Three dimension double inversion recovery gray matter imaging using compressed sensing

The double inversion recovery (DIR) imaging technique has various applications such as black blood magnetic resonance imaging and gray/white matter imaging. Recent clinical studies show the promise of DIR for high resolution three dimensional (3D) gray matter imaging. One drawback in this case however is the long data acquisition time needed to obtain the fully sampled 3D spatial frequency domain (k-space) data. In this paper, we propose a method to solve this problem using the compressed sensing (CS) algorithm with contourlet transform. The contourlet transform is an effective sparsifying transform especially for images with smooth contours. Therefore, we applied this algorithm to undersampled DIR images and compared with a CS algorithm using wavelet transform by evaluating the reconstruction performance of each algorithm for undersampled k-space data. The results show that the proposed CS algorithm achieves a more accurate reconstruction in terms of the mean structural similarity index and root mean square error than the CS algorithm using wavelet transform.     

基于小波树和哈达玛矩阵的自适应快速三维压缩成像方法

针对光子计数系统实现三维成像速度缓慢的问题,提出一种基于小波树和哈达玛矩阵的自适应快速三维压缩成像方法。利用哈达玛矩阵调制投影图案提高采样效率,被调制的短脉冲结构光照射场景,单像素光子计数探测器采集回波。通过分析低分辨率图像的小波树选择采样区域,使用哈达玛矩阵调制所选采样区域得到的投影图案,可采集图像细节,多阶段采样后利用哈达玛反变换恢复出高分辨率图像。实验结果表明,采集并恢复出一幅512×512像素的三维图像的时间最快可达到41 s。     

光学并行实现模糊逻辑图像处理

提出和验证一种基于偏振－空间编码方案和多重成像技术的光学方法来实现模糊逻辑图像处理,系统中,模糊变量和它们的补被编码为空间正交分布的两个偏振状态。通过对透镜阵列状态的编程,可以实现两个模糊图像间的模糊逻辑操作。本系统中,两个输入图像被偏振编码为8个编码图像作为输入图像,系统是空不变系统,不需要取阈装置和解码过程,通过引进取阈装置,可以在一层系统中实现两个图像间更为复杂的模糊逻辑操作,并给出了实验结果。     

基于SPIHT的图像加密与压缩关联算法

为了研究图像压缩与加密同步进行问题, 本文提出了一种在变换域下的图像加密与压缩关联算法在该算法中, 加密过程发生在小波变换与SPIHT编码之间它充分利用了离散小波变换和基于层次树的集合划分(set partitioning in hierarchical trees, SPIHT)编码属性, 扩散过程被限制在单个子带内部. 此外, 混淆过程保留了SPIHT编码中两个最重要的位和符号位, 它包含了图像的重要信息. 实验结果表明, 算法具有良好的安全性、图像重构视觉质量以及很高的加/解密速度.     

Multiple-image encryption by two-step phase-shifting interferometry and spatial multiplexing of smooth compressed signal

A multiple-image encryption method based on two-step phase-shifting interferometry(PSI) and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order; then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Arnold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing(CS)and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme,only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Arnold transform, inverse discrete wavelet transform, and pixels reordering operation.     

Secret shared multiple-image encryption based on row scanning compressive ghost imaging and phase retrieval in the Fresnel domain

A multiple-image encryption method is proposed that is based on row scanning compressive ghost imaging, (t, n) threshold secret sharing, and phase retrieval in the Fresnel domain. In the encryption process, after wavelet transform and Arnold transform of the target image, the ciphertext matrix can be first detected using a bucket detector. Based on a (t, n) threshold secret sharing algorithm, the measurement key used in the row scanning compressive ghost imaging can be decomposed and shared into two pairs of sub-keys, which are then reconstructed using two phase-only mask (POM) keys with fixed pixel values, placed in the input plane and transform plane 2 of the phase retrieval scheme, respectively; and the other POM key in the transform plane 1 can be generated and updated by the iterative encoding of each plaintext image. In each iteration, the target image acts as the input amplitude constraint in the input plane. During decryption, each plaintext image possessing all the correct keys can be successfully decrypted by measurement key regeneration, compression algorithm reconstruction, inverse wavelet transformation, and Fresnel transformation. Theoretical analysis and numerical simulations both verify the feasibility of the proposed method.     

