基于三幅图像的曲面造型及纹理提取

利用标准的参数曲面来表示真实的三维曲面物体，并将物体正面、侧面及背面拍摄图像的侧影轮廓线作为约束，通过最小化线性约束下的二次目标函数实现曲面造型。将曲面重新投影到物体的正面、背面及侧面图像上，利用基于重心坐标的加权纹理提取方法提取纹理图像。利用真实图像实现了逼真的曲面造型，验证了该方法的可行性和正确性。     

基于双视角的可见外壳三维重建研究

针对双目视觉重建方法在三维重建过程中步骤繁琐与重建效果不理想的问题,文中提出了一种基于双视角下可见外壳的三维重建方法。该方法主要借助平面镜成像原理,在不同视角拍摄包含物体与其成像的两幅图像,并根据成像原理确定物体之间的位置关系。通过相机与周围物体的运动关系求得相机参数,实现相机自标定。然后根据阈值分割及区域生长算法处理边缘信息得到目标轮廓,通过可见外壳方法计算侧影轮廓线,连接轮廓线形成重建模型。该方法通过自适应可见外壳种子体素生长在不了解物体先验知识的情况下完成重建。文中对比文献"基于图像轮廓的三维重建方法"中的单视角重建物体方法,提出了双视角重建物体模型方法。实验结果表明,双视角重建方法简单实用,生成的三维模型准确真实。     

基于轮廓和多相关局部顶点优化的三维重构法

如何快速准确的获取真实物体的三维模型受到了人们的普遍关注,针对这个问题,给出了一种能够利用一系列已标定图像中的侧影轮廓线信息重构模型的建模方法.方法中摄像机以物体为中心做圆周运动,间隔固定的角度进行拍照.对获取的图像进行处理,提取其侧影轮廓线.使用Marching Cubes算法重构物体的表面,利用物体在多幅图像中的纹理一致性原理,进行多相关局部顶点优化,并应用到了模型顶点的优化过程之中.最终可以得到品质较好的三维网格表示的物体的三维模型.     

基于图像轮廓的三维重建方法

根据平面镜成像原理,提出了一种基于单幅图像的侧影轮廓线可见外壳重建方法。利用成角度平面镜装置模拟实现多相机同时拍摄,对图像中各轮廓线之间极线几何关系的分析得到对应的相机参数,实现目标物体的三维重建。实验结果表明,该方法简单有效,不需要通过实验室条件下的特殊仪器进行标定即可实现目标物体的三维重建,具有一定的实用价值。     

单视图对称曲面建模及纹理提取

给出了镜面对称物体的水平图像等价于从另外一个位置拍摄图像的完整证明。利用物体中平行结构实现相机标定。在原始图像和水平翻转图像上匹配特征点,通过传统的基于运动的重建技术恢复特征点的位置。把特征点的位置、共面、共线、透视投影等作为约束,通过最小化线性约束下的二次目标函数实现曲面重建。最后采用基于重心坐标的加权纹理提取方法提取纹理图像。利用真实的图像验证了该方法的可行性。     

基于侧影轮廓的图像三维重建方法

针对自标定单幅图像的三维重建问题,提出一种基于侧影轮廓的图像三维重建方法。使用成角度平面镜装置拍摄目标物体,对所得图像进行边缘跟踪,得到闭合的轮廓曲线,利用满足平面镜成像原理的2对侧影轮廓计算灭点,根据灭点间的约束关系计算相机参数,在此基础上重建得到物体的三维模型。实验结果表明,该方法能快速重建逼真的三维模型。     

基于多幅实拍照片为真实景物模型添加纹理

利用实拍照片为基于真实景物创建的几何模型添加纹理的方法正在受到广泛的关注,实拍照片与几何模型的配准是这项技术的关键.以往方法采用3D-2D特征点匹配或侧影轮廓线匹配的方法进行配准,因此对空间物体的表面特征或轮廓线形状有特殊的要求.提出了一种新的配准方法来解决这一问题,由于采用了基于图像重建的采样点模型与已知几何模型在空间中匹配的方法实现配准,因而充分利用了物体几何形状本身的拓扑和曲率等信息,并可以一次性地实现所有图像与空间物体的配准.实验结果表明,该方法可以解决一部分用以往的方法尚无法处理的实际问题,且在重建空间采样点分布较为合理的情形下,纹理映射效果非常理想.     

