract: Ultrasound is currently widely used in clinical diagnosis because of its fast and safe imaging principles. As the anatomical structures present in an ultrasound image are not as clear as CT or MRI. Physicians usually need advance clinical knowledge and experience to distinguish diseased tissues. Fast simulation of ultrasound provides a cost-effective way for the training and correlation of ultrasound and the anatomic structures. In this paper, a novel method is proposed for fast simulation of ultrasound from a CT image. A multiscale method is developed to enhance tubular structures so as to simulate the blood flow. The acoustic response of common tissues is generated by weighted integration of adjacent regions on the ultrasound propagation path in the CT image, from which parameters, including attenuation, reflection, scattering, and noise, are estimated simultaneously. The thin-plate spline interpolation method is employed to transform the simulation image between polar and rectangular coordinate systems. The Kaiser window function is utilized to produce integration and radial blurring effects of multiple transducer elements. Experimental results show that the developed method is very fast and effective, allowing realistic ultrasound to be fast generated. Given that the developed method is fully automatic, it can be utilized for ultrasound guided navigation in clinical practice and for training purpose.

Modulation of optical intensity on curved surfaces and its application to fabricate DOEs with arbitrary profile by interference

Abstract: We demonstrate a novel method for the modulation of the optical intensity on curved surfaces (CS) by interference and apply it to fabricate diffractive optical elements (DOEs) with arbitrary profile and large area on CS. The intensity on CS is modulated accurately by two phase distributions. Both a binary pattern and a gray pattern are reconstructed numerically on the lens surfaces with big curvatures in large areas, while a binary and non-periodic pattern is produced experimentally on a lens surface with a radius of curvature in 25.8 mm. The simulations together with the experiment demonstrate the validity of the method. To our knowledge, it is the first time to present an approach for fabricating DOEs with arbitrary profile and large area on CS by interference.

Rigid registration of 3-D medical image using convex hull matching

Abstract: In this paper, a robust approach called convex hull matching (CHM) technique is proposed for registration of medical images that differ from each other with Euclidean transformation. Firstly, point sets on the surface of the medical image are extracted, and then the 3-D convex hull is constructed from the point sets and triangle patches on the surface of convex hulls are specified by predefining their normal vectors. Secondly, each edge of the referenced triangle is compared with all the edges of the triangle in other point set to find the congruent pair set and also to obtain the scaling factor. Thereafter, the transformation parameters of each triangle pairs including rotation and translation are optimized by minimizing the Euclidian distance between the corresponding vertex pairs. Hence, rigid transformation of the two point sets is obtained by iteratively enumerating and evaluating similarity measures of the triangle patches chosen. Global optimization is achieved through RANSAC optimization by removing the correspondence pairs that may lead to large matching errors of the whole point sets. The experiments evaluate the performance of the proposed algorithm on simulated data with the presence of outliers and noise. The results show the efficiency of CHM by quantitative analysis and comparative study with existing approaches like EM-ICP, LM-ICP and 4PCS. Finally, the real clinical data experiments confirm the proposed algorithm is a strong performer in medical image registration.

Overview of fast algorithm in 3D dynamic holographic display

Abstract: 3D dynamic holographic display is one of the most attractive techniques for achieving real 3D vision with full depth cue without any extra devices. However, huge 3D information and data should be preceded and be computed in real time for generating the hologram in 3D dynamic holographic display, and it is a challenge even for the most advanced computer. Many fast algorithms are proposed for speeding the calculation and reducing the memory usage, such as:look-up table (LUT), compressed look-up table (C-LUT), split look-up table (S-LUT), and novel look-up table (N-LUT) based on the point-based method, and full analytical polygon-based methods, one-step polygon-based method based on the polygon-based method. In this presentation, we overview various fast algorithms based on the point-based method and the polygon-based method, and focus on the fast algorithm with low memory usage, the C-LUT, and one-step polygon-based method by the 2D Fourier analysis of the 3D affine transformation. The numerical simulations and the optical experiments are presented, and several other algorithms are compared. The results show that the C-LUT algorithm and the one-step polygon-based method are efficient methods for saving calculation time. It is believed that those methods could be used in the real-time 3D holographic display in future.

26.3: Volumetric Display System Using Multiple Mini‐Projectors

Abstract: A new type of volumetric display is developed using multiple mini-projectors and a rotating screen. A novel illumination subsystem is designed to ensure accurate synchronization between the projectors and the rotating screen. Therefore, low-speed and low-cost miniature display devices can be used in the mini-projectors to realize dynamic volumetric imaging with full color and high resolution.

