低剂量CT重建中的双边滤波权值优化新方法

为了提升低剂量CT重建图像质量,本文提出了一种基于投影数据恢复导引的双边滤波权值优化方法.新方法有效地将CT投影数据恢复和图像数据恢复的两种低剂量成像策略进行结合,实现优质的低剂量CT重建.具体而言,本文中投影数据恢复采用三维块匹配滤波进行,图像数据恢复采用双边滤波进行,其中双边滤波权值进行优化设计.在双边滤波权值设计...     

基于Shearlet变换域图像噪声混合滤波方法

在深入分析Shearlet变换理论的基础上,给出具体的Shearlet变换步骤,并提出一种针对图像脉冲噪声的混合滤波方法.该方法首先对噪声图像进行Shearlet多尺度变换,获得高频和低频系数,保留低频系数不变;然后针对Shearlet高频系数能够较好地刻画噪声局部化的性质,设计出一种多尺度、多方向特性的串/并联自适应中值滤波器,对高频系数中噪声进行自适应检测和滤除;最后实现低频系数和滤波后高频系数重构.通过与小波阈值法去噪和开关中值滤波法仿真实验比较可知,该滤波方法对于高强度的脉冲噪声具有较好的处理效果.     

结合像素域JND阈值空间相关性与图像块类型的残差滤波算法

为了更好地将人眼视觉感知特性应用于视频压缩系统,从而去除视频的视觉冗余成分,在利用像素域的恰可察失真(Just Noticeable Distortion,JND)阈值的基础上,结合JND阈值的空间相关性与图像块类型,提出了一种改进的残差滤波算法。该算法首先在像素域计算出每个像素的JND阈值,然后在变换单元(Transform Unit,TU)中挖掘每个像素JND阈值与其周围邻近像素JND阈值之间的空间相关性,再利用索贝儿(Sobel)边缘检测算子将TU分成不同类型的图像块,并且计算出对应的复杂度因子,最后结合上述像素JND阈值的空间相关性和TU复杂度因子对TU残差进行滤波。提出的算法模型可以嵌入到高效率视频编码(High Efficiency Video Coding,HEVC)框架。实验结果表明,在全I帧配置下,提出的算法与标准算法HM16.0相比,在人眼主观感知质量基本一致的情况下,平均可节省16.1%的码率。     

一种图像脉冲噪声小波域广义滤波算法

提出了一种脉冲噪声滤波算法.首先对噪声图像进行二维小波分解,得到高频和低频子图像;其次对高频子图像序列采用改进自适应加权中值滤波进行处理,以排除水平、垂直、对角方向的噪声;然后对于低频子图像引入基于修正系数的维纳滤波进行处理,并进行小波系数重构;最后设计出一种小波域图像增强模型,通过设置调节系数,将图像分为不同区域分别进行相应比例的对比度拉伸处理,结合实验定量讨论了噪声强度与模型系数的函数关系.实验表明,该滤波算法不仅优于几类单一滤波算法,相对于某些组合滤波算法而言,也具有一定的优势.     

对数域的光学相干层析图像噪声模型分析

为了分析光学相干层析成像技术(OCT)的图像对数变换前后的斑点噪声分布模型,为图像去噪及其它图像处理过程提供参考,采用了先推导斑点噪声理论分布模型,再通过实验数据验证的方法。首先分析了对数变换前斑点噪声的统计特性,利用数学理论推导得到斑点噪声对数变换后的理论分布模型,然后用OCT心血管图像的平滑区域作为噪声的试验数据,得到变换前后斑点噪声的直方图分布数据,最后用理论分布模型对试验数据进行曲线拟合,取得了确定系数、均方根差和卡方检测的评价数据。结果表明,对数变换后斑点噪声分布符合Fisher-Tippett分布。这一结果对OCT图像去噪等处理过程是有帮助的。     