基于等值面优化重建医学图像的改进算法

医学图像可视化技术利用二维医学图像序列重建出三维模型,为医生提供了直观、全面、准确的病灶和正常组织信息.传统的方法直接采用由序列轮廓线生成的三角片来拟合曲面,重建的速度与效果均有限.为了提高医学三维图像的重建速度和效果,在对用于构造等值面的MCfMarching cubes)算法进行分析的基础上,提出一种三点线性插值法代替相邻多边形顶点的位置,并对等值面法向矢量场进行平滑,实现了目标图像的三维重建.     

隐式曲面上两相图像分割的变分水平集方法

在平面图像分割的Chan-Vese模型基础上,提出隐式曲面上两相图像分割模型。用静态水平集函数的零水平集表达图像所在的闭合曲面,用另一动态水平集函数的零水平集与静态水平集函数零水平集的交线表达静态曲面上图像分割的动态轮廓线。所研究模型的能量泛函的数据项即为曲面上两分割区域的图像强度与对应区域平均图像强度的差的平方,其轮廓线长度项为两水平集函数的零水平集交线的长度。为避免动态水平集函数的重新初始化,在能量泛函中引入水平集函数为符号距离函数的约束惩罚项。通过变分方法得到图像分割空间轮廓线演化的梯度降方程。通过显式差分格式对演化方程进行离散。实验结果表明,该模型能有效实现复杂封闭曲面上图像的两相分割。     

一种由轮廓线重建物体表面的方法

针对基于轮廓线拼接重建物体表面所出现的轮廓对应和分叉问题,提出了一种通过体数据转换由轮廓线实现重建物体表面的方法。在分析体数据构造中出现逼近精度问题的前提下,通过提高轮廓线上点的密度,生成精确度较高的体数据。该方法通过对相邻层轮廓线区域的集合运算,只对处于集合运算解中的像素点进行距离函数值的计算。采用MC（Marching Cubes）算法生成等值面,完成物体的表面重建。实验结果表明,该方法能顺利解决基于轮廓线拼接重建物体表面中出现的轮廓对应问题和分叉问题,既提高重建表面精确度,又加快整个表面的重建速度,是一种可行的方法。     

Shape recovery from turntable sequence using rim reconstruction

This paper makes use of both feature points and silhouettes to deliver fast 3D shape recovery. The algorithm exploits object silhouettes in two views to establish a 3D rim curve, which is defined with respect to the two frontier points arising from two views. The images of this 3D rim curve in the two views are matched using cross-correlation technique. A 3D planar rim curve is then reconstructed using point-based reconstruction method. A set of 3D rim curves enclosing the object can be obtained from an image sequence captured under circular motion. Silhouettes are further utilized to check for mismatched rim points. The proposed method solves the problem of reconstruction of concave object surface, which is usually left unresolved in general silhouette-based reconstruction methods. In addition, the property of the reconstructed 3D rim curves allows fast surface extraction. Experimental results with real data are presented.     

A semi-supervised approach to space carving

In this paper, we present a semi-supervised approach to space carving by casting the recovery of volumetric data from multiple views into an evidence combining setting. The method presented here is statistical in nature and employs, as a starting point, a manually obtained contour. By making use of this user-provided information, we obtain probabilistic silhouettes of all successive images. These silhouettes provide a prior distribution that is then used to compute the probability of a voxel being carved. This evidence combining setting allows us to make use of background pixel information. As a result, our method combines the advantages of shape-from-silhouette techniques and statistical space carving approaches. For the carving process, we propose a new voxelated space. The proposed space is a projective one that provides a colour mapping for the object voxels which is consistent in terms of pixel coverage with their projection onto the image planes for the imagery under consideration. We provide quantitative results and illustrate the utility of the method on real-world imagery.     

