摄象机参数高精度求解方法

提出了一种新的高精度的摄象机参数的求解方法，文章利用透视变换理论建立了摄象机数学模型，模型中考虑了摄象机镜头的径向畸变和切向畸变，首先利用牛顿－高斯非线性搜索方法求争摄象机畸变系数和一个中间矩阵，然后再从中间矩阵中分离出其它模型参数；     

3D测量系统中的高精度摄像机标定算法

本文在分析完整的摄像机镜头畸变模型的基础上,提出了一种新的标定算法.该算法包括三个步骤,首先在不考虑镜头畸变的情况下利用标定块上的中间若干个点,采用线性优化方法求出除畸变系数以外的其他外部参数和主要的内部参数;然后固定上述已求得的参数,利用线性优化方法求解畸变系数;最后对所有内部参数和外部参数进行全局非线性优化.最后对本文的标定算法进行了标定实验,实验结果表明,本文算法的标定精度可以达到0.0367 mm,可以满足高精度三维测量及其他应用的要求.     

带切向畸变的模型可视化摄像机标定

根椐Tsai两步标定方法,在Matlab中首先运用直接线性变换法(DLlr)对摄像机参数进行估计,然后以线性参数为初始值,运用非线性优化方法对摄像机参数进行优化.并对摄像机参数标定过程中的畸变模型进行分析,主要分析了透镜的径向和切向畸变分量.最后根据标定的摄像机参数,实现了摄像机畸变模型可视化.     

不同车型的车辆声音与振动信号特征研究

首先对高速公路现场采集到的两种车型共计74辆车,单辆车行驶时产生的地面振动和车外噪声信号进行AR参数模型分析,然后利用假设检验进行显著性差异检验,并对两种信号发生机理进行了初步讨论,设计了BP神经网络进行分类识别。分析结果表明,不同车型的地面振动和车外噪声信号AR模型参数具有差异性,车辆车外噪声的AR模型参数差异性远大于地面振动的AR模型参数差异性,用来作为车型识别的特征参数是可行的,其单辆车分类的正确率达80%以上。     

薄壁箱梁畸变分析理论的研究

对薄壁箱梁以畸变角和畸变挠度为位移参数的两种畸变理论进行比较分析,证明了两种理论的计算结果是完全一致的。根据箱梁的变位协调关系得出畸变挠度和畸变角的互换性,从而建立了两种理论的控制微分方程的互换方程。采用广义坐标法,明确了畸变中心的定义,确定了畸变位移模式,进而基于能量变分原理,建立了充分考虑剪切变形效应的畸变分析理论,推导了求解的初参数法,研究了剪切变形的影响。结果表明:剪切变形对畸变翘曲应力和横向弯曲应力的影响较小。     

基于两步法的摄像机标定算法

摄像机标定是机器视觉中的一个重要问题.精确的摄像机标定在涉及定量测量的应用中是非常重要的.摄像机标定的目的是得到摄像机的内部参数和外部参数.通过这些参数我们能够将一个点的三维位置与它的图像平面的坐标相匹配.本文提出了一种基于两步法的摄像机标定方法.第一步,使用基于无畸变的相机模型估计标定参数;第二步,在考虑相机畸变的情况下,对第一步中得到的标定参数通过非线性优化进行迭代优化,并求解畸变系数,包括径向畸变系数和切向畸变系数.用单幅图像即可完成标定,标定过程比两步法更为简洁.实验结果表明,这种算法是简单而有效的.     

一种实用的双目显微镜视觉系统标定设计

本文针对显微镜光路复杂对三维物体的放大倍数过大使得采集的图像样本不理想的情况,将双目视觉系统的标定原理与显微系统产生的虚拟双目成像原理结合,提出了一种双目显微小孔成像模型。深入分析了显微摄像机系统的标定及畸变模型,然后,根据张正友的平面模板标定方法和Brown的方法,提出了一种双目标定算法,求解了摄像机内外参数和非线性畸变参数。最后结合Bouguet算法对图形进行校正,通过实验验证了本文所提方法的有效性。     

摄像机径向畸变校正和内参估计的单图标定方法

提出了一种对摄像机的径向畸变进行校正和内参数估计的单图标定方法.拍摄一幅平面标定模板图像,提出若干条直线,拟合在单参数除法畸变模型下的圆弧参数,从而估计出径向畸变.对径向畸变进行校正后,利用标定模板点与经过校正后的图像点之间的对应关系,估计出单应性矩阵.在假定摄像机主点与畸变中心重合的条件下,线性地计算出摄像机焦距初值.以上述线性方法得到的结果为初值,进行非线性优化,最终得到准确的摄像机参数.超广角鱼眼相机和普通数码相机的实验结果表明,本文提出的算法实现简单、适用性广,结果准确,具有较强的实用性.     