基于小波-Contourlet变换的Cycle spinning硬阈值图像去噪方法

综合考虑小波变换的特点以及Contourlet变换对二维光滑图像有很好的近似特性和对曲线有更好的"稀疏"表示的特点,提出了一种基于小波-Contorlet变换的图像硬阈值去噪方法,并用Cycle spinning去除图像中小波-Con- tourlet变换平移变异性而产生的伪吉布斯现象。实验结果表明:该方法与采用Cycle spinning的小波和Contourlet去嗓算法相比,PSNR分别提高了0.4～1.6和0.2～1.0。与其它去噪算法相比,这种方法能有效地去除图像中的噪声,具有更高的PSNR值,能更好地保留图像的纹理和细节。     

基于方向角预测三维小波变换的干涉多光谱图像压缩

根据大孔径静态干涉多光谱图像的成像特点,提出一种基于方向角预测的三维小波变换.这种三维小波变换的新颖之处在于它将方向预测结合到三维提升小波中.这样每次提升小波中的预测可在相关性最强的方向上进行而不需总是局限在变换的方向上.实验证明,对于干涉多光谱图像这种方向性很强的立体图像序列,基于方向角预测的三维小波变换比原始三维提升小波变换有明显改进,在相同的量化编码下,基于方向角预测的三维小波变换比原始三维提升小波变换提高1 dB左右.经该种方法压缩的图像的光谱特性也得到明显改善.     

光学可分离小波变换的研究

为改进光学小波变换,提出了光学可分离小波变换的概念。通过对光学小波变换的必要条件进行分析,采用层叠算法和二维可分离小波变换构造方法计算出了尺度和小波函数的二维离散近似序列。将新的母小波引入到光学小波变换中,获得了光学可分离小波变换。通过与现有光学小波变换及二维可分离离散小波变换进行比较说明了其优点。     

A united optimum images fusion based on analysis of color distortion

In remote sensing community, IHS (intensity, hue, and saturation) transform is one of the most commonly used fusion algorithm. A study on IHS fusion indicates that the color distortion cannot be avoided.Meanwhile, wavelet decomposition has a property of frequency division in transform domain. And the statistical property of wavelet coefficient reflects those significant features. So, a united optimal fusion method, which using the statistical property of wavelet decomposition and IHS transform on pixel and feature levels, is proposed. That is, the high frequency of intensity component I is fused on feature level with multi-resolution wavelet in IHS space, and the low frequency of intensity component I is fused on pixel level with optimal weight coefficients. Spectral information and spatial resolution are two performance indexes of optimal weight coefficients. Experiment results show that it is a practical and effective method.     

Content-based image hashing using wave atoms

It is well known that robustness, fragility, and security are three important criteria of image hashing; however how to build a system that can strongly meet these three criteria is still a challenge. In this paper, a content-based image hashing scheme using wave atoms is proposed, which satisfies the above criteria. Compared with traditional transforms like wavelet transform and discrete cosine transform (DCT), wave atom transform is adopted for the sparser expansion and better characteristics of texture feature extraction which shows better performance in both robustness and fragility. In addition, multi-frequency detection is presented to provide an application-defined trade-off. To ensure the security of the proposed approach and its resistance to a chosen-plaintext attack, a randomized pixel modulation based on the R′enyi chaotic map is employed, combining with the nonliner wave atom transform. The experimental results reveal that the proposed scheme is robust against content-preserving manipulations and has a good discriminative capability to malicious tampering.     

二维提升的CDF(1,3)小波结合改进的SPIHT的渐进性无损图像压缩方法

针对传统小波变换计算复杂的缺点和多级树集合分裂算法(SPIHT)编码过程重复运算、存储量大的问题,提出了一种二维提升的CDF(1,3)小波结合改进的SPIHT的渐进性无损图像压缩方法。对整数CDF(1,3)双正交小波变换实现二维提升,利用提升的小波对图像做变换,提高了运算速度、便于硬件实现。对SPIHT算法加以改进,根据各个子图像的不同特点,改变扫描路线,采用四路并行分块处理的方法,提高了编码速度,降低了编解码过程的运算复杂度和时间消耗。利用提升的CDF(1,3)小波变换结合改进的SPIHT实现了渐进性无损图像压缩,证明了二维提升方案的有效性。     

高速双光谱遥感图像传输系统

提出并设计了一种高速舣光谱遥感图像传输系统.对该系统所采用的传输策略,传输帧结构以及时序恢复等问题进行了深入的研究.首先,将双探测器一行数据中有效部分提取后传输,采用行有效标志中断发送的方式在接收端恢复时序,保证了系统输入输出数据、时序的完全一致;接着,采用发送与接收缓存机制,利用时分复用打法将双探测器的数据在单根光纤...     

Enhanced iterative learning control for a piezoelectric actuator system using wavelet transform filtering

For trajectory tracking of a piezoelectric actuator system, an enhanced iterative learning control (ILC) scheme based on wavelet transform filtering (WTF) is proposed in this research. The enhanced ILC scheme incorporates a state compensation in the ILC formula. Combining state compensation with iterative learning, the scheme enhances tracking accuracies substantially, in comparison to the conventional D-type ILC and a proportional control-aided D-type ILC. The wavelet transform is adopted to filter learnable tracking errors without phase shift. Based on both a time-frequency analysis of tracking errors and a convergence bandwidth analysis of ILC, a two-level WTF is chosen for ILC in this study. The enhanced ILC scheme using WTF was applied to track two desired trajectories, one with a single frequency and the other with multiple frequencies, respectively. Experimental results validate the efficacy of the enhanced ILC in terms of the speed of convergence and the level of long-term tracking errors.     

