一种改进的SAR图像LEE滤波算法

针对SAR图像相干斑滤波中存在的降低相干斑与有效保持细节信息这一矛盾,研究了常用空域滤波算法,在此基础上,将中值滤波与增强LEE滤波相结合,改进了LEE滤波算法,该方法能够在滤除相干斑的同时很好地保持图像的边缘及细节纹理信息。     

SOM‐based projection module for mobile displays

Abstract— The development of a compact, efficient VGA projection module to be embedded in mobile devices is reported. The design incorporates laser/laser diode (LD) light sources, Schlieren optics, and a one‐dimensional diffractive spatial optical modulator (SOM). During development, the optical parameters were determined and the relationships between the parameters to optimize the optical specifications were derived. The resulting optimized specifications enable us to manufacture two types of optical modu les as compact as 13 cc and with as little as 10% speckle contrast ratio.     

改进权值非局部均值超声图像去噪

目的 超声图像斑点噪声会影响诊断的准确性和可靠性。通过分析超声图像斑点噪声统计模型,结合非局部均值滤波算法,提出一种基于超声斑点噪声模型的改进权值非局部均值（NLM）滤波算法。方法 算法针对超声图像灰度信息对图像进行预处理,利用超声图像斑点噪声模型改进传统NLM算法的权值计算函数,基于图像特征确定最优采样间隔进行下采样,利用改进后的权值计算函数对图像进行NLM去噪处理。结果 分别采用人工合成与真实超声图像对本文算法性能进行测试,并与传统非局部均值滤波算法、非局部总变分（NLTV）等算法进行去噪效果比较,同时采用均方误差、峰值信噪比和平均结构相似性作为滤波算法性能的客观评价指标。本文算法能快速完成超声图像的去噪处理,峰值信噪比较其他算法可以提高0.2 dB以上,可以降低均方误差,提高平均结构相似性,缩短处理时间,并得到较好的图像质量和视觉效果。结论 根据超声图像斑点噪声模型对NLM算法的权值计算函数进行优化,使得NLM图像滤波算法能更好地适用于超声图像的去噪,基于超声斑点噪声模型的改进权值NLM算法相较于其他算法,滤波效果更佳,适合超声图像去噪。     

Simultaneous speckle reduction and contrast enhancement for ultrasound images: Wavelet versus Laplacian pyramid

Speckle can be described as random multiplicative noise. It hampers the perception and extraction of fine details in the image. Speckle reduction techniques are applied to ultrasound images in order to reduce the noise level and improve the visual quality for better diagnoses. It is also used as preliminary treatment before segmentation and classification. Several methods have been proposed for speckle reduction in ultrasound images. Multiscale contrast enhancement has proven to be very efficient for x-ray images. A recent study by Dippel et al. doing a comparison, contrast enhancement of radiographs (x-ray and mammography), between the Laplacian pyramid and the wavelet one proves that the Laplacian pyramid method gives a better result than the wavelet one; the filtering aspect was not taken into account. In ultrasound images a strong contrast variation exists which is different from x-ray and mammography. In this paper a wavelet pyramid with simultaneous speckle reduction and contrast enhancement was applied for the first time on ultrasound images with the area of interest and compared to a Laplacian enhancement pyramid. The optimum choice of wavelet bases for ultrasound images is investigated in this study. In order to realize a fair comparison, the same nonlinear modification in both multiscale schemes is used. The comparison proves that the wavelet pyramid gives a much better result than the Laplacian one for simultaneous speckle reduction and contrast enhancement of ultrasound images. The text was submitted by the author in English. Ali Samir Saad, 1964. 1996 PhD in image processing, Polytechnics School of the Engineering University of Nantes, France. 1993 Masters in Electronics. 1990 Masters in Digital Image Processing, Institute of Computer Sciences and Communication University of Rennes, France. 1989 BS in Electrical Engineering, University of Saint-Etienne. Academy of Lyon, France. 1996–2000 Research associate at the National Center for Macromolecular Imaging. Baylor, Houston, Texas. Assistant professor at King Saud University, Dept. of Biomedical Technology. Area of research in medical image processing and analysis, 23 publications, member of the American Association for the Advancement of Sciences. Marquis Who’s Who in the World; Cambridge Blue Book 2006.     

