The 3-D Hough shape transform

The 3-D Hough shape transform is described which is used for the localization in space of 3-D objects defined in terms of the spatial organization of their features.     

JPEG量化步长估计综述

随着 JPEG(Joint Photographic Experts Group)格式的图片在网络存储和传输中的广泛应用, 基于 JPEG 格式的篡改、 拼接等恶意操作也层出不穷, 利用 JPEG 图像特性的研究受到越来越多的关注。其中, JPEG 图像特性与量化步长息息相关。如果, JPEG 压缩后的图像以位图的形式进行保存, 研究者无法直接获取到量化步长, 从而无法有效地分析 JPEG 图像特性。因此, 对于量化步长的估计在数字图像取证领域越来越受到关注。 本文首先介绍了量化步长估计的研究背景, 并将量化步长估计问题分成两类问题: 单压缩图像的量化步长估计和重压缩图像的首次量化步长估计。其次, 在经典的 JPEG 压缩模型基础上分别了给出了这两类问题的量化步长估计模型, 并对每类问题的各种现有方法进行了详细介绍和梳理。随后, 在相同实验环境下对经典算法进行了实验, 并对经典算法进行了相应的分析与评价。 实验结果表明: 在单压缩图像的量化步长估计任务中, 现有技术相对成熟并且部分算法估计准确率高于 90%; 但是, 在对齐重压缩图像的首次量化步长估计任务中, 现有方法仅能估计低频、中频的量化步长, 并且当首次与第二次的压缩质量因子相近时, 估计准确率较低; 在非对齐重压缩图像的首次量化步长估计任务中, 由于网格偏移会增加估计量化步长的困难, 导致算法在非对齐重压缩上性能较差。最后, 指出了量化步长估计中有待进一步解决的问题和发展趋势。     

三维装配几何约束问题求解研究

讨论了普遍情况下三维几何约束求解的问题.首先,对基本几何元素求解问题进行了研究,在此基础上对两装配体进行装配的几何约束问题进行了研究,提出对三维几何约束复杂耦合问题进行求解的方法,该研究拓展了三维几何约束求解器的通用性.     

基于表面粗糙度的三维模型质量评价研究

数字水印的嵌入会引起三维模型数据的失真,正确评价含水印三维模型的质量可以为三维水印算法的测评提供统一标准。提出了一种新的三维模型质量的评价方法,它首先利用网格模型中二面角为基本度量单位计算出整个原始三维模型的粗糙度,然后在嵌入水印以后用同样的方法计算出含水印三维模型的粗糙度,最后得到嵌入水印前后粗糙度的增量,并将其作为水印嵌入对三维模型造成的失真度的度量。大量实验结果表明,相比传统的质量评价方法,该方法更加适用于三维网格模型。该质量评价方法还可用于评价各种水印攻击对含水印三维模型造成损害的程度。     

Stabilizing the Focal Length Computation for 3-D Reconstruction from Two Uncalibrated Views

In order to reconstruct 3-D shape from two uncalibrated views, one needs to resolve two problems: (i) the computed focal lengths can be imaginary; (ii) the computation fails for fixated images. We present a practical remedy for these by subsampling feature points and fixing the focal length. We first summarize theoretical backgrounds and then do simulations, which reveal a rather surprising fact that when the focal length is actually fixed, not using that knowledge yields better results for non-fixated images. We give an explanation to this seeming paradox and derive a hybrid method switching the computation by judging whether or not the images are fixated. Doing simulations and real image experiments, we demonstrate the effectiveness of our method.     

