Bubble behavior characteristics based on virtual binocular stereo vision

The three-dimensional (3D) behavior characteristics of bubble rising in gas-liquid two-phase flow are of great importance to study bubbly flow mechanism and guide engineering practice. Based on the dual-perspective imaging of virtual binocular stereo vision, the 3D behavior characteristics of bubbles in gas-liquid two-phase flow are studied in detail, which effectively increases the projection information of bubbles to acquire more accurate behavior features. In this paper, the variations of bubble equivalent diameter, volume, velocity and trajectory in the rising process are estimated, and the factors affecting bubble behavior characteristics are analyzed. It is shown that the method is real-time and valid, the equivalent diameter of the rising bubble in the stagnant water is periodically changed, and the crests and troughs in the equivalent diameter curve appear alternately. The bubble behavior characteristics as well as the spiral amplitude are affected by the orifice diameter and the gas volume flow.     

Depth Mapping of Integral Images Through Viewpoint Image Extraction With a Hybrid Disparity Analysis Algorithm

Integral imaging is a technique capable of displaying 3D images with continuous parallax in full natural color. It is one of the most promising methods for producing smooth 3D images. Extracting depth information from integral image has various applications ranging from remote inspection, robotic vision, medical imaging, virtual reality, to content-based image coding and manipulation for integral imaging based 3D TV. This paper presents a method of generating a depth map from unidirectional integral images through viewpoint image extraction and using a hybrid disparity analysis algorithm combining multi-baseline, neighborhood constraint and relaxation strategies. It is shown that a depth map having few areas of uncertainty can be obtained from both computer and photographically generated integral images using this approach. The acceptable depth maps can be achieved from photographic captured integral images containing complicated object scene.     

水下二维及三维距离选通成像去噪技术研究

相比传统水下摄像机,水下距离选通成像的作用距离可提高两三倍,同时基于该技术可实现快速高分辨率三维成像,在水底详查、避障导航、海洋科学研究、矿藏开发等方面具有广泛应用前景。虽然距离选通成像可通过空间切片的方式抑制水体的后向散射噪声,实现感兴趣区较高质量的成像,但是,在选通图像中仍不可避免地存在空间切片水体的后向散射噪声,导致图像信噪比和对比度降低,尤其是对于远距离目标或低反射率目标。介绍了针对水下距离选通二维成像及三维成像去噪方面的技术研究。在二维成像方面,一是采用双平台自适应增强算法提高图像对比度,更好地满足人眼视觉要求;二是采用参考水体去噪算法实现含目标图像的水体去噪,提高信噪比。在三维成像方面,针对距离能量相关三维成像,一是利用参考水体去噪算法实现去噪三维重建,二是采用双边滤波法对三维图像中数据空洞进行修复,提高三维图像质量。所述四种方法可独立或联合用于水下距离选通成像的去噪增强,提高水下距离选通成像技术的性能。     

气液两相流中气泡形态及运动特征参数提取

对气泡发生装置中竖直向上气泡的形态及运动特征提取方法进行了研究。采集原始气泡图像,进行图像灰度化、差影和中值滤波等图像预处理,针对气泡图像的特点,提出动态阈值压缩大津法进行阈值分割,并结合扫描线种子填充算法与图像形态学运算进行孔洞填充,同时基于边缘面积属性对气泡特征区域进行自动识别。实验结果表明,该方法简单有效,鲁棒性强,可以很好地将目标气泡从背景中分离出来,有效提取气泡周长、面积、圆形度和质心坐标等形态特征参数,并实现气泡运动速度的测量。     

一种人体体表三维温度场的融合重建方法

重建人体体表三维温度场能够为包括诊断在内的多项人体医学分析提供可靠数据.由于红外成像具有温度测量精度低、成像分辨率不足以及显示效果较差等缺陷,导致重建的目标三维温度场的可靠性存在不足.针对这些问题,提出一种针对人体体表的三维温度场的融合重建方法.即首先采用黑体测温标定的方法,对红外热像仪的测温结果进行误差修正;其次对红...     