同步辐射X射线光刻中热辐射引起掩模畸变的研究

在同步辐射X射线光刻中,由于掩模的初始张应力和掩膜的非均匀受热将使掩模产生热畸变。本文基于BEPC(北京正负电子对撞机)的运行参数和光刻机系统,建立了掩模受热畸变研究的二维动态模型,对同步辐射X射线光刻中热辐射引起的掩模畸变进行了研究。这种研究方法对其他同步辐射光源和等离子脉冲X射线作用下的掩模畸变研究都是普遍适用的。     

三维重构视觉系统的标定

文章基于改进两步法的标定思想,在三维重构中提出了一种新的视觉系统参数标定与镜头畸变修正方法.该方法根据图像中心附近点畸变量较小的性质,利用中心附近点和全场视点对CCD相机和DLP投影仪的内外部参数标定和镜头畸变修正进行分离.在标定过程中,所设计的带标准圆阵列的靶标和伪随机连续方形编码可以实现特征点的自动识别和匹配.实验表明,该方法能快速、方便地对视觉系统参数进行标定和镜头畸变修正.     

A method for correcting radial distortion based on verifying the planarity of specimens

Image distortion is inevitable when an image is captured through a lens. While the digital image measurement technique is getting popular, image distortion problem can result in significant error. A new distortion correction method is proposed in this study. The proposed method is based on the fact that a flat surface should keep flat when it is measured using three-dimensional (3D) digital image measurement technique. The 3D digital image measurement technique adopted in this research is the simplified 3D digital image correlation (DIC) method. Because radial distortion has a more noticeable influence than other types of distortions, this method deals only with radial distortion. A few experiments are carried out in this study to verify the correctness of this method and its accuracy. Both simulated data and actual image data are adopted in these experiments. The results show that this method can achieve a good accuracy. The standard deviations caused by random errors are about the same order as the random errors. It also shows that this method is suitable for both large and small distortion conditions.     

摄影测量中相机倾斜引起的射影失真研究

根据成像原理,建立了理想光学系统成像的数学模型。通过分析该模型中物与像的对应关系,得出了射影失真产生的根源是光学系统放大率的不恒定,并与相机的外参数:倾角及视场的大小有着非线性的变化关系。提出了正射影失真与负射影失真的概念,对其进行了详尽的理论分析,并给出了数学模型及分布规律。依据上述结论,分析了二维射影对应与仿射对应在摄影测量应用中的实质区别,并利用物像平面间的射影对应关系,使试验中的测量精度达到了测试的要求。     

Efficient depth map compression for view rendering in 3D video

Abstract

A depth map represents three-dimensional (3D) scene information, which is used to synthesise virtual views in 3D video coding. Since the quality of synthesised virtual view highly depends on the quality of depth map, efficient depth coding is crucial for the 3D video system. However, depth map is not directly used for display but to generate virtual views. Compressing depth map using existing video coding techniques yields unacceptable distortions in rendered virtual view. Thus, the depth map needs to be compressed in a way that can minimise distortions in the rendered views. To solve this problem, we propose an efficient depth map compression method for view rendering based on view rendering distortion other than depth map distortion itself. Firstly, we derive relationship between distortion in coded depth map and the rendered view. Then, a region-based video characteristic distortion model is proposed to precisely estimate distortion in view synthesis. Finally, a multilateral filtering is applied as an in-loop filter to reduce rendering artefacts. Experimental results show that the proposed method achieves 2 dB coding gain in terms of PSNR and subjective quality improvement of synthesised views.     

