Quantitative phase retrieval in X‐ray Zernike phase contrast microscopy

In recent years, increasing attention has been devoted to X‐ray phase contrast imaging, since it can provide high‐contrast images by using phase variations. Among the different existing techniques, Zernike phase contrast microscopy is one of the most popular phase‐sensitive techniques for investigating the fine structure of the sample at high spatial resolution. In X‐ray Zernike phase contrast microscopy, the image contrast is indeed a mixture of absorption and phase contrast. Therefore, this technique just provides qualitative information on the object, which makes the interpretation of the image difficult. In this contribution, an approach is proposed for quantitative phase retrieval in X‐ray Zernike phase contrast microscopy. By shifting the phase of the direct light by π/2 and 3π/2, two images of the same object are measured successively. The phase information of the object can then be quantitatively retrieved by a proper combination of the measured images. Numerical experiments were carried out and the results confirmed the feasibility of the proposed method. It is expected that the proposed method will find widespread applications in biology, materials science and so on.     

Object plane detection and phase-amplitude imaging based on transport of intensity equation

By using transport of intensity equation (TIE), phase distribution of an object is retrieved from through-focus intensity images. This technique allows simple and robust phase imaging compared with an interferometric approach. However, it is hard to measure phase distribution when a dynamic object moves in the direction of an optical axis. To clear this problem, autofocusing TIE which is based on local statistics is proposed. The proposed technique achieves the detection of the object plane and the retrieval of a focused object phase distribution simultaneously. In this approach, an object plane is determined by the focusing techniques based on local statistics such as variance, gradient, and Laplacian of amplitude distribution, after phase distribution in an image sensor plane is retrieved by the TIE. The performance of these three statistics is evaluated in numerical and optical experiments, and a suitable focus value is determined for precise phase imaging.     

基于互信息改进型脉冲耦合神经网络多值图像分割

为了自动地进行图像的多值分割,从原始图像与分割图像之间的相互关系出发,以最大互信息为优化分割目标,以互信息熵差作为一种新的分类类数判据,在对传统脉冲耦合神经网络模型改进的基础上,提出了一种基于最大互信息改进型脉冲耦合神经网络图像多值分割算法.理论分析和实验结果表明,该方法能够自动确定最佳分割迭代次数及最佳分割灰度类数,对分割图像具有良好的特征划分能力,且在分割类数较少的情况下,能较好地保持图像细节、纹理及边缘等信息,对不同图像分割准确度高,具有较强的适用性.     

Co-registration method for photoacoustic imaging and laser speckle imaging

Combining photoacoustic (PA) imaging with laser speckle (LS) imaging (LSI) can simultaneously determine total hemoglobin concentration (HbT), hemoglobin oxygen saturation (SO2), and blood flow rates. Thus,the co-registration of PA and LS images is important in physiological studies and pathological diagnosis.This letter presents a co-registration algorithm combining mutual information with the maximum betweenclass variance segmentation method (Otsu method). The mutual information and Otsu method are used to provide the registration measure criterion and image feature recognition, respectively. The evaluation results show that the registration function possesses a single maximum peak and high smoothness across the global co-registration district, indicating a robust behavior. Moreover, this method has good registration accuracy, and the fusion result simultaneously visualizes the separate functional information of two kindsof images.     

Determination of skeleton and sign map for phase obtaining from a single ESPI image

A robust method of determining the sign map and skeletons for ESPI images is introduced in this paper. ESPI images have high speckle noise which makes it difficult to obtain the fringe information, especially from a single image. To overcome the effects of high speckle noise, local directional computing windows are designed according to the fringe directions. Then by calculating the gradients from the filtered image in directional windows, sign map and good skeletons can be determined robustly. Based on the sign map, single image phase-extracting methods such as quadrature transform can be improved. And based on skeletons, fringe phases can be obtained directly by normalization methods. Experiments show that this new method is robust and effective for extracting phase from a single ESPI fringe image.     

