Image‐based detail reconstruction of non‐Lambertian surfaces

This paper presents a novel optimization framework for estimating the static or dynamic surfaces with details. The proposed method uses dense depths from a structured‐light system or sparse ones from motion capture as the initial positions, and exploits non‐Lambertian reflectance models to approximate surface reflectance. Multi‐stage shape‐from‐shading (SFS) is then applied to optimize both shape geometry and reflectance properties. Because this method uses non‐Lambertian properties, it can compensate for triangulation reconstruction errors caused by view‐dependent reflections. This approach can also estimate detailed undulations on textureless regions, and employs spatial‐temporal constraints for reliably tracking time‐varying surfaces. Experiment results demonstrate that accurate and detailed 3D surfaces can be reconstructed from images acquired by off‐the‐shelf devices. Copyright © 2010 John Wiley & Sons, Ltd.     

3D interactive system based on vision computing of direct‐flective cameras

A bare‐finger 3D interactive technology for portable devices was developed. Using directive‐flective cameras to reform the field of viewing, a blind working range close to the camera is eliminated. Moreover, the algorithm of vision computing, different from skin color detection, is presented to determine the positions of fingertips. The interactive range is workable from 1.5 to 50 cm above the entire surface of the display. The mean position error of less than 1 cm is achieved. This accuracy realizes a camera‐based 3D interactive system allowing for near‐distance functionality. Therefore, floating 3D images can be touched and interacted with, potentially creating more application and intuitive user‐machine interface.     

基于网格变形的从图像重建三维人脸

从图像重建高质量三维人脸一直是计算机视觉和图形学的一个重要研究问题.不同于传统的基于立体匹配的窄基线多视几何和数据驱动的人脸形变方法,提出一种结合网格变形技术和立体视觉原理的、从图像重建高质量三维人脸模型方法.给定从不同视角拍摄的几幅人脸图像,基于健壮图像特征获得可靠的相机外部参数和稀疏三维点;在此基础上,提出一种结合几何细节保持和图像一致性约束的三维人脸变形算法重建三维人脸,通过对人脸模板的网格变形,使得变形人脸在多幅图像中的可见投影具有一致性的图像颜色强度.基于模板的人脸变形可以有效地解决三维模型成像中的遮挡问题,采用健壮估计法消除噪声、离群点和光照对目标函数收敛性的影响,对目标函数的多次非线性优化求解进一步改进了人脸重建的质量.采用合成人脸图像和真实人脸图像重建三维人脸的实验结果表明,文中算法可以从几幅宽基线图像重建高质量的三维人脸模型.     

基于图像的树类物体的三维重建

树类物体的三维重建一直是人们很感兴趣的一个研究内容。该文利用基于图像的建模技术，实现了一个从双视点图像重建树木三维模型的系统，提出了一个自动获取树木二维主干骨架的方案，实现了二维骨架点的对应关系求解，三维骨架点的重建、简化及树表面网格的生成。实验结果表明该文提出的方法确实可行、有效。     

基于二次Bezier曲面的图像雕刻型面建模

针对纹理清晰且结构较简单的图像,依据其灰色或彩色像素信息,利用二次Bezier曲面直接构建雕刻型面模型。该方法通过对图像进行分割,分析和计算图像子块的像素值及位置参数,作为构建模型曲面片的特征参数,并对曲面片采用一种有限光滑拼接方法实现建模。构建的雕刻型面模型能够表述图像中原物体的基本结构特征,并能满足数字化雕刻加工的需要。算法复杂度较低,实用性强是该建模方法的特点。     

Circular camera array system for 3‐D displays based on the reconstruction of parallax rays

Abstract— A circular camera system employing an image‐based rendering technique that captures light‐ray data needed for reconstructing three‐dimensional (3‐D) images by using reconstruction of parallax rays from multiple images captured from multiple viewpoints around a real object in order to display a 3‐D image of a real object that can be observed from multiple surrounding viewing points on a 3‐D display is proposed. An interpolation algorithm that is effective in reducing the number of component cameras in the system is also proposed. The interpolation and experimental results which were performed on our previously proposed 3‐D display system based on the reconstruction of parallax rays will be described. When the radius of the proposed circular camera array was 1100 mm, the central angle of the camera array was 40°, and the radius of a real 3‐D object was between 60 and 100 mm, the proposed camera system, consisting of 14 cameras, could obtain sufficient 3‐D light‐ray data to reconstruct 3‐D images on the 3‐D display.     

