混合漫游系统

提出一种新颖的场景绘制方法,首先对图像进行处理,用交互的方法区分场景的背景和前景;然后分别建立背景和前景的3D几何模型,采用一种分片绘制的策略,进一步提高了绘制质量．通过将动态网格叠加到几何模型中,在静态图像中产生动态纹理,丰富场景内容,从而建立了一种混合场景表示,实现逼真的场景实时漫游．实验证明,该算法具有较好的普适性,可以处理包含灭点或灭线的不同类型照片、绘画和全景图．     

一种视点相关的大规模地形快速实时生成算法

为了解决大规模地形实时漫游过程中,由于不同细节层次模型之间过渡而引起的图像跳变以及图像绘制帧率不高的问题,提出了自底向上的一次性整体构网,网格节点实时更新的建模策略。运用基于块和三角形面片的混合裁剪模式 ,结合简化的高度差投影计算方法,快速选取适合的地形节点 ;然后采用加点、删点、局部更新三种途径对 Delaunay地形三角网进行实时更新。同时在地形漫游过程中实现了对高度差投影限的自适应控制。仿真实验表明,该算法有效地避免了图像跳变现象,与同类算法相比 ,具有较高的图像绘制帧率,特别适合大规模地形的近距离     

基于图像序列的虚拟场景重建和漫游

基于图像的建模和绘制方法与基于传统的几何绘制方法相比有很多优点,但是在场景几何参数未知的情况下,要实现单幅图片和图像序列的漫游,难度很大.TIP（tour into a picture）技术使得在一幅图像中漫游成为可能.为了实现场景几何参数未知情况下的场景漫游,在对TIP技术进行扩展的基础上,提出了一种能够在未知视点路径的图像序列中实现场景漫游的方法.这种算法在相机未定标的情况下,不仅解决了图像序列建模和场景漫游过程中前后图像场景不能平滑过渡的问题,并且扩大了TIP中视线方向变化的动态范围,从而在保证图像质量的情况下,实现了由图像序列到场景的无限制漫游.实际图像序列的实验结果表明,该算法是有效的,具有实际应用价值.     

应用图像蛛网分割的虚拟现实构建

分析了虚拟现实技术中传统变换拼接方法的不足,介绍了蜘蛛网格分割重生成3D虚拟图像的原理与方法,结合构建校园虚拟漫游系统的设计实例,着重介绍了以渲染漫游感受为目的,所提出的若干新概念和采取的若干新措施。     

一种基于TIP技术的场景重建和漫游方法

基于图像的建模和绘制方法与基于传统的几何绘制方法相比有很多优点。但是，在场景几何未知的情况下，要实现单幅图片和图像序列的漫游，难度很大。TIP技术使得在一幅图像中漫游成为可能，但它采用的平面建模方法有很大的局限性。本文在对TIP技术扩展的基础上提出了一种曲面建模的方法。该方法减少了TIP技术的限制，扩展了其适应性。实验结果表明，本文提出的算法是有效的，具有实际应用价值。     

基于场景图的图像缓存绘制加速技术的方法

介绍了一种基于图像缓存技术的绘制加速方法,该方法利用漫游静态场景中视点移动的连续性加速绘制过程。该文介绍了图像缓存算法的基本思想与相关研究,在实现方式中,计算参考四边形与映射四边形相对于视点的角度差,作为衡量缓存纹理是否可用的误差控制标准,文章的最后提出了下一步有待于改进的研究点。     

基于图像的虚拟场景实时漫游

提出一种基于图像的并行绘制算法 ,通过分割图像显示窗口并行绘制 ,实现了三维场景的高分辨率图像的实时绘制 该算法按各节点计算性能分配任务 ,实现了负载平衡 利用三维场景漫游时相邻帧之间的相关性 ,采用RLE(RunLengthEncoded)压缩方法传输图像 ,降低了传输开销 实验结果表明 ,在 4台PC组成的机群上 ,实现了5 12× 5 12大小的图像的实时绘制     

一种基于多边形柱面全景图的虚拟漫游新方法

提出了一种基于图像绘制的多边形柱面全景图的虚拟漫游方法。利用普通 的手持相机在一个多边形区域内沿某一路径拍摄并拼接多幅全景图,通过基于SIFT 的特征 点检测来计算深度,用狭缝图像插值来实现整个区域内的平滑漫游。该方法具有采样简单、 虚拟场景真实感强,支持连续大范围漫游的特点。     