An improved gradient-based dense stereo correspondence algorithm using guided filter

This paper presents an improved gradient-based real-time stereo correspondence algorithm using guided filter. Color intensity value is sensitive to radiometric distortions including exposure differences and illumination differences, thus the error correspondence rates of these methods are high. deMaeztu et al. [1] proposed to measure the similarity between pixels using the gradient value instead of color intensity. The method has better robustness to radiometric distortions than intensity-based local methods, but the running time is so long that it is not suitable for real-time applications, because the adaptive support weight of neighbor pixels depends on bilateral filter. Guided filter has edge-preserving character as bilateral filter, but runs faster than it, we use guided filter as adaptive support weight instead of bilateral filter of the neighbor pixels in a finite squared support window. The experimental results demonstrate that the improved algorithm performs much better compared with gradient-based method and other local methods, whether in accuracy or efficiency, according to the widely-used Middlebury stereo benchmarks, and the robustness to radiometric distortions of ours is better also.     

QuickBird数字遥感图像光谱辐射定标

通过高分辨率的QuickBird数字遥感图像辐射定标的基础工作,包括数字图像的物理属性、数字图像的数学基础及注记、图像数据格式等,利用洪河幅QuickBird数字遥感图像记录的来自地气系统的光谱辐射亮度信息,提出辐射定标的计算方法。运用像元DN值转换为波段积分辐射亮度,然后再计算光谱辐射亮度,该辐射定标后的QuickBird图像体现了各种地物的光谱特征的定量信息,QuickBird图像只有经过定标才能与其他传感器图像定量比较分析,从而使反演图像具有应用价值。其意义是为下一步对所需要的专题信息提取进行的图像融合和增强处理提供重要的基础条件,为遥感图像的反演提供了地物光谱信息,这样把对地物波谱特征的研究与建立遥感应用模型结合起来,从而达到对地物定量分析的目的。     

Extended gravitational pose estimation

The model-to-image registration problem is a problem of determining the position and orientation (the pose) of a three-dimensional object with respect to a camera coordinate system. When there is no additional information available to constrain the pose of the object and to constrain the correspondence of object features to image features, the problem is also known as simultaneous pose and correspondence problem, or correspondenceless pose estimation problem. In this paper, we present a new algorithm, called extended gravitational pose estimation (EGPE), for determining the pose and correspondence simultaneously. The algorithm is based on gravitational pose estimation (GPE) algorithm. In our algorithm, the original GPE has been revised to deal with the problem with false image points. For problems with both occluded object points and false image points, we firstly applied single-link agglomerative clustering algorithm to pick out occluded object points when a local minimum has been found, then the revised GPE is applied again on the clustering result to update rotation and translation of the object model. EGPE has been verified on both synthetic images and real images. Empirical results show that EGPE is faster, more stable and reliable than most current algorithms, and can be used in real applications.     

Quantification of trabecular structure in the distal femur using magnetic resonance phase imaging

A new approach for quantifying trabecular bone tissue using the phase images of a simple gradient-echo sequence is presented. The proposed method is based on the hypothesis that the differences in susceptibility between bone and bone marrow cause magnetic field (i.e., precession phase) variations between the image voxels. Phase images of the distal femur were obtained in vivo and characterised with the use of the phase variance. Computer simulations and experimental results indicate that the distribution of the phases varies with echo time and image resolution, as expected. Keeping these fixed, however, the phase variance is found to strongly reflect variations in trabecular structure.     

Rapid and robust medical image elastic registration using mean shift algorithm

In landmark-based image registration, estimating the landmark correspondence plays an important role. In this letter, a novel landmark correspondence estimation technique using mean shift algorithm is proposed. Image corner points are detected as landmarks and mean shift iterations are adopted to find the most probable corresponding point positions in two images. Mutual information between intensity of two local regions is computed to eliminate mis-matching points. Multi-level estimation (MLE) technique is proposed to improve the stability of corresponding estimation. Experiments show that the precision in location of correspondence landmarks is exact. The proposed technique is shown to be feasible and rapid in the experiments of various mono-modal medical images.     

