一种改进的病理显微图像亚像素快速配准方法

针对病理显微图像的快速高精度配准的应用需求,提出了一种改进的亚像素快速配准方法。通过采用对数差值函数对显微图像重叠区域进行信息量评估,由H型对数差值模板配准获取两幅图像像素级的粗定位和有效子图,继而在两幅子图上采用局部上采样相位相关法来获取亚像素级别的配准估计值。该方法利用H型对数差值模板简洁、配准速度快的优点规避了相位相关法计算量随着图像尺寸增大而急剧增长的缺陷,并能够对显微图像进行信息量评估以避免空白图像造成的误配。经实验表明,改进的显微图像配准方法配准精度可达0.01像素,速度为相位相关法的3.7倍（图像大小为2448×2048）,更适合应用于病理显微图像的快速高精度配准。     

无标记印刷品质量在线检测方法研究

印刷品图像配准是实现印刷品自动检测的关键技术。以高分辨率印刷品图像为研究对象,将原始图像分割成多个兴趣区域,将兴趣区域的中心坐标与旋转角作为图像配准参数,通过变步长搜索算法获取被测图像与模板图像之间的最小旋转角;通过仿射变换将待检图像与模板图像进行配准并使用双向差影法计算两者的差影图像;通过二值化阈值与缺陷区域面积阈值进行缺陷识别。实验结果显示：该检测系统对合格品的检测准确率为96%,对不合格品的检测准确率为94%。     

基于区域特征的胶囊图像分割算法

针对胶囊缺陷检测中存在的图像分割效果不理想的问题, 提出了一种基于区域特征的胶囊图像分割算法. 首先将原图像分割成5个子图像, 然后分别在子图图像中分割提取胶囊. 子图图像首先对图像高亮区域作去高光处理、去除噪声, 然后将图像区域的每一行作为一个子区域, 根据胶囊在图像区域中所在的位置特点, 通过判断子区域中链板域与背景域是否存在边界点以及胶囊与链板上的链齿是否连接来识别不同类型的子区域, 寻找子区域中胶囊与非胶囊区域的边界, 然后去除非胶囊区域. 最终对图像区域逐行扫描处理完成后从图像中提取出胶囊. 实验表明该算法与传统方法相比, 不仅速度较快, 准确性和鲁棒性也得到了改善.     

基于DPP改进RANSAC算法的图像拼接

为提高图像拼接时的配准速度和精度,针对鲁棒性模型估计问题,提出一种基于行列式点过程的改进RANSAC算法（Random Sample Consensus）.该方法利用行列式点过程抽样法的全局负相关特性对匹配的特征点进行建模,实现抽样点的均匀化和分散化,剔除一些错误匹配点.用行列式点过程抽取的点集作为RANSAC算法的输入来求取变换矩阵.实验结果表明：该算法相对于传统的RANSAC算法,能够保持较高的精度和鲁棒性,减少传统RANSAC算法迭代次数,显著提升图像自动拼接的计算效率.     

一种SAS图像拼接改进算法

SWF算子提取的特征点对图像尺度和旋转具有不变性,对环境变化、噪声以及仿射变换都具有很强的鲁棒性。本文在基于SIFT算子和RANSAC算法的图像拼接算法的基础上,根据SAS图像分辨率高、相邻帧图像重合度大且只存在平移和旋转变换的特点,对提取稳定特征点和计算拼接图像之间特征点匹配对的过程进行了改进。实际的SAS湖试图像拼接处理结果说明,改进算法提高了拼接算法的速度和图像之间的配准精度,增强了算法的鲁棒性。     

基于SIFT特征和广义紧互对原型对距离的遥感图像配准方法

主要讨论SIFT(Scale Invariant Feature Transform)及其在遥感图像配准中的应用。首先介绍了基于特征点的遥感图像配准的一般框架;针对基于特征点的遥感图像配准中的两个基本问题-鲁棒的特征点提取和特征点匹配,提出了基于SIFT特征点和广义紧互对原型对距离的遥感图像配准新方法,并通过“广义紧互对原型对”的概念,为不同的特征点匹配方法建立了联系。与已有的相关工作相比,该方法可以得到更多的匹配点对和正确的匹配点对。数值试验证明了该方法的有效性和鲁棒性。     

基于局部重叠区域的无显著特征图像配准算法

针对沙漠、戈壁等特征不显著场景在配准过程中存在快速性、精确性等问题,提出一种基于局部重叠区域的特征不显著图像配准方法。首先利用图像标记对待配准图像进行预处理增强其特征,接着通过多相机三维投影对多幅待配准图像重叠区域进行预算,并采用图像掩膜和图像分割技术将重叠区域分割出来,最后对重叠区域使用ORB+GMS（Oriented Brief-Grid-based Motion Statistics for Fast）融合算法进行配准,完成多幅图像的配准工作。基于图像重叠区域的配准避免了无显著特征图像在进行整体配准时精确性低的缺点,并且由于是局部配准,相较于全局配准拥有更快的配准速度。对比传统配准方法和本文提出的改进配准方法,实验结果显示,本文提出的改进方法配准精度在传统配准方法的基础上提升了28%,同时,算法具有更高的鲁棒性和实时性。     