H.263自适应量化和可变长编码的最优化设计

该文首先概述了低码率图象编码标准H．263,然后着重讨论了自适应量化以及Huffman编码的联合优化设计,其中包括算法设计流程和相应的实现代码,最后给出了有关的实验结果和分析,结果表明该算法能有效地加快编码和解码器的运行速度,同时又能保证一定的图象质量。     

一种新型逻辑函数化简方法——立体化简法

文章在卡诺图化简法的思想基础上设计了一种新型的逻辑函数化简方法——“立体化简法”。用逻辑函数立方体代替卡诺图来表示逻辑函数,在三维立体空间进行逻辑函数的化简,既保持了卡诺图化简法方便、直观、容易掌握的优点,又使得可以方便化简的逻辑函数变量增加至六个;如果采用达到卡诺图化简法五、六变量逻辑函数化简的难易程度的方法,可使化简的逻辑函数变量增加至九个。这种新型的逻辑化简方法使得五、六变量逻辑函数的化简变得非常简单、方便,也使得九变量以内的逻辑函数的化简变得直观、可行。     

基于VRML虚拟现实技术在空间解析几何教学中的应用

基于VRML虚拟现实技术是一项具有广泛应用前景的计算机网络技术,对于三雏显像领域具有特定的重要性,VRML提供了面向对象的方法来描述三雏形体,是对三维形体可视化的极好工具。本文提出了VRML技术在空问解析几何教学中的实现方法以及在教学中的应用。     

刀具CAD中的三维立体造型技术

本文介绍了刀具ＣＡＤ图形处理中的三维立体造型技术。采用几何体素构造法和变差几何法参数化实体造型技术来生成加工中心刀具的绘图模型，并给出了按拓扑关系自动查询图形数据库的方法。     

Recursive 3-D Visual Motion Estimation Using Subspace Constraints

A structure from motion algorithm is described which recovers structure and camera position, modulo a projective ambiguity. Camera calibration is not required, and camera parameters such as focal length can be altered freely during motion. The structure is updated sequentially over an image sequence, in contrast to schemes which employ a batch process. A specialisation of the algorithm to recover structure and camera position modulo an affine transformation is described, together with a method to periodically update the affine coordinate frame to prevent drift over time. We describe the constraint used to obtain this specialisation.Structure is recovered from image corners detected and matched automatically and reliably in real image sequences. Results are shown for reference objects and indoor environments, and accuracy of recovered structure is fully evaluated and compared for a number of reconstruction schemes. A specific application of the work is demonstrated—affine structure is used to compute free space maps enabling navigation through unstructured environments and avoidance of obstacles. The path planning involves only affine constructions.     

Using Multiple-Hypothesis Disparity Maps and Image Velocity for 3-D Motion Estimation

In this paper we explore a multiple hypothesis approach to estimating rigid motion from a moving stereo rig. More precisely, we introduce the use of Gaussian mixtures to model correspondence uncertainties for disparity and image velocity estimation. We show some properties of the disparity space and show how rigid transformations can be represented. An algorithm derived from standard random sampling-based robust estimators, that efficiently estimates rigid transformations from multi-hypothesis disparity maps and velocity fields is given.     

Relation between the medial axis of the foot outline and 3-D foot shape

Posterior flexion angle (PFA) of the medial axis of foot outline is a useful tool for analysing the morphological variation of the human foot. In order to clarify the relation between PFA and the three-dimensional foot shape, the right foot was measured three-dimensionally for 20 male and 39 female subjects. The foot was taken to consist of a series of cross-sections, and morphological characteristics of these sections as well as PFA and the intensity of medial bulge were used to analyse the foot shape. These morphological characteristics were independent of the foot size and correlated with each other. The results of a principal component analysis indicate that the most important variation in the human foot shape is that contrasting a pronated flat foot and a foot of ‘standard’ type. A ‘standard’ type of foot has well-developed plantar arch and straight medial axis, and actually the majority of people do not have this type of foot. The strategies for improving the fit of the shoe in a general population were discussed.     

多功能X射线断层分析装置中三维自动工作台的研制

三维自动工作台是多功能X射线断层分析装置中的关键部件;介绍了多功能X射线断层分析装置的工作原理和三维自动工作台的机械结构;工作台控制系统采用开环控制方式;采用运动控制卡作为步进电机的上位控制单元,运用Visual Basic来编制软件部分,并与运动函数库链接,开发出Windows平台下的运动控制系统;经重庆市计量技术研究所校准检测,三维自动工作台设计合理,控制效果良好.     