基于Hadamard矩阵优化排序的快速单像素成像

为提升单像素成像速度,提出了基于Hadamard矩阵优化排序的压缩采样解决方案.利用数值仿真和室外实验对提出的5种排序方法进行了对比分析.研究结果表明:按Haar小波变换系数绝对值排序时单像素成像效果最优,排序对应到Walsh序后可利用快速变换重建图像,速度达300帧/秒@64×64像素;最优排序下,采样率25%仍可重建图像,采样速度可提升4倍.针对排序方法与成像信噪比关系,从关联成像角度给出了其物理解释:测量基矩阵元邻域数值相等的区域面积等效于光场二阶相干面积,当光场二阶相干面积随测量基由大到小排序时成像效果最优.本文研究成果可用于提升单像素成像速度,具有实用价值.     

基于Walsh-Hadamard变换的单像素遥感成像

本文提出了基于Walsh-Hadamard变换的单像素成像方案, 并从理论分析、模拟仿真和实验验证三方面分别验证了该方案的可行性. 实验上实现了350-900 nm波段对 距离500 m和5000 m自然目标的128×128 像素成像, 成像速度0.5帧/秒. 研究并讨论了单像素相机方案与计算量子成像方案的差异与共性, 在此基础上分析了基于Walsh-Hadamard变换的单像素成像方案的优势与局限性. 研究表明本方案同时适用于单像素相机和计算量子成像. 由于单像素成像适用于应用在如红外热成像、微波成像等波段, 因此在阵列探测器灵敏度或工艺达不到要求时存在优势. 本文所提出的方案使得单像素成像技术向实际应用迈进了一步.     

新生儿疼痛面部表情识别方法的研究

针对新生儿的疼痛与非疼痛面部表情识别,提出将Gabor变换和支持向量机(SVM)相结合的分类识别方法.对归一化后的大小为112 pixel×92 pixel的新生儿面部图像进行二维Gabor小波变换,提取出412160维Gabor特征;针对Gabor特征向量维数高、冗余大的特点,采用Adaboost算法作为特征选择工具,去除冗余的Gabor特征,从412160维特征中选取出900维Gabor特征;对选取出的Gabor特征用SVM进行疼痛表情的分类识别.该方法综合运用Gabor特征对于面部表情的良好表征能力、AdaBoost算法的特征选择能力以及SVM在处理少样本、高维数问题中的优势.对510幅新生儿的表情图像进行测试的结果表明,疼痛与非疼痛表情的分类识别率达到85.29%,疼痛与安静表情的分类识别率达到94.24%,疼痛与哭表情的分类识别率达到78.24%.     

基于成像机理的小波包变换多聚焦图像融合

由于可见光成像系统的聚焦范围有限,因而在成像过程中,除聚焦良好的物体能生成清晰的图像外,该物体前后一定距离外的所有物体都将呈现不同程度的模糊.为了获得场景内所有物体均清晰的图像,在分析了多聚焦图像成像机理的基础上,提出了一种基于小波包变换的融合方法.它是将成像系统先聚焦在一部分对象上,得到其清晰的图像;然后再将其聚焦在另一部分对象上,得到另一清晰的图像;最后把这两幅实验图像加以融合,从而获得场景内所有物体均清晰的图像.实验结果表明,基于小波包变换的融合方法能够将信号的频带进行多层次划分,对高频成分也能进一步地分解,可有效综合多聚焦图像.     

基于微粒群区域搜索和小波评价的差分式自动聚焦

为进一步提高图像法自动聚焦的性能,提出了一种差分式提取图像边缘的方法,并构造了图像清晰度的小波评价函数,同时利用微粒群（PSO）算法对聚焦区域进行快速搜索。首先,介绍了差分式边缘提取方法及其优势,给出了一种评价区域的选取判据以及基于PSO的高效搜索方法;然后,对小波评价函数参数进行了比较分析和优选;最后,与传统方法进行了对比实验。结果表明,由于采用了差分式提取方法以及新的自适应聚焦窗口和评价函数,聚焦曲线较传统方法具有更高的调焦分辨率,PSO算法的使用使聚焦速度提高了约170 ms,聚焦精度约为2.3μm,同时调焦效果不受初始位置的影响。     

JPEG2000编码系统研究及VLSI实现

提出了一种JPEG2000编码系统结构和VLSI方案.该方案以小波子带为单位,多套并行处理.对JPEG2000标准中各个模块的算法进行了逻辑化简、并行编码等优化.如采用双行并行9/7提升小波分解,条带并行的比特平面编码,简化区间更新和并行归一化算术编码等.各模块均以流水线方式工作,其中的比特平面编码和算术编码采用异步流水线方式动态分配执行时间,加速比均接近于流水段数3.以图像信号产生板送入原始图像,编码后送入PC机进行码流截断和解压缩.该系统在各个压缩率下的信噪比与LuraWave商用压缩软件的差距均在0.8 dB之内,可见改进后的算法可行且有效,像元时钟可达20 MHz.