改进的SURF彩色遥感图像配准算法

为了进一步提高彩色遥感图像的配准精度,针对遥感图像配准过程中色彩信息利用率低以及误匹配率高的问题,提出一种改进的SURF(Speeded Up Robust Feature)彩色遥感图像配准算法;该算法首先在对彩色遥感图像进行特征点检测基础上,对特征点描述算子进行改进,以使颜色空间变换后得到的特征点色彩信息添加到原描述算子中,并对特征点描述算子进行归一化处理,以增加算子的独特性和对旋转、尺度、光照的鲁棒性;其次,结合单向匹配和双向匹配的比值,提出了一种最优化阈值选择准则,如果欧氏距离比率小于最优化阈值,完成特征点匹配,得到正确匹配点对,再通过变换矩阵得到配准图像;实验结果表明,在保证实时性的条件下,该算法相比于原SURF算法,准确性和稳定性都有一定提高,具有一定的理论和应用价值。     

基于显著图的输电线路杆塔图像拼接方法

无人机拍摄的输电线路杆塔图像分辨率高且背景复杂,基于传统特征点的拼接算法在背景中检测出大量的特征点增加了图像匹配的时间,影响了杆塔的匹配精度。针对该问题提出了一种既稳定又具有较小时间开销的输电线路杆塔图像自动拼接方法,利用改进的显著性检测算法得到杆塔图像的显著图,将图像的前景与背景分离,减少了背景对图像中杆塔拼接效果的影响;并采用基于定向的加速分割检测特征(FAST)和旋转不变性的二进制鲁棒独立元素特征(BRIEF)描述子(ORB)特征点的图像匹配算法,以提高特征点提取和匹配的速率;最后利用多尺度融合策略得到最终的拼接结果。实验结果表明,所提方法具有较好的拼接效果和拼接效率。     

A robust hybrid method for nonrigid image registration

A nonrigid registration method is proposed to automatically align two images by registering two sets of sparse features extracted from the images. Motivated by the paradigm of Robust Point Matching (RPM) algorithms [1] and [2], which were originally proposed for shape registration, we develop Robust Hybrid Image Matching (RHIM) algorithm by alternatively optimizing feature correspondence and spatial transformation for image registration. Our RHIM algorithm is built to be robust to feature extraction errors. A novel dynamic outlier rejection approach is described for removing outliers and a local refinement technique is applied to correct non-exactly matched correspondences arising from image noise and deformations. Experimental results demonstrate the robustness and accuracy of our method.     

基于Laplace的LSSIM图像配准算法

提出一种基于Laplace变换的图像配准算法. 首先利用经典的角点检测算法提取待匹配图像的特征点或角点; 其次利用相位相关法估算出两幅图像的重叠区域, 以缩小匹配范围; 然后对角点邻域模板区域施行Laplace变换; 最后利用基于改进的SSIM (结构相似性)作为相似性度量准则建立特征点之间的匹配关系. 实验结果表明, 该方法可以很好的完成特征点匹配, 匹配点对充足且具有很高的准确率, 而且对亮度差异具有一定的鲁棒性, 从而保证图像配准精度.     

基于跨接约束的高分辨率SAR 影像与光学影像配准

为了实现高分辨率SAR 影像与光学影像之间自动/半自动配准, 提出了一种新颖、稳健的匹配算法。算法首先利用仿射变换进行SAR 影像和光学影像粗匹配, 简化了整体算法的处理复杂度;然后利用影像边缘稳健性, 使用边缘提取算子分别对SAR 影像和光学影像进行边缘提取, 为后续精匹配做好了数据准备; 最后使用基于边缘纹理跨接约束进行影像之间精匹配, 方法引入了邻域配准约束机制, 很好的解决了经典匹配多峰值效应, 提高了算法稳健性和实用性。以国内机载高分辨率SAR 数据和SPOT 25 PAN 数据为例进行算法验证, 实验结果表明该算法能实现自动/半自动的高分辨率SAR 和光学影像之间的像素级配准。     

基于角点特征和最大互信息的图像配准

基于互信息的配准方法是图像配准领域的重要方法。互信息是图像配准中常用的相似性度量,具有鲁棒、精度高等优点,但基于互信息的配准计算量大,制约了它的实际应用。文章提出一种基于角点和最大互信息配准方法:首先采用间接算法来计算曲率的极大值点,从而能快速准确的提取角点集;接着计算两幅图像角点集间的互信息,最后通过POWELL算法搜索使互信息最大以实现配准。实验表明,该算法计算简单,配准速度快,具有更好的精确性和鲁棒性。     