半色调编码计算全息图的数字水印方法

提出一种新的基于信息光学的数字水印方法。该方法将水印信息隐藏于半色调编码的计算全息图之中。通过相位复原技术将需隐藏的水印信息编码为相位函数嵌入在复波前中,其振幅定义为宿主图像,通过计算全息记录复波前并对全息图进行半色调编码完成水印信息的嵌入。水印的提取过程只需对含有水印信息的半色调图像进行光学或数字的傅里叶变换即可完成。并给出了算法有效性的理论分析和仿真实验结果。结果证明这种水印技术对于各种数字图像处理操作具有很高的稳健性,且半色调编码图的二值特性使嵌入水印具有很强的抗打印、抗复印、抗扫描的能力。     

A method on calculating high-dimensional mutual information and its application to registration of multiple ultrasound images

Using mutual information as a criterion for medical image registration, which requires no prior segmentation or preprocessing, has been both theoretically and practically proved to be an effective method in these years. However, this technique is confined in registering two images and hard to apply to multiple ones. The reason is that unlike mutual information between two variables, high-dimensional mutual information is ill defined. In textbooks and theoretical essays, three-dimensional mutual information is proposed based on Venn diagram. Unfortunately, mutual information defined in this way is not necessarily nonnegative. In order to overcome the problem, in this paper, we introduce the mutual information matrix. By calculating its eigenvalues, high-dimensional mutual information is defined. This definition is nonnegative, bounded, and could be extended to higher dimensions, thus enables us to register more than three images. In the end, this definition is tested and proved to be effective on registration of multiple US images through simulation.     

Estimation of the vanishing point in camera-mirror scenes from video

Knowledge of the position of the vanishing point is the key for geometrical modeling of an image containing a reflective surface or cast shadows. Such an image can be analyzed as two subimages that constitute a stereo pair. For this model-estimation task an automatic method is presented that utilizes motion statistics and the statistical properties of image points for the determination of point correspondence and the subsequent estimation of vanishing point position, optimized by use of a goodness-of-fit function. We show that this approach gives robust results in widely different real-world environments, even when the correspondence is corrupted with considerable amounts of noise.     

Human eye iris recognition using the mutual information

This article presents the new biometric electro-optical measuring method supported by PC for identification of a person by its eye iris image recognition. The aim of this approach is to show the ability of mutual information to such recognition. Couples of the comparative human iris images were geometrically aligned by maximization of their mutual information and subsequently recognized. The mutual information was estimated using the efficient algorithm proposed by G. A. Darbellay and I. Vajda. The decision whether two compared iris images belong to the same eye depends on the chosen threshold of the mutual information. Only a simple preprocessing of the iris images is needed to acquire their characteristic geometric parameters before the recognition is performed. The investigations carried out showed the correct (successful) personal identification better than 99%.     

Study of mutual information multimodality medical image registration based on modified simplex optimization method

Because of a different imaging mechanism and highly complexity of body tissues and structures. Different modality medical images provide non-overlay complementary information. This has very important significance for multimodal medical image registration. Image registration is the first and key part of problem to be solved in the integrations. When the spatial position of two medical images is same, the registration could be achieved. For two CT and PET images, the principal axis method is adopted to achieve the rough registration. The modified simplex algorithm is employed to implement global search using the mutual information as similarity measure. The initial registration parameters are achieved through principal axis Based on the results of test, improved simplex method can adjust reflecting distance. Stepped-up optimization algorithm on the new experimental points through the methods of “reflection”, “enlargement”, “shrinkage” or “global systolic”. A mutual information registration based on modified simplex optimization method is presented in this paper to improve the speed of medical image registration.Results indicate that the proposed registration method prevents the optimizing process from falling into local extremum and improves the convergence speed while keeping the precision. The accurate registration of multimodal image with different resolutions is achieved.     