实时交互的带浮雕纹理的三维模型构建方法

为了快速生成带浮雕纹理的三维模型,提出一种实时交互的浮雕纹理模型构建方法。方法分两步：第一步,将生成浮雕的源模型或图像转换为初始深度图,并进一步转换为梯度图,再通过梯度域的压缩、过滤,求解线性方程重建出整体连续的浮雕深度图;第二步,借助基于网格求交的浮雕纹理映射算法将浮雕深度图贴在目标模型表面,并通过移动、旋转、缩放等操作实时在目标模型三维空间上修改浮雕效果,最终重建目标模型网格,生成浮雕纹理模型。实验表明,所提方法可快速实现在一个目标模型上生成凹浮雕、凸浮雕、多浮雕等效果,所得模型无需经过其他处理,可直接应用于3D打印,打印效果较好。     

一种为三维物体表面添加纹理的精确方法*

针对真实物体进行三维数字化重建的工程中,物体的空间位置及色彩等特征的数据采集始终是一项困难的,同时却又是十分重要的工作,设计的三维光学数字成像系统可以同时采集物体在同一个方向的深度图像和与它精确对应的纹理图像,在深度图像合成的同时进行纹理图像的融合.在进行多视角的纹理图像融合时,对权函数的设定提出了新的准则,使融合后的纹理图像更加逼真,可以产生高真实感的物体三维数字化模型.     

Interactive Image‐Guided Modeling of Extruded Shapes

A recent trend in interactive modeling of 3D shapes from a single image is designing minimal interfaces, and accompanying algorithms, for modeling a specific class of objects. Expanding upon the range of shapes that existing minimal interfaces can model, we present an interactive image‐guided tool for modeling shapes made up of extruded parts. An extruded part is represented by extruding a closed planar curve, called base, in the direction orthogonal to the base. To model each extruded part, the user only needs to sketch the projected base shape in the image. The main technical contribution is a novel optimization‐based approach for recovering the 3D normal of the base of an extruded object by exploring both geometric regularity of the sketched curve and image contents. We developed a convenient interface for modeling multi‐part shapes and a method for optimizing the relative placement of the parts. Our tool is validated using synthetic data and tested on real‐world images.     

Hybrid image‐based collision detection in Java 3D

Collision detection is highly important in computer graphics and virtual reality. Most collision detection methods are object‐based, relying on testing the geometrical interference of objects, and their performance therefore depends on the geometrical complexity of the objects. Recently, image‐based methods have gained increasing acceptance for their simplicity in implementation, robustness with respect to the object geometry, and the potential to distribute the computational burden onto graphics hardware. However, all existing image‐based methods require direct calls to OpenGL, but so far there is no direct way to access OpenGL through the Java 3D API. Although Java 3D provides its own built‐in collision detection classes, they are either incorrect or inefficient. In this paper, we present a hybrid image‐based collision detection method in Java 3D, which incorporates the Java 3D built‐in collision detection and the image‐based collision detection in our specially devised scene graph. In addition, we take advantage of the fact that the 3D position of successive offscreen views (i.e. virtual views perceived by the probing object) does not change significantly and thereby reduce the occurrences of offscreen rendering, so that the collision detection becomes even faster (up to 50% in our case). Experimental results prove the correctness and efficiency of our method. Copyright © 2006 John Wiley & Sons, Ltd.     