3D Photography Using Shadows in Dual-Space Geometry

A simple and inexpensive approach for extracting the three-dimensional shape of objects is presented. It is based on weak structured lighting. It requires very little hardware besides the camera: a light source (a desk-lamp or the sun), a stick and a checkerboard. The object, illuminated by the light source, is placed on a stage composed of a ground plane and a back plane; the camera faces the object. The user moves the stick in front of the light source, casting a moving shadow on the scene. The 3D shape of the object is extracted from the spatial and temporal location of the observed shadow. Experimental results are presented on five different scenes (indoor with a desk lamp and outdoor with the sun) demonstrating that the error in reconstructing the surface is less than 0.5% of the size of the object. A mathematical formalism is proposed that simplifies the notation and keep the algebra compact. A real-time implementation of the system is also presented.     

三维测量中光栅投影条纹边界编码方法的改进

光栅投影法是一种非接触性的快速获取三维物体轮廓的检测方法，此方法一个必要步骤就是对二维图像上的光栅投影进行编码。本文在描述和分析已有的奈纹边界编码的基础上，考虑到工程中的噪声等因素，对原有的边界编码进行了适当的改进，在实际应用中取得了更好的结果。     

Estimation of 3-D translational motion parameters via hadamard transform

A new method based on spatial-temporal Hadamard transform is proposed to estimate the 3-D translational motion parameters. This method has no restriction on the magnitude of displacement. Moreover, for an image of size 2ⁿ × 2ⁿ, only 2n + 1 coefficients need to be computed. Experimental results are demonstrated for this powerful method.     

帧率提升中的三维递归搜索块匹配改进算法

将基于块匹配的运动估计用于帧率提升会产生内插重叠、空洞等问题。对三维递归搜索（3DRS）块匹配运动估计算法进行改进,结合双向运动估计给出更为精确的运动矢量,采用矢量中值滤波器平滑矢量场,并运用中值滤波运动补偿技术进行插帧。实验结果表明,该算法在主客观方面都具有较好的性能,计算复杂度较低,也便于硬件实现。     

综合利用VB与Surfer实现地学三维曲面的动态显示

Surfer软件具有较完美的数据处理和显示功能。文中通过Surfer下编程调用绘图函数,和VB与Surfer混合编程以增强操作交互性这两条途径,在充分利用Surfer强大的绘图功能的基础上,实现了三维曲面的动态显示。     

基于二进制编码结构光测量系统的标定方法

针对基于二进制编码结构光的三维形貌测量系统,利用交比投影不变原理,提出了一种可同时标定摄像机模型参数与投影光平面方程参数的方法。另外,为了克服原系统只能求取部分光平面方程的缺点,利用靶标坐标系与摄像机坐标系之间的约束关系,提出了一种间接标定光平面一般方程的方法。本文阐述了该测量系统的测量原理,提出了标定方案,给出标定结果。实验结果验证了理论分析的正确性和应用的可行性。     

A diffusion wavelet approach for 3-D model matching

This paper proposes a new 3D shape retrieval approach based on diffusion wavelets which generalize wavelet analysis and associated signal processing techniques to functions on manifolds and graphs. Unlike current works on 3D matching, which are based either on the topological information of the model or its scatter point distribution information, this approach uses both information for more effective matching. Diffusion wavelets enable both global and local analyses on graphs, and can capture the topology of a surface with the diffusion map of its mesh representation. As a result, both multi-scale properties of the 3D geometric model and the topology among the meshes can be extracted for use in 3D geometric model retrieval. Tests using 3D benchmarks demonstrate that the approach based on diffusion wavelets is effective and performs better than those by spherical wavelet and spherical harmonics in 3D model matching.