Comparison of data gap-filling methods for Landsat ETM+ SLC-off imagery for monitoring forest degradation in a semi-deciduous tropical forest in Mexico

A number of methods to overcome the 2003 failure of the Landsat 7 Enhanced Thematic Mapper (ETM+) scan-line corrector (SLC) are compared in this article in a forest-monitoring application in the Yucatan Peninsula, Mexico. The objective of this comparison is to determine the best approach to accomplish SLC-off image gap-filling for the particular landscape in this region, and thereby provide continuity in the Landsat data sensor archive for forest-monitoring purposes. Four methods were tested: (1) local linear histogram matching (LLHM); (2) neighbourhood similar pixel interpolator (NSPI); (3) geostatistical neighbourhood similar pixel interpolator (GNSPI); and (4) weighted linear regression (WLR). All methods generated reasonable SLC-off gap-filling data that were visually consistent and could be employed in subsequent digital image analysis. Overall accuracy, kappa coefficients (κ), and quantity and allocation disagreement indices were used to evaluate unsupervised Iterative Self-Organizing Data Analysis (ISODATA) land-cover classification maps. In addition, Pearson correlation coefficients (r) and root mean squares of the error (RMSEs) were employed for estimates agreement with fractional land cover. The best results visually (overall accuracy > 85%, κ < 9%, quantity disagreement index < 5.5%, and allocation disagreement index < 12.5%) and statistically (r > 0.84 and RMSE < 7%) were obtained from the GNSPI method. These results suggest that the GNSPI method is suitable for routine use in reconstructing the imagery stack of Landsat ETM+ SLC-off gap-filled data for use in forest-monitoring applications in this type of heterogeneous landscape.     

An entropy-based image registration method using image intensity difference on overlapped region

Image registration is a fundamental procedure in image processing that aligns two or more images of the same scene taken from different times, different viewpoints, or even different sensors. It is reasonable to orientate two images by matching corresponding pixels or regions that are considered identical. Based on this concept, this paper proposes a novel image registration method that applies the information theorem on intensity difference data. An entropy-based objective function is then developed according to the histogram of the intensity difference. The intensity difference represents the absolute gray-level difference of the corresponding pixels between the reference and sensed images over the overlapped region. The proposed registration method is to align the sensed image onto the reference image by minimizing the entropy of the intensity difference through iteratively updating the parameters of the similarity transformation. For performance evaluation, the proposed method is compared with the two exiting registration methods in terms of eight test image sets. The experiment is divided into two scenarios. One is to investigate the sensitivity (i.e., robustness) of the objective functions in these three different methods; the other is to verify the effectiveness of the proposed method. Through the experimental results, the proposed method is shown to be very effective in image registration and outperforms the other two methods over the test image sets.     

Improving ICP with easy implementation for free-form surface matching

Automatic range image registration and matching is an attractive but unresolved problem in both the machine vision and pattern recognition literature. Since automatic range image registration and matching is inherently a very difficult problem, the algorithms developed are becoming more and more complicated. In this paper, we propose a novel practical algorithm for automatic free-form surface matching. This method directly manipulates the possible point matches established by the traditional ICP criterion based on both the collinearity and closeness constraints without any feature extraction, image pre-processing, or motion estimation from outliers corrupted data. A comparative study based on a large number of real range images has shown the accuracy and robustness of the novel algorithm.     

基于改进CNN-RANSAC的水下图像特征配准方法

水对光的吸收和散射效应降低了水下图像的质量,水下图像的可视范围受到限制,复杂水下场景下的鲁棒性和精确性问题使得特征提取与匹配成为一项具有挑战性的任务。为了更好地配准水下图像,提出了一种改进CNN-RANSAC的水下图像特征配准方法,首先通过基于深度卷积神经网络的水下图像增强方法对水下图像进行增强预处理,通过水下图像分类数据集迁移学习训练VGGNet-16网络框架,利用修改后的网络框架进行特征提取,生成鲁棒的多尺度特征描述符与特征点,经过特征粗匹配与动态内点选择,使用改进的RANSAC方法剔除误匹配点。在大量水下图像数据集上进行了充分的特征提取和特征匹配实验,与基于SIFT和SURF的配准方法相比,该方法能够检测到更多的特征点,实现了匹配正确率的大幅度提高。     

基于最小生成树的DoG关键点医学图像配准

针对医学图像配准对鲁棒性强、准确性高和速度快的要求,提出一种基于最小生成树的DoG(difference of Gaussian)关键点配准算法。该算法首先从图像上提取DoG关键点,然后将关键点对应的灰度信息融入联合Rényi熵中,最后使用最小生成树来估计联合Rényi熵。新算法结合了DoG关键点的鲁棒性和最小生成树估计Rényi熵的高效性。实验结果表明,在图像含有噪声、灰度不均匀和初始变换范围较大的情况下,该算法在达到良好配准精度的同时,具有较强的鲁棒性和较快的速度。