A computational model of bounded developable surfaces with application to image‐based three‐dimensional reconstruction

Developable surfaces have been extensively studied in computer graphics because they are involved in a large body of applications. This type of surfaces has also been used in computer vision and document processing in the context of three‐dimensional (3D) reconstruction for book digitization and augmented reality. Indeed, the shape of a smoothly deformed piece of paper can be very well modeled by a developable surface. Most of the existing developable surface parameterizations do not handle boundaries or are driven by overly large parameter sets. These two characteristics become issues in the context of developable surface reconstruction from real observations. Our main contribution is a generative model of bounded developable surfaces that solves these two issues. Our model is governed by intuitive parameters whose number depends on the actual deformation and including the “flat shape boundary”. A vast majority of the existing image‐based paper 3D reconstruction methods either require a tightly controlled environment or restricts the set of possible deformations. We propose an algorithm for reconstructing our model's parameters from a general smooth 3D surface interpolating a sparse cloud of 3D points. The latter is assumed to be reconstructed from images of a static piece of paper or any other developable surface. Our 3D reconstruction method is well adapted to the use of keypoint matches over multiple images. In this context, the initial 3D point cloud is reconstructed by structure‐from‐motion for which mature and reliable algorithms now exist and the thin‐plate spline is used as a general smooth surface model. After initialization, our model's parameters are refined with model‐based bundle adjustment. We experimentally validated our model and 3D reconstruction algorithm for shape capture and augmented reality on seven real datasets. The first six datasets consist of multiple images or videos and a sparse set of 3D points obtained by structure‐from‐motion. The last dataset is a dense 3D point cloud acquired by structured light. Our implementation has been made publicly available on the authors' web home pages. Copyright © 2012 John Wiley & Sons, Ltd.     

A 2D–3D integrated tabletop environment for multi‐user collaboration

This paper proposes a novel tabletop display system for natural communication and flexible information sharing. The proposed system is specifically designed to integrate two‐dimensional (2D) and three‐dimensional (3D) user interfaces by using a multi‐user stereoscopic display, IllusionHole. The proposed system takes awareness into consideration and provides both 2D and 3D information and user interfaces. On the display, a number of standard Windows desktop environments are provided as personal workspaces, as well as a shared workspace with a dedicated graphical user interface. In the personal workspaces, users can simultaneously access existing applications and data, and exchange information between personal and shared workspaces. In this way, the proposed system can seamlessly integrate personal, shared, 2D, and 3D workspaces with conventional user interfaces and effectively support communication and information sharing. To demonstrate the capabilities of the proposed display system, a modeling application was implemented. A preliminary experiment confirmed the effectiveness of this system. Copyright © 2006 John Wiley & Sons, Ltd.     

Computer display control and interaction using eye‐gaze

Innovative systems for user‐computer interaction based on the user's eye‐gaze behavior have important implications for various applications. Examples include user navigation in large images, typical of astronomy or medicine, and user selection and viewing of multiple video streams. Typically, a web environment is used for these applications. System latency must be negligible, while system obtrusiveness must be small. This paper describes the implementation and initial experimentation on such an innovative system.     

基于双目立体视觉的三维舌重建

舌像蕴含着大量的人体生理病理信息,是中医四诊的重要内容之一。当前中医客观化舌诊研究基于二维舌图像,从中可得到颜色、形态等多种信息,但其不能反映点刺、裂痕等细节信息。为了得到全面的生理信息,本文提出一种基于双目立体视觉的三维舌表面重建方法,适用于具有动态特性的真实舌,达到了0.1342 mm的分辨率。此方法突破了现有以医学诊断为目的的舌表面重建方法动态特性与分辨率不兼得的瓶颈。全面的生理信息为疾病的正确诊断和早期发现提供了保障,同时可解决二维舌像由于深度信息缺失而造成的诸多技术难题,如舌体分割困难等。     

Parametric modeling of microwave filter using combined MLS‐SVR and pole‐residue‐based transfer functions

In this article, an advanced technique is developed to combine multi‐output least‐squares support vector regression (MLS‐SVR) and pole‐residue‐based transfer function models for microwave filter parametric modeling. MLS‐SVR is trained to learn the relationship between the length of tuning screws and the pole/residues of the transfer function, where MLS‐SVR is an effective method to cope with the multi‐output case unlike the traditional approach. Traditional approach treats the different outputs separately in the multi‐output case and it cannot model the relation between different outputs. Another important element for modeling is feature parameters. Extracted feature parameters have an important influence on the accuracy of modeling. For the purpose of establishing a more accurate model, the complex system poles and residues from Y‐parameters are chosen as the outputs of modeling, which are obtained by vector fitting (VF). Then we give a solution to obtaining pole/residues extracted by VF when the filter is in high detuned. After the proposed modeling process, trained model can be used to provide an accurate and fast prediction of the behavior of microwave filter with the length of tuning screws as variables, and model the electromagnetic simulation (or actual) microwave filter tuning. The methodology is applied to a narrow band coaxial‐resonator filter modeling, and more accurate results are achieved compared with the other methods. An example is presented to illustrate the efficiency of the proposed method.     