2D/3D 距离选通成像的低对比度目标探测

低对比度目标探测在司法取证、反恐维安、远距离监控、搜救等应用中具有重要意义,然而传统二维成像方法则难以对其有效探测。由此,提出了基于2D/3D 距离选通成像探测低对比度目标的方法:通过2D 距离选通成像直接获取目标无背景或背景部分滤除的二维选通图像,从而突显目标,简化目标提取图像处理;当复杂背景无法有效滤除时,可进一步通过3D 距离选通成像重建二维选通图像中丢失的三维空间信息,通过距离图区分目标与背景,实现目标有效探测。在该方法中,3D 距离选通成像是基于上述二维选通图像采用超分辨率三维成像反演实现的,因此无需耗时获取新数据,从而提高了实时性,并压缩了数据量。研究和实验表明:该方法可有效解决低对比度目标探测问题,在低照度及恶劣天气环境下均可有效工作。     

指静脉红外图像特征不变性编码新方法

基于编码的特征表达方法在光照不变性、运算效率、特征表述能力等方面具有较大优势,成为新型的特征提取方法之一。手指静脉图像采用红外光透射成像,加之手指内部其他组织的固有影响,图像质量普遍较低。将Gabor滤波对图像纹理的增强与局部图结构编码的思想相结合,重点研究一种新的对称邻域交叉图结构,将局部邻域的纹理变化转换为加权的编码串。通过不同方向特征编码提取每个通道Gabor滤波图像的特征编码图,充分表达像素点周围邻域的位置信息和梯度信息,具有良好的旋转不变性。实验结果表明:提出的手指静脉特征编码新方法比多种常用特征编码方法具有更好的识别性能,对图像姿态变化更鲁棒。     

基于条纹投影的双目结构光成像系统

研究了一种 基于条纹投影 的双目三维成像方法,实现对表面有大梯度或非连续等复杂形貌物体的测量。计算机软件产 生的正弦条纹 经DLP投影仪投射到被测物体表面,左右两个CCD相机同时拍摄经被测物体表面调制的变形条 纹图。通过 四步相移和最佳条纹选择方法分别计算得到折叠相位图和展开相位图。建立绝对相位与深度 之间的关系, 得到两组不同坐标系下的三维点云数据。提出一种改进的最近点迭代(ICP)算法,在每一次 迭代过程中剔除 不可见点和噪声点,将两组点云数据转换到同一坐标系中。三维形貌测量实验证明了所研制 成像系统的可 行性和准确性。视场范围内的最大测量误差为0.072mm。     

用于海洋宏生物原位观测的水下激光雷达相机

海洋宏生物原位“观”和“测”对于海洋生态环境、海洋生物资源和海底矿产资源的研究和评估具有重要的意义。目前用于海洋宏生物原位观察的传统水下摄像机存在目标辐射特性、水体光散射、距离信息丢失等导致的低对比度目标探测难的问题。针对此,提出了水下激光雷达相机,可以兼顾并超越传统激光扫描雷达与摄像机复合的技术方案,利用单一系统同时获得百万像素高对比度的二维强度图像和高分辨率的三维图像,且二维图像中的像素和三维图像中的体素一一对应,并介绍了基于该技术研制的“凤眼”系统,其光立体采样区体积可调,距离分辨率优于1 cm,像素数为1360×1024。自2018年起,“凤眼”在我国南海海域进行了4个航次的海上试验,获取了海底宏生物及微地形地貌图像,最大工作深度达到3 291 m。     

一种基于非参数模型的相机内参校准方法

影响大空间视觉三维坐标测量不确定度的主要因素有相机内参数、外部方位参数和特征成像质量.传统相机内参数校准方法需要参数模型化及全局最优化求解方法,会造成各内参数相关性过高,局部校准误差较大,对基于测角的测量方式不确定度影响较大、结合相机成像原理及垂线法,提出了一种基于物理参数校准的方法,对主点位置偏移、全视场范围非均匀镜头畸变等参数进行了精细校准.最后,以交比不变误差作为相机校准精度的评价方法,与传统校准方法的对比实验表明,该校准方法能够有效地提高测量不确定度指标,是一种简单、实用的校准方法.     

3D shape from focus using LULU operators and discrete pulse transform in the presence of noise

3D shape recovery is an interesting and challenging area of research. Recovering the depth information of an object from a sequence of 2D images with varying focus is known as shape from focus. Focus value of an image carries information about the object and shape from focus is a method which depends on different focused value images. It reconstructs the shape/surface/depth of an object based on the different focused values of the object. These different focused valued images should be captured from the same angle. Calculating the shape of the object from different images with different focused values can be done by applying sharpness detection methods to maximize and detect the focused values. In this paper, we propose new 3D shape recovery techniques based on LULU operators and discrete pulse transform. LULU operators are nonlinear rank selector operators that are efficient with low complexity. They hold consistent separation, total variation and shape preservation properties. Discrete pulse transform is a transform that decomposes image into pulses. Therefore selection of right pulses, give sharpest focus values. The proposed techniques provide better result than traditional techniques in a noisy environment.     