一种小波域与空域相结合的图像滤波方法

利用小波阈值去噪方法和传统空间域Lee滤波的特点,提出了一种图像去噪的的组合滤波方案。首先在小波域对图像阈值去噪,得到预去噪图像;再在空间域上利用自适应Wiener滤波器进一步提高恢复图像的精度。为了保证小波域和空间域两种算法之间的匹配,对预去噪图像中残留噪声的分布进行了研究,对其噪声方差估计做了改进,提出了一种估计噪声方差的近似最优公式。仿真实验表明,与单独的在小波域或空域去噪相比,该方法的均方误差和信噪比指标均得到了改善。     

Penalized weighted least-squares approach to sinogram noise reduction and image reconstruction for low-dose X-ray computed tomography

Reconstructing low-dose X-ray computed tomography (CT) images is a noise problem. This work investigated a penalized weighted least-squares (PWLS) approach to address this problem in two dimensions, where the WLS considers first- and second-order noise moments and the penalty models signal spatial correlations. Three different implementations were studied for the PWLS minimization. One utilizes a Markov random field (MRF) Gibbs functional to consider spatial correlations among nearby detector bins and projection views in sinogram space and minimizes the PWLS cost function by iterative Gauss-Seidel algorithm. Another employs Karhunen-Loève (KL) transform to de-correlate data signals among nearby views and minimizes the PWLS adaptively to each KL component by analytical calculation, where the spatial correlation among nearby bins is modeled by the same Gibbs functional. The third one models the spatial correlations among image pixels in image domain also by a MRF Gibbs functional and minimizes the PWLS by iterative successive over-relaxation algorithm. In these three implementations, a quadratic functional regularization was chosen for the MRF model. Phantom experiments showed a comparable performance of these three PWLS-based methods in terms of suppressing noise-induced streak artifacts and preserving resolution in the reconstructed images. Computer simulations concurred with the phantom experiments in terms of noise-resolution tradeoff and detectability in low contrast environment. The KL-PWLS implementation may have the advantage in terms of computation for high-resolution dynamic low-dose CT imaging.     

Estimation of the local statistical noise in emission computed tomography

A simple modification of the filtered backprojection algorithm is presented for the computation of the local statistical noise in emission computed tomography. The technique is general in that any distribution of radioactivity may be accommodated. When applied to positron emission tomography, it is shown that the effects of photon absorption, random coincidences, radioactive decay, and detector nonuniformity may be included. Calculations have shown the effects of resolution, object size, and photon absorption on the statistical noise of disk-shaped emitters. Comparison of calculation and experiment show close agreement both in magnitude and spatial variation. Measurements of the noise level in tomograms of the brain obtained during continuous inhalation of 150-CO2 demonstrate that estimates of radioactivity concentration with a precision of a few percent are readily attainable.     

Fast noise reduction in computed tomography for improved 3-D visualization

Computed tomography (CT) has a trend towards higher resolution and higher noise. This development has increased the interest in anisotropic smoothing techniques for CT, which aim to reduce noise while preserving structures of interest. However, existing smoothing techniques are slow, which makes clinical application difficult. Furthermore, the published methods have limitations with respect to preserving small details in CT data. This paper presents a widely applicable speed optimized framework for anisotropic smoothing techniques. A second contribution of this paper is an extension to an existing smoothing technique aimed at better preserving small structures of interest in CT data. Based on second-order image structure, the method first determines an importance map, which indicates potentially relevant structures that should be preserved. Subsequently an anisotropic diffusion process is started. The diffused data is used in most parts of the images, while structures with significant second-order information are preserved. The method is qualitatively evaluated against an anisotropic diffusion method without structure preservation in an observer study to assess the improvement of 3-D visualizations of CT series and quantitatively by determining the reduction of the difference between low and high dose CT scans of in vitro carotid plaques.      

谱域OCT光谱分析及图像噪声消除方法

在谱域OCT系统中,成像过程存在原理性噪声以及系统暗噪声,影响了图像质量,造成图像信噪比降低,图像局部结构信息缺失,因此,对谱域OCT系统的干涉光谱成分和光谱噪声的形成机制进行分析,提出了针对干涉光谱解耦的噪声处理方法.对单层薄膜成像实验,得到了薄膜的二维层析图像,实验结果表明,噪声消除方法对薄膜的成像处理简单有效,能...     