Robust structure from motion with affine camera via low-rank matrix recovery

Abstract: We present a novel approach to structure from motion that can deal with missing data and outliers with an affine camera. We model the corruptions as sparse error. Therefore the structure from motion problem is reduced to the problem of recovering a low-rank matrix from corrupted observations. We first decompose the matrix of trajectories of features into low-rank and sparse components by nuclear-norm and l 1-norm minimization, and then obtain the motion and structure from the low-rank components by the classical factorization method. Unlike pervious methods, which have some drawbacks such as depending on the initial value selection and being sensitive to the large magnitude errors, our method uses a convex optimization technique that is guaranteed to recover the low-rank matrix from highly corrupted and incomplete observations. Experimental results demonstrate that the proposed approach is more efficient and robust to large-scale outliers.

Image distance shift effect of the metal superlens and its applications to photolithography

Abstract: We show an image distance shift effect of the metal superlens, which is that in the case in which the pattern of a mask acting as an object and the distance from the mask to a given metal superlens are fixed, the image distance of the given metal superlens is shifted to larger values with decreasing the thickness of the mask or increasing the dielectric constant of the filling material in the slits of the mask. A possible explanation of this effect is proposed. Furthermore, simulation results show that, by using the reported effect, the performance of the metal superlens lithography technique assisted by a plasmonic mirror can be significantly improved.

Energy back-projective composition for 3-D coronary artery reconstruction

Abstract: This paper presents a novel energy back-projective composition model (EBPCM) for 3-D reconstruction of the coronary arteries from two mono-plane angiographic images. A major problem with the commonly used parameter deformable model is that the predefined correspondences may become non-strict matching after the curve evolution, which generally leads to large extra calculation errors. In this study, the energy field in the image is back-projected to 3-D space and decomposed into three independent components in the world coordinates centered at the iso-center of the C-arm. Then, the components from different views are composited together according to the rotation and scaling relationship of the imaging angles. The composited energy field hence is utilized as the external force to control the evolution of the vascular structure in 3-D space. As the driving force is iteratively updated according to energy in the two projection images, the non-strict matching can be effectively avoided. Also, the proposed method is very flexible, which can be composited with any energy fields such as Generalized Gradient Vector Flow (GGVF) and Potential Energy (PE) etc. Experiments demonstrate that the proposed method is very effective and robust, when using GGVF as the external force, the reconstruction RMS error can be reduced to about 0.595mm in the 3-D space.

Outdoor scenes identification on mobile device by integrating vision and inertial sensors

Abstract: This paper addresses the identification of large scale outdoor scenes on smart phone by fusing outputs of inertial sensors and computer vision techniques. The main contributions can be summarized as follows: Firstly, we propose an overlap region divide (ORD) method to plot image position area, which is fast enough to find the nearest visiting area and can also reduce the search range compared with the traditional approaches. Secondly, the vocabulary tree based approach is improved by introducing fast geometric consistency constraints (FGCC). Our method involves no operation in the high-dimensional feature space and does not assume a global transform between a pair of images. Thus, it substantially reduces the computational complexity and memory usage, which makes the city scale image recognition feasible on the smartphone. Experiments on a collected database including 0.16 million images show that the proposed method demonstrates excellent identification performance, while maintaining the average identification time of less than 1s.

Advances in Image and Graphics Technologies

Abstract: Automatic, fast and accurate extraction of the blood vessel is an important task in the image-aided diagnosis of disease. In this paper, we describe a novel superficial vessel imaging and projecting system. First, the superficial vessel of human arm is captured by NIR imaging technique, and then three pre-processing algorithms, including hair removal, non-uniform illumination correction and vessel enhancement, are developed to strengthen the vessel image. Second, a model-based binarization method is proposed to detect vessel-like structures. And then the mathematic morphological and connected component refinement methods are integrated to remove small vessel noises. Experimental results demonstrate that our system can imaging superficial vessels on real-time. The proposed system does not need any human interaction, which hence can be used in clinical venipuncture practices.

Global optimization of optimal angiographic viewing angles for coronary arteries with multiple segments

Abstract: For angiographic images, different imaging angles may lead to different degrees of foreshortening and overlap, which hence considerably interferes with the angiogram based diagnosis of vascular diseases In this study, a composite optimization method is proposed to determine the optimal viewing angle of angiograms, which can fully considerate stenosis and the interference caused due to multiple vascular segments In order to obtain the optimal angle for segments at multiple branches' intersection, a hyper plane optimization method is proposed to separate the relative branches The optimal angle for stenosis is designed by minimizing area of the projections of the vascular segments The multiple segments and the stenosis optimization are integrated with the foreshortening and overlap, which can hence give a more objective viewing angle of the coronary arteries from angiographic images Experimental results demonstrate that the proposed method is very effective and robust for optimizing the projection angle