数字全息显微术中重建物场波前的相位校正

数字全息显微术克服了传统光学显微术无法直接提取样品相位信息的缺点,可以对活体细胞组织等相位型生物样品进行定量测量和有效观察。但在数字全息显微成像过程中,像场弯曲会对再现像相位分布的测量和观察产生影响。提出一种采用相位相减来校正数字全息再现像像场弯曲的方法。通过在样品加入前后两次拍摄全息图,并对数值重建像分别进行去包裹运算再令其相减,即可实现对像场弯曲的有效校正,对蝉翼和大蒜表皮细胞等相位型物体进行测量,并采用数值校正和相位相减两种方法对像场弯曲进行校正。与现有的数值校正方法相比,利用相位相减获得样品三维相位信息的方法更为简单、可靠,是校正像数字全息再现场弯曲的有效方法。     

基于多尺度均值漂移的高分辨率遥感影像快速分割方法

均值漂移算法是一种特征空间分析方法,广泛应用于自然场景影像和医学影像分割中.但算法较高的计算复杂度成为其在具有海量特性的遥感影像中应用的瓶颈.文章将均值漂移算法拓展到小波域,提出了一种小波域均值漂移快速分割算法.多光谱遥感影像和仿真影像的实验表明:在获得相当的分割结果的前提下,相比单尺度均值漂移算法,提出的分割算法能够...     

基于成像系统物理特性的多光谱图像与全色波段图像融合

提出了一种基于成像系统物理特性的多光谱图像与全色波段图像融合算法。该算法采用àtrous小波变换提取全色波段图像的空间细节信息,并将提取的空间信息按照一定的注入模型调整后添加到各波段多光谱图像中去,得到具有高空间分辨力的多光谱图像。注入模型充分考虑了各波段成像传感器的相对光谱响应函数、地表物体对各波段的光谱反射率以及各波段的辐射调整系数等成像系统的物理特性,使融合后的多光谱图像在显著提高空间质量的同时,最大可能地保留了原始多光谱图像的光谱特性。对IKONOS卫星遥感影像的融合实验结果表明,该算法在光谱保留和空间质量提高方面较其它基于小波变换的融合算法都具有更高的性能。     

结合松弛中值滤波的高阶彩色图像迭代去噪算法

为去除基于局部平均曲率的彩色图像去噪模型中作为几何特征而保留下来的斑点,提出了一种改进的迭代算法。采用局部平均曲率作为正则项耦合各个颜色通道,在迭代过程中根据局部统计量检测斑点,并引入松弛中值滤波进行斑点抑制。使用不同特征的图像进行仿真实验,并对峰值信噪比的演化进行分析。实验结果表明,改进的算法在有效消除斑点的同时较好地保护了图像结构,并且提高了计算效率。峰值信噪比提高了2.47%,迭代次数减少了93.66%。     

Image registration framework for large-scale longitudinal MRI data sets: strategy and validation

Advanced magnetic resonance imaging (MRI) studies often require the transformation of large numbers of images into a common space. Calculating transformations that relate each image to every other and applying them to the images on demand are theoretically possible; however, these can be computationally prohibitive. Therefore, relating each image to only one other image, then linking those transforms together to relate any two images in the database, may be an efficient alternative. Evaluated were the feasibility and validity of image registration to bring intraindividual MR images into mutual correspondence for longitudinal analysis through the concatenation of precomputed transforms. A longitudinal data set of 10 multiple sclerosis patients with nine serial dual-echo spin-echo, 1.5-T MRI scans was used. Intrasubject registrations were performed stepwise between consecutive images and direct from each time point to the baseline. Consecutive transforms were concatenated and evaluated against direct registrations by comparing the resulting transformed images (using Pearson correlation coefficient). Confounding variables such as time between scans, brain atrophy, and change in lesion load were evaluated. We found the images resampled with the direct and the concatenated transforms to be highly correlated, and there was no significant difference between methods. Differences in brain parenchymal fraction (a measure of brain atrophy) showed significant inverse correlation with the correspondence of the resampled images. Results indicate that concatenating multiple transforms that link two images together produces near-identical results to that of direct registration; thus, this method is both useful and valid.