3D reconstruction using silhouettes from unordered viewpoints

In this paper, we present a novel approach for reconstructing an object surface from its silhouettes. The proposed approach directly estimates the differential structure of the surface, and results in a higher accuracy than existing volumetric approaches for object reconstruction. Compared with other existing differential approaches, our approach produces relatively complete 3D models similar to volumetric approaches, with the topology conforming to what is observed from the silhouettes. In addition, the method neither assumes nor depends on the spatial order of viewpoints. Experimental results on both synthetic and real world data are presented, and comparison is made with other existing approaches to demonstrate the superiority of the proposed approach.     

微操作系统中微观对象三维立体形状重构研究

研究基于体视显微镜的微操作系统中微观对象的三维立体形状重构问题．体视显微镜的两子光路具有对称性和微小的差异性，差异性是影响微观对象重构准确性的重要因素．文中使用不同的参数序列描述两子光路的对称性和差异性，建立从二维图像空间向三维物空间映射的视觉模型，使用弱视差描述微观立体图像的相关性．通过实验分析视觉模型在三维物空间X，Y，Z三个方向上的重构精度，平均值分别为0．74％，1．98％和6．66％，重构了平面样品和曲面样品的三维立体形状．     

The visual hull concept for silhouette-based image understanding

Many algorithms for both identifying and reconstructing a 3-D object are based on the 2-D silhouettes of the object. In general, identifying a nonconvex object using a silhouette-based approach implies neglecting some features of its surface as identification clues. The same features cannot be reconstructed by volume intersection techniques using multiple silhouettes of the object. This paper addresses the problem of finding which parts of a nonconvex object are relevant for silhouette-based image understanding. For this purpose, the geometric concept of visual hull of a 3-D object is introduced. This is the closest approximation of object S that can be obtained with the volume intersection approach; it is the maximal object silhouette-equivalent to S, i.e., which can be substituted for S without affecting any silhouette. Only the parts of the surface of S that also lie on the surface of the visual hull can be reconstructed or identified using silhouette-based algorithms. The visual hull depends not only on the object but also on the region allowed to the viewpoint. Two main viewing regions result in the external and internal visual hull. In the former case the viewing region is related to the convex hull of S, in the latter it is bounded by S. The internal visual hull also admits an interpretation not related to silhouettes. Algorithms for computing visual hulls are presented and their complexity analyzed. In general, the visual hull of a 3-D planar face object turns out to be bounded by planar and curved patches     

Rendering Silhouettes with Virtual Lights

We present a new method for obtaining non-photorealistic images. These images have two main visual components: silhouettes and non-realistic colouring. Silhouettes are lines that define the form of an object. They are used in classical animation and illustration as the main expressive components. In these applications, if it is necessary, colouring can be added once the drawings are made. For instance, generally, in illustration, colouring is flat and does not transmit volume information whilst silhouettes do it in an economical way. The proposed method is based on the Virtual Lights model, which allows us to use external components, the virtual lights, to define silhouettes. In this way, the designer is free to control where, when and how the silhouettes must appear. The method can be used with B-rep geometric models.     

从二维系列摄影图片提取剪影重构三维实体的光线跟踪算法

给出了利用二维系列摄影图片提取剪影重构三维实体的一种新算法,即围绕一个三维实体从多个角度拍摄照片,然后从照片中提取出实体的边界,通过基于光线跟踪的、对二维影像的合成得到原物体近似表面的三维点坐标,与传统的基于体像素的算法相比,该算法节省存储空间,近似精度与三维分辨率无直接关系,而且速度有所提高,特别当实体体积较大时,效果明显。     

任意摆放的二次曲面体的三维重建

本文采用特征点匹配的方法,先由二维视力获取三维空间的点和曲线,然后经过一系列线性运算得出三维曲面。本算法可对任意二次曲面进行三维重建,不仅对曲面的空间摆放沿有限制,而且对曲面自身的对称性也无要求。因此,可将重建对象扩展为圆柱、椭圆柱、球、椭球、双曲面、抛物面等。本文给出的算例表明了算法的有效性。