一种新的棋盘格图像角点检测算法

鉴于棋盘格图案在摄像机标定中有着广泛的应用,因此为了对边缘模糊的棋盘格图像进行在线标定,针对目前棋盘格图像角点检测算法的局限性,提出了一种可以自动实现的棋盘格图像角点检测算法,该算法是利用周围图案对称和灰度值对比明显的独特性质,设计了由对称算子S和方差算子V组合而成的角点检测算子--对称方差算子（symmetry and variance）,简称SV算子.该算子不仅构思巧妙、易于实现、计算量小,而且对棋盘格图像的旋转变换和亮度变换具有鲁棒性和抗噪能力强的优点.实验结果表明,该算子对边缘模糊有良好的适应性,适用于摄像机的在线标定.     

基于光线相关性的快速光线投射算法

光线投射算法是一种应用广泛的体绘制技术的基本算法，其存在的主要问题是绘制速度较慢。为了提高光线投射算法的绘制速度，以满足医学图像三维重建的应用需求，在深入研究和比较各种光线投射加速算法的基础上，提出了以接近云算法为核心的、适用于医学图像三维重建的综合性加速算法，并在PC机平台上实现了该算法，在保证图像质量的同时绘制速度提高了一个数量级左右，为医学图像三维重建的实用化提供了有效的手段。     

Tour Into the Picture using a Vanishing Line and its Extension to Panoramic Images

Tour into the picture (TIP) proposed by Horry et al. ¹³ is a method for generating a sequence of walk-through images from a single reference picture (or image). By navigating a 3D scene model constructed from the picture, TIP produces convincing 3D effects. Assuming that the picture has one vanishing point, they proposed the scene modeling scheme called spidery mesh. However, this scheme has to go through major modification when the picture contains multiple vanishing points or does not have any well-defined vanishing point. Moreover, the spidery mesh is hard to generalize for other types of images such as panoramic images. In this paper, we propose a new scheme for TIP which is based on a single vanishing line instead of a vanishing point. Based on projective geometry, our scheme is simple and yet general enough to address the problems faced with the previous method. We also show that our scheme can be naturally extended to a panoramic image.     

基于方向纹理的非结构化道路消失点检测研究

随着车辆智能化的快速推进,道路的自动检测起着越来越重要的作用;但非结构 化道路由于道路标识和边界线不明显,导致检测存在困难。将非结构化道路的消失点作为约束 进行检测,可以大幅度提高检测性能,针对现有的非结构化道路消失点检测方法普遍存在计算 时间长、实时性差等缺点,为提高运算效率,提出了基于局部方向模式(LDP)纹理特征的消失 点检测方法。在计算 LDP 特征基础上,利用 Kirsch 掩模得到像素点的 4 方向响应幅值,并通 过幅值校正减少检测误差;对校正后的响应幅值进行计算得到纹理主方向;使用局部自适应软 投票方法进行投票,选取道路消失点,实现消失点检测。实验结果表明,该方法的速度更快, 且能够准确检测出非结构化道路的消失点。     

Hypercatadioptric line images for 3D orientation and image rectification

In central catadioptric systems 3D lines are projected into conics. In this paper we present a new approach to extract conics in the raw catadioptric image, which correspond to projected straight lines in the scene. Using the internal calibration and two image points we are able to compute analytically these conics which we name hypercatadioptric line images. We obtain the error propagation from the image points to the 3D line projection in function of the calibration parameters. We also perform an exhaustive analysis on the elements that can affect the conic extraction accuracy. Besides that, we exploit the presence of parallel lines in man-made environments to compute the dominant vanishing points (VPs) in the omnidirectional image. In order to obtain the intersection of two of these conics we analyze the self-polar triangle common to this pair. With the information contained in the vanishing points we are able to obtain the 3D orientation of the catadioptric system. This method can be used either in a vertical stabilization system required by autonomous navigation or to rectify images required in applications where the vertical orientation of the catadioptric system is assumed. We use synthetic and real images to test the proposed method. We evaluate the 3D orientation accuracy with a ground truth given by a goniometer and with an inertial measurement unit (IMU). We also test our approach performing vertical and full rectifications in sequences of real images.     