基于多尺度自适应小波阈值的SAR图像降噪

为了抑制合成孔径雷达(synthetic aperture radar,SAR)成像系统所固有的相干斑噪声,提出一种小波域的多尺度自适应阈值滤波算法.本算法基于BayesShrink阈值,利用多尺度小波系数的局部统计量估计参数和阈值,并结合空域增强Lee算法的思想,平滑均匀区域,保留斑点发育不完全区域.实验结果表明,相对于传统的空域滤波算法、小波软阈值去噪算法和BayesShrink软阈值算法,本算法等效视数(equivalent number of looks,ENL)和边缘保持指数最高,能有效抑制斑点噪声,并且很好地保存了边缘细节。     

数字散斑相关法在SEM观测岩石变形时的应用

通过带扫描电镜的伺服实验机对岩石进行了原位拉伸观测实验,实时采集了岩石变形破坏过程中表面细观形貌的扫描电镜(SEM)照片.将亚像素插值和相关系数插值相结合,有效提升了数字散斑相关法的搜索效率和计算精度,并通过自行研发的数字散斑相关方法(DSCM)程序实现了岩石SEM图像中微小变形的分析计算.通过对比实验测定结果和软件计算结果,验证了算法的有效性.结果表明:岩石变形具有明显的非均匀性,在整体受拉的情况下局部出现受压区,其原因在于应力集中或损伤软化现象,且随着载荷的增加,损伤逐渐加剧并导致应变集中,从而诱发断裂.     

激光剪切散斑检测技术在飞机复合材料检测中的应用

针对目前采用敲击法检测飞机复合材料存在可靠性差,检测灵敏度低等缺陷,本文采用激光剪切散斑检测系统对飞机复合材料进行检测,并应用该系统对含损伤的多层粘接复合材料及双层蜂窝粘接复合材料试件进行了检测试验。试验结果表明,激光剪切散斑检测灵敏度高,结果直观,不漏检,可以定量测量缺陷的尺寸,精度达0．1mm,可以测量纵向变形,精度达0．1μm,还可以测量缺陷之间的距离。该系统无需专门隔振,具有计算机实时图像记录等特点,对飞机复合材料的检测具有较好的效果。     

基于对数压缩的超声各向异性扩散去噪方法

针对当前超声图像去噪算法很难同时做到降噪和边缘保持的情况,在进行各向异性扩散模型研究的基础上,提出基于对数压缩的改进各向异性扩散算法（LCAD）去除超声散斑噪声。算法将图像对数压缩后进行噪声分布模型估计,然后构造基于广义伽马分布的扩散系数,在扩散过程中达到降噪和边缘保持效果。     

基于ICA的极化SAR图像相干斑抑制

根据极化SAR图像的特点,针对传统空域滤波方法总存在降低相干斑与有效保持边缘纹理信息这一对矛盾,探讨了基于独立分量分析的极化SAR图像相干斑抑制技术,研究了两种基于ICA的极化SAR图像相干斑抑制方法,并分析了其优缺点及应用条件。实验结果表明:基于独立分量分析的方法能有效降低相干斑噪声,较好地保留边缘纹理信息,是一种有效的相干斑抑制方法。     

数字散斑相关技术中散斑颗粒尺寸大小对测量精度影响的研究

通过选取不同颗粒尺寸大小的散斑场针对不同距离,不同位移情况下进行了实验研究比较,给出了散斑颗粒尺寸大小对测量精度的影响.并以实验结果的相对误差为依据,为将数字散斑相关测试技术实际用于大型建筑工程安全检测时散斑场的人工制作提供一个可靠的实验参考依据.