Controllable Image‐Based Transfer of Flow Phenomena

Modelling flow phenomena and their related weathering effects is often cumbersome due their dependence on the environment, materials and geometric properties of objects in the scene. Example‐based modelling provides many advantages for reproducing real textures, but little effort has been devoted to reproducing and transferring complex phenomena. In order to produce realistic flow effects, it is possible to take advantage of the widespread availability of flow images on the Internet, which can be used to gather key information about the flow. In this paper, we present a technique that allows the transfer of flow phenomena between photographs, adapting the flow to the target image and giving the user flexibility and control through specifically tailored parameters. This is done through two types of control curves: a fitted theoretical curve to control the mass of deposited material, and an extended colour map for properly adapting to the target appearance. In addition, our method filters and warps the input flow in order to account for the geometric details of the target surface. This leads to a fast and intuitive approach to easily transfer phenomena between images, providing a set of simple and intuitive parameters to control the process.     

Large‐signal modeling methodology for GaN HEMTs for RF switching‐mode power amplifiers design

A large‐signal model for GaN HEMT transistor suitable for designing radio frequency power amplifiers (PAs) is presented along with its parameters extraction procedure. This model is relatively easy to construct and implement in CAD software since it requires only DC and S‐parameter measurements. The modeling procedure was applied to a 4‐W packaged GaN‐on‐Si HEMT, and the developed model is validated by comparing its small‐ and large‐signal simulation to measured data. The model has been employed for designing a switching‐mode inverse class‐F PA. Very good agreement between the amplifier simulation and measurement shows the validity of the model. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Computer‐vision determination of 3‐D geometric parameters of LDL particles via cryogenic transmission electron microscopy

Abstract— Previous research has shown that the size of the LDL macromolecules can have an effect on cardiovascular health and that LDL macromolecules may be non‐spherical in shape. Some of these studies, however, used methods that are not conducive to automatic determination of the 3‐D parameters of the particles. In particular, the prior methods used for determination of geometric‐parameter determination were either centrifugal separations or manual determination of parameters from cryogenic transmission electron micrographs. An application of computer‐vision techniques to automatically determine the 3‐D parameters from cryogenic transmission electron microscopy (CTEM) images will be described. Correlation of computer‐generated geometric models to the orthonormal projection CTEM imagery were investigated to determine the applicability of finding the pertinent geometric parameters of the expected discoid shape of the LDL particles. The processing showed that the discoid shape can be verified using small‐angle rotations that are more amenable to the limitations of CTEM imaging.     

Efficient Image‐Based Proximity Queries with Object‐Space Precision

We present an efficient algorithm for object‐space proximity queries between multiple deformable triangular meshes. Our approach uses the rasterization capabilities of the GPU to produce an image‐space representation of the vertices. Using this image‐space representation, inter‐object vertex‐triangle distances and closest points lying under a user‐defined threshold are computed in parallel by conservative rasterization of bounding primitives and sorted using atomic operations. We additionally introduce a similar technique to detect penetrating vertices. We show how mechanisms of modern GPUs such as mipmapping, Early‐Z and Early‐Stencil culling can optimize the performance of our method. Our algorithm is able to compute dense proximity information for complex scenes made of more than a hundred thousand triangles in real time, outperforming a CPU implementation based on bounding volume hierarchies by more than an order of magnitude.     

Reconstruction of dynamic 3D scene based on visual hull and view morphing

In this paper, we propose a new method that processes multiple synchronized video sequences and generates 3D rendering of dynamic objects in the video. It exploits an efficient image‐based reconstruction scheme that constructs and shades 3D models of objects from silhouette images by combining image‐based visual hull and view morphing. The proposed hybrid method improves the speed and the quality of the previous visual hull sampling methods. We designed and implemented a system based on this method which is relatively low cost and does not require any special hardware or specific environment. Copyright © 2003 John Wiley & Sons, Ltd.