Perspective Geometry Based Single Image Camera Calibration

This paper presents a novel method for 3D camera calibration. Calculation of the focal length and the optical center of the camera are the main objectives of this research work. The proposed technique requires a single image having two vanishing points. A rectangular prism is employed as the calibration target to generate vanishing points. The special arrangement of the calibration object adds more accuracy in finding the intrinsic parameters. Based on the geometry of the perspective distortion of the edges of the prisms from the image, vanishing points are found. There on, fixing up the picture plane followed by fixing up of the station point is carried out based on the relations that are formulated. Experimental results of our method are likened with Zhang’s method. Results are tabulated to show the accuracy of the proposed approach.

Constrained Texture Mapping using Image Warping

We introduce in this paper a new method for smooth foldover-free warping of images. It allows users to specify the constraints in two different ways: positional constraints to constrain the position of points in the image and gradient constraints to constrain the orientation and scaling of some parts of the image. We then show how our method is used for texture mapping with hard constraints. We start with an unconstrained planar embedding of the target mesh calculated with conventional methods. In order to obtain a mapping that satisfies the user-defined constraints, we use our warping method to align the features of the texture image with those of the unconstrained embedding. Compared to previous work, our method generates a smoother texture mapping and offers higher level of control for defining the constraints.     

Using vanishing points for camera calibration and coarse 3D reconstruction from a single image

In this paper, we show how to calibrate a camera and to recover the geometry and the photometry (textures) of objects from a single image. The aim of this work is to make it possible walkthrough and augment reality in a 3D model reconstructed from a single image. The calibration step does not need any calibration target and makes only four assumptions: (1) the single image contains at least two vanishing points, (2) the length (in 3D space) of one line segment (for determining the translation vector) in the image is known, (3) the principle point is the center of the image, and (4) the aspect ratio is fixed by the user. Each vanishing point is determined from a set of parallel lines. These vanishing points help determine a 3D world coordinate system R _o. After having computed the focal length, the rotation matrix and the translation vector are evaluated in turn for describing the rigid motion between R _o and the camera coordinate system R _c. Next, the reconstruction step consists in placing, rotating, scaling, and translating a rectangular 3D box that must fit at best with the potential objects within the scene as seen through the single image. With each face of a rectangular box, a texture that may contain holes due to invisible parts of certain objects is assigned. We show how the textures are extracted and how these holes are located and filled. Our method has been applied to various real images (pictures scanned from books, photographs) and synthetic images.     

An error analysis for surface orientation from vanishing points

Given two parallel lines in a plane, their images formed by central projection onto the viewing plane intersect at a vanishing point, which provides a constraint on the orientation of the plane. Two such independent constraints define a vanishing line and thereby determine the orientation of the plane uniquely. In order to effectively use this information, an estimate of its accuracy must be incorporated. In the approach suggested, line directions and surface normal vectors are represented as points on a Gaussian sphere, and the error bounds are computed as regions on the sphere. Information from multiple vanishing points and surfaces is combined by intersecting the corresponding regions. In addition, constraints based on real-world knowledge can be introduced to improve the accuracy. Some experimental results on natural images re presented to illustrate this method     

Adaptive online transmission of 3-D TexMesh using scale-space and visual perception analysis

Efficient online visualization of three-dimensional (3-D) mesh, mapped with photo realistic texture, is essential for a variety of applications such as museum exhibits and medical images. In these applications synthetic texture or color per vertex loses authenticity and resolution. An image-based view dependent approach requires too much overhead to generate a 360/spl deg/ display for online applications. We propose using a mesh simplification algorithm based on scale-space analysis of the feature point distribution, combined with an associated visual perception analysis of the surface texture, to address the needs of adaptive online transmission of high quality 3-D objects. The premise of the proposed textured mesh (TexMesh)simplification, taking the human visual system into consideration, is the following: given limited bandwidth, texture quality in low feature density surfaces can be reduced, without significantly affecting human perception. The advantage of allocating higher bandwidth, and thus higher quality, to dense feature density surfaces, is to improve the overall visual fidelity. Statistics on feature point distribution and their associated texture fragments are gathered during preprocessing. Online transmission is based on these statistics,which can be retrieved in constant time. Using an initial estimated bandwidth,a scaled mesh is first transmitted. Starting from a default texture quality,we apply an efficient Harmonic Time Compensation Algorithm based on the current bandwidth and a time limit, to adaptively adjust the texture quality of the next fragment to be transmitted. Properties of the algorithm are proved. Experimental results show the usefulness of our approach.