集成成像同名像点自筛选技术

从集成成像三维获取技术出发,利用光线追迹的方 法,理论分析了元素图像阵列中同名像点之间的关联性,得到了同名像点之间的等差关系, 并利用此关系式对光学获取的元素图像阵列提取的同名像点的结果进行筛选,去除误差大的 配准结果,从 而提升同名像点的配准精度。光学实验结果显示,对于同一物体进行三维获取,经本文的集 成成像 同名像点自筛选技术得到的结果是500mm,相对误差为0.4% ;而传统技术重构得到的结果为502mm,相对 误差为0.8%。我们所提的这种方法有效提升了再现精度,提升幅度为 50%,为集成成像三维形貌获取技术实现高精度获取提供了有效的技 术支持。     

Multimodality Image Registration Using Spatial Procrustes Analysis and Modified Conditional Entropy

In this paper, we propose a new image registration technique using two kinds of information known as object shapes and voxel intensities. The proposed approach consists of two registration steps. First, an initial registration is carried out for two volume images by applying Procrustes analysis theory to the two sets of 3D feature points representing object shapes. During this first stage, a volume image is segmented by using a geometric deformable model. Then, 3D feature points are extracted from the boundary of a segmented object. We conduct an initial registration by applying Procrustes analysis theory with two sets of 3D feature points. Second, a fine registration is followed by using a new measure based on the entropy of conditional probabilities. Here, to achieve the final registration, we define a modified conditional entropy (MCE) computed from the joint histograms for voxel intensities of two given volume images. By using a two step registration method, we can improve the registration precision. To evaluate the performance of the proposed registration method, we conduct various experiments for our method as well as existing methods based on the mutual information (MI) and maximum likelihood (ML) criteria. We evaluate the precision of MI, ML and MCE-based measurements by comparing their registration traces obtained from magnetic resonance (MR) images and transformed computed tomography (CT) images with respect to x-translation and rotation. The experimental results show that our method has great potential for the registration of a variety of medical images.     

Volume rendering of 3D medical ultrasound data using direct feature mapping

The authors explore the application of volume rendering in medical ultrasonic imaging. Several volume rendering methods have been developed for X-ray computed tomography (X-CT), magnetic resonance imaging (MRI) and positron emission tomography (PET). Limited research has been done on applications of volume rendering techniques in medical ultrasound imaging because of a general lack of adequate equipment for 3D acquisitions. Severe noise sources and other limitations in the imaging system make volume rendering of ultrasonic data a challenge compared to rendering of MRI and X-CT data. Rendering algorithms that rely on an initial classification of the data into different tissue categories have been developed for high quality X-CT and MR-data. So far, there is a lack of general and reliable methods for tissue classification in ultrasonic imaging. The authors focus on volume rendering methods which are not dependent on any classification into different tissue categories. Instead, features are extracted from the original 3D data-set, and projected onto the view plane. The authors found that some of these methods may give clinically useful information which is very difficult to get from ordinary 2D ultrasonic images, and in some cases renderings with very fine structural details. The authors have applied the methods to 3D ultrasound images from fetal examinations. The methods are now in use as clinical tools at the National Center of Fetal Medicine in Trondheim, Norway.     

Three-dimensional modeling from endoscopic video using geometric constraints via feature positioning

The endoscope is a popular imaging modality used in many preevaluations and surgical treatments, and is also one of the essential tools in minimally invasive surgery. However, regular endoscopes provide only 2-D images. Even though stereoendoscopy systems can display 3-D images, the real anatomical structure of the observed lesion is unavailable and can only be judged by the surgeon's imagination. In this paper, we present a constraint-based factorization method for reconstructing 3-D structures registered to the patient, from 2-D endoscopic images. The proposed method incorporates the geometric constraints from the tracked surgical instrument into the traditional factorization method based on frame-to-frame feature motion on the endoscopically viewed scene. Experiments with real and synthetic data demonstrate good real-scale 3-D extraction, with greater accuracy than is available from traditional methods. The reconstruction process can also be accomplished in a few seconds, making it suitable for on-line surgical applications to provide surgeons with additional 3-D shape information, critical distance monitoring and warnings.     