A green-color portable waveguide eyewear display system

Abstract: Waveguide display systems are widely used in various display fields, especially in head mounted display. Comparing with the traditional head mounted display system, this device dramatically reduce the size and mass. However, there are still several fatal problems such as high scatting, the cumbersome design and chromatic aberration that should be solved. We designed and fabricated a monochromatic portable eyewear display system consist of a comfortable eyewear device and waveguide system with two holographic gratings located on the substrate symmetrically. We record the gratings on the photopolymer medium with high efficiency and wavelength sensitivity. The light emitting from the micro-display is diffracted by the grating and trapped in the glass substrate by total internal reflection. The relationship between the diffraction efficiency and exposure value is studied and analyzed, and we fabricated the gratings with appropriate diffraction efficiency in a optimization condition. To avoid the disturbance of the stray light, we optimize the waveguide system numerically and perform the optical experiments. With this system, people can both see through the waveguide to obtain the information outside and catch the information from the micro display. After considering the human body engineering and industrial production, we design the structure in a compact and portable way. It has the advantage of small-type configuration and economic acceptable. It is believe that this kind of planar waveguide system is a potentially replaceable choice for the portable devices in future mobile communications.

Optomechanical design and analysis with NURBS freeform surface

Abstract: A useful description method of an optical surface should have flexible surface description and fitting ability and fast ray-tracing speed, the algorithms for fitting and fast ray tracing of NURBS free-form surface are studied.

Design and fabrication of diffractive optical elements with complex profile by interference

Abstract: A novel method is presented for the design and the fabrication of the Diffractive Optical Elements (DOEs) with arbitrary complex phase profile based on interference. The DOEs are designed to modulate the complex light wave by the analytical formulas, and asymmetric holographic DOE with cubic phase modulation is fabricated by two-step exposure technique on flat plane. Further it is employed for the modulation of the optical intensity on curved surfaces (CS) and apply it to fabricate diffractive optical elements (DOEs) with arbitrary profile and large area on CS. Both a binary pattern and a gray pattern are reconstructed numerically on the lens surfaces with big curvatures in large areas, while a binary and nonperiodic pattern is produced experimentally. The simulations together with the experiment demonstrate the validity of the method. It is believed that micro- or nano- optical elements with smaller feature sizes can be fabricated by the proposed method when an optical microscopy system is used. It will be a very efficient and convenient way to design and fabricate the DOEs with required complex fine structure.

Effect of absence on visual perception and discomfort

Abstract: Prior researches on binocular mismatches of stereoscopic images mostly focus on optical errors (magnification, shift, rotation, distortion) and photometric asymmetries (color, luminance, definition). In this paper, a type of binocular mismatches - effect of absence is investigated to find whether the partial loss of an object in either one of a stereo pair influences characteristics of human fusion and depth perception when certain disparity is provided, in which two situations are taken into account: with overlap and without overlap. Implications for the effect of absence on fusion mechanism and visual comfort are also discussed in this paper. Experimental results prove the conclusion that the effect of absence can cause misperception and contribute to visual discomfort.

Memory usage reduction and intensity modulation for 3D holographic display using non-uniformly sampled computer-generated holograms

Abstract: The real-time holographic display encounters heavy computational load of computer-generated holograms and precisely intensity modulation of 3D images reconstructed by phase-only holograms. In this study, we demonstrate a method for reducing memory usage and modulating the intensity in 3D holographic display. The proposed method can eliminate the redundant information of holograms by employing the non-uniform sampling technique. By combining with the novel look-up table method, 70% reduction in the storage amount can be reached. The gray-scale modulation of 3D images reconstructed by phase-only holograms can be extended either. We perform both numerical simulations and optical experiments to verify the practicability of this method, and the results match well with each other. It is believed that the proposed method can be used in 3D dynamic holographic display and design of the diffractive phase elements.

Fast polygon-based method using 2D Fourier analysis of 3D affine transformation

Abstract: A polygon-based method is proposed for computer-generated holography. One primitive polygon is used to calculate the diffracted wave of each arbitrary polygon. The method does not have Fast Fourier Transform and saves the computation time.

P.52: A Colorful Holographic Display System with Enlarged Viewing Zone Using Multiplex SLMs

Abstract: A full-color holographic display system with enlarged viewing zone by rotational half mirror is presented where the CGHs are divided into several areas to extend the viewing angle based on multiple intensity images with depth map. It can produce the 3D image with correct depth cue, effect of light and shadow.

Assessment of 3D quality of experience with content analysis

Abstract: Stereoscopic display has witnessed rapid progress in recent years, but it still suffers from the bad quality of experience (QoE) problem. Development of more reliable metrics for objective assessment of 3D QoE is challenging. In this paper, we propose a model that combines 2D and 3D features of the analyzed images with SSIM in order to produce more reliable estimation of the perceived subjective quality in terms of mean opinion score (MOS). The model was trained and evaluated on a public stereoscopic image database with associated ground truth MOS. Our results show that the proposed model achieved high correlation with perceived quality and it is promising for objective evaluation of large stereoscopic image dataset after a relatively small training procedure.