一种新的非线性失真评价方法

提出了一种新的非线性失真客观评价方法。评价信号选用多频声,原始信号和失真后的信号通过听觉模型处理,得到感知倒谱距离,在此基础上将感知倒谱距离计权后得到所需要的客观评价参量。主观验证实验表明,当选取合适的评价节目源时,主客观评价结果的相关度均可达到0.84以上。     

Blind removal of lens distortion

Virtually all imaging devices introduce some amount of geometric lens distortion. A technique is presented for blindly removing these distortions in the absence of any calibration information or explicit knowledge of the imaging device. The basic approach exploits the fact that lens distortion introduces specific higher-order correlations in the frequency domain. These correlations can be detected by using tools from polyspectral analysis. The amount of distortion is then estimated by minimizing these correlations.     

T700轴向增强经编织物复合材料力学性能的模拟分析与试验研究

应用一种新型界面元模型研究了复合材料层间剪切损伤。通过引入双线性损伤准则和损伤演化,预报复合材料层间裂纹扩展。轴向增强经编织物复合材料由针织纱线引起的纤维变形(KYD)产生了富树脂区域,基于细观力学理论提出了一种新的研究轴向增强经编织物单胞模型受单向拉伸和剪切时KYD区周围应力分布的方法,得出了单胞在受载时首先在这一区域产生裂纹。对单轴向T700经编织物复合材料进行了三点弯曲性能和层间剪切性能试验测试,分析了经编织物复合材料的力学特性。分别模拟了弯曲性能和层间剪切性能试验,得出了最大预报载荷值与试验值误差小于10%,并基于有限元模型研究了复合材料面内损伤和层间裂纹扩展损伤机制。     

Analysis and correction of ultrasonic wavefront distortion based on a multilayer phase-screen model

A model is introduced that incorporates the cumulative wavefront distortion effects caused by spatial heterogeneities along the path of propagation, and a corresponding model-based wavefront distortion-correction method is presented. In the proposed model, a distributed heterogeneous medium is lumped into a series of parallel phase screens. The distortion effects can be compensated-without a priori knowledge of the distorting structure-by backpropagation of received wavefronts through hypothetical multiple phase screens located between the imaging system and targets, while each pointwise time shift is adjusted iteratively to maximize a specified image quality factor at the final layer. Theoretical analyses indicate that the mean speckle brightness decreases monotonically with the root-mean-square value of distributed phase distortions; therefore, the speckle brightness can be used as an image quality factor. Experimental one-dimensional (1-D) array data with simulated distortion effects based on a real 2-D abdominal-tissue map were used to evaluate the performance of the proposed method and existing aberration-correction techniques. The simulated characteristics of wavefront distortion and relative performance of existing correction techniques were similar to reports based on abdominal-wall data and breast data. This investigation shows that the proposed method provides better compensation for wavefront distortion.     

Nonrandom quantization errors in timebases

Timebase distortion causes nonlinear distortion of waveforms measured by sampling instruments. When such instruments are used to measure the RMS amplitude of the sampled waveforms, such distortions result in errors in the measured RMS values. This paper looks at the nature of the errors that result from nonrandom quantization errors in an instrument timebase circuit. Simulations and measurements on a sampling voltmeter show that the errors in measured RMS amplitude have a nonnormal probability distribution, such that the probability of large errors is much greater than would be expected from the usual quantization noise model. A novel timebase compensation method is proposed which makes the measured RMS errors normally distributed and reduces their standard deviation by a factor of 25. This compensation method was applied to a sampling voltmeter and the improved accuracy was realized     

The Method Based on Original DBFs for Fast Estimation of Waveform Distortions in Ship Systems—Case Study

This paper deals with the problem of fast recognition of harmonic distortions by means of a wavelet transform. A method of fast detection of a frequency band affected by the high-frequency content and time of its occurrence is described. It is based on the auxiliary waveform distortion band factors (DBFs) calculated on the basis of wavelet coefficients. The merits of the presented method, as well as its limitations, are described on the basis of real voltages registered in ships' electrical power systems. This method is a part of the method based on the complementary application of Fourier and wavelet transforms, which was described in the previous papers of the author. However, this paper describes new research results and an expanded analysis exclusively focused on the aforementioned DBFs.