Robot Vision System for Coordinate Measurement of Feature Points on Large Scale Automobile Part

In this paper, we present a robot vision based system for coordinate measurement of feature points on large scale automobile parts. Our system consists of an industrial 6-DOF robot mounted with a CCD camera and a PC. The system controls the robot into the area of feature points. The images of measuring feature points are acquired by the camera mounted on the robot. 3D positions of the feature points are obtained from a model based pose estimation that applies to the images. The measured positions of all feature points are then transformed to the reference coordinate of feature points whose positions are obtained from the coordinate measuring machine (CMM). Finally, the point-to-point distances between the measured feature points and the reference feature points are calculated and reported. The results show that the root mean square error (RMSE) of measure values obtained by our system is less than 0.5 mm. Our system is adequate for automobile assembly and can perform faster than conventional methods.     

非视域成像技术分析与展望（特邀）

传统的光学成像技术受限于信息获取和处理方式,只能对视域范围内的目标进行成像。伴随着新型成像设备和高性能计算方法的发展,集光学成像、计算技术和图像处理于一体的非视域成像技术（none-line-of-sight,NLOS）使超越视域范围成像成为可能。文中依据成像机理的差异,将现有非视域成像技术分为三类:基于相干信息的方法、基于二维强度信息的方法和基于光子飞行时间的方法,详细分析了不同成像方法的原理及实现。同时将基于光子飞行时间的方法作为综述重点,在包含多类型目标和室内外场景的公共数据集中,定量比较了代表性方法的成像性能,并进一步设计搭建了阵列式非共焦瞬态成像装置,单曝光采集了真实场景中的非共焦瞬态图像,分析了典型非共焦成像方法在该成像架构下的重建能力。最后讨论了非视域成像技术的未来发展方向并展望了其应用前景。     

旋流火焰三维温度场与速度场的同时激光测量

燃烧诊断与流场显示领域的研究热点已延伸至研发同时满足非侵入式、多参量同步测量、定量计算、多维可视化等技术要求的显示、测量新方法。研究复杂燃烧三维温度场和速度场的同时激光测量,表征燃烧化学反应和流场输运的重要特性。提出一种光偏折层析测温方法与粒子图像测速方法相结合的燃烧多参量场激光测量方法。设计温度场和速度场激光测量的实验系统,获取4方向莫尔偏折条纹和4幅火焰粒子图像。同时重建与可视化旋流燃烧温度分布和速度云图、流线、涡量等流场,并分析不同工况下的旋流火焰特性。对直接测量数据与重建结果进行对比,验证了所提方法的有效性。     

基于主动式全景视觉的管道形貌缺陷检测系统

针对现有的管道缺陷检测技术不能同时对管道的形、貌缺陷进行检测与评估这一工程难题,在前期研究工作的基础上,设计了一种基于主动式全景视觉的管道内部缺陷检测系统,能够快速获取管壁密集点云的三维坐标,同时对内壁表面缺陷进行检测与评估。首先利用主动式全景视觉传感器（AODVS）实时获取内壁全景图像和激光横断面扫描全景图像,然后对管道内壁全景图像进行柱状展开、预处理和缺陷检测及分类等处理;然后对激光横断面扫描全景图像处理,计算管道内壁点云的三维坐标,进一步对管道缺陷部分进行定量分析,最后利用三维建模技术重构带有真实纹理信息的管道模型。实验结果表明:文中设计的检测系统能够对管道凹凸形变、孔洞、管壁裂缝、腐蚀等缺陷进行检测与分析,具有较高的检测精度,为管道内表面三维测量和重构提供了一种新的手段。     

High dynamic range imaging with short- and long-exposures based on artificial remapping using multiscale exposure fusion

High dynamic range imaging (HDRI) is an excellent high-quality image acquisition technique, which can reflect real human visual characteristics from one (or several) captured low dynamic range (LDR) image. However, the input LDR image only provides partial information of the scene. Besides, in traditional HDRI methods that require multiple captured images as input, field of view errors can be induced, which will be difficult to apply it to the emerging image acquisition systems. Here, we propose a novel HDRI method that reconstructs an HDR image from only a pair of short- and long-exposure images based on artificial remapping using multi-scale exposure fusion. Firstly, we introduce a simulated exposure model called artificial remapping to synthesize a multi-exposure image sequence from the input LDR image pairs. Then, weighting maps of the sequence for fusion can be obtained according to the evaluation factors of contrast, saturation, as well as improved exposedness. Finally, we utilize the pyramid based multiscale exposure fusion framework to integrate them into an enhanced HDR image. Comparative experiments, fully implemented on some source images, have been demonstrated that better performance can be realized compared with some competing methods in qualitative and quantitative evaluation. Note that the operation of the proposed method is simple yet effective, which is easy to popularize. The method thus can be potentially applied to the emerging image acquisition systems where two images are captured simultaneously by two image sensors or by one image sensor with a pair of short- and long-exposure setting.