Nonuniform noise propagation by using the ramp filter in fan-beam computed tomography

It is observed that when the homogeneity property of the ramp filter is used to derive a filtered backprojection algorithm in fan-beam tomography, the reconstructed images have nonstationary frequency components and nonstationary noise. When a short focal-length is used, higher frequency components are amplified more at the edge of the image than at the center of the image, resulting in higher noise at the edge of the image.     

Realizations of fast 2-D/3-D image filtering and enhancement

This paper proposes a novel algorithm for multidimensional image enhancement based on a fuzzy domain enhancement method, and an implementation of a recursive and separable low-pass filter. Considering a smoothed image as a fuzzy data set, each pixel in an image is processed independently, using fuzzy domain transformation and enhancement of both the dynamic range and the local gray level variations. The algorithm has the advantages of being fast and adaptive, so it can be used in real-time image processing applications and for multidimensional data with low computational cost. It also has the ability to reduce noise and unwanted background that may affect the visualization quality of two-dimensional (2-D)/three-dimensional (3-D) data. Examples for the applications of the algorithm are given for mammograms, ultrasound 3-D images, and photographic images.     

分数域啁啾滤波及其在数字图像处理中的应用

讨论了分数域啁啾滤波的基本原理,同时将光学中的分数傅里叶变换引入到数字图像处理中,提出了一种分数域滤波去除影响数字图片质量之啁啾噪声的新方法,比较了分数域啁啾滤波和常规傅里叶频谱面上的滤波,获得了满意的模拟结果。     

小波域中的维纳滤波法在星图降噪中的应用

小波阈值降噪法是一种简单而有效的方法．在图像降噪处理中广泛使用。但对于任意信号,在MSE意义上的最优信号估计是Wiener滤波器,在此基础上提出了一种基于小波域上的经验Wiener滤波器的设计方法,并应用在星图降噪中,实验结果表明,此方法比一般小波阈值降噪法的效果好得多。     

A fast novel algorithm for salt and pepper image noise cancellation using cardinal B-splines

This paper discusses a novel algorithm for salt and pepper image noise cancelation using cardinal B-splines. The purpose of this paper is to present an analysis and application of cardinal B-splines for image noise cancellation. To apply the cardinal B-splines, one should analyze the different properties of the cardinal B-spline. Here we make use of the interpolation property and compact support of the cardinal B-splines. There are various assumptions and conditions that are considered while applying the cardinal B-splines for noise removal. The result of denoising the images affected up to 95 % of the salt and pepper noise has been shown. The results of proposed method are being compared with the other existing methods, and the comparison shows the better performance of our method.     

The tradeoff between noise,data rate,and power consumption of transimpedance amplifiers for optical receivers

Analog Integrated Circuits and Signal Processing - The inverter-based shunt-feedback transimpedance amplifier (TIA) has become an essential building block for high-speed receivers for optical...     

Adaptive 3-D median filtering for restoration of an image sequence corrupted by impulse noise

An adaptive 3-D median filtering, which achieves optimal image quality as well as fast computing time, is proposed to remove the impulse noise from a highly corrupted image sequence. The proposed algorithm is compared with the widely used impulse noise removal algorithms with respect to the peak signal-to-noise ratio and the number of computations. The proposed algorithm preserves the image details which are not expected to be corrupted by impulse noise so that the number of computations can be minimized. It has good restoration performance whether the number of pixels corrupted by impulse noise is large or small. In the proposed algorithm, the impulse noise ratio, which is the ratio of the number of pixels corrupted by impulse noise to the total number of pixels, is estimated, and the restoration filtering is adaptively applied based on the estimated impulse noise ratio.     

基于二维DFT域全相位滤波的图像多分辨率分析

图像多分辨率分析在信号滤波、图像除噪、图像 融合、图像边缘检测领域中应用广泛。该文设计了一种新的 图像多分辨率分析方法,通过对全相位系统函数进行谱分解,实现了基于全相位的严格功率 互补的高低通滤波器设计, 按照全相位处理的基本理论,选择不同的正交变换方式和基窗函数可以方便地设计出具有不 同分析/合成效果的全相位波 包。实验表明,DFT域全相位分析滤波器可以实现对图像的多层分解,由合成滤波器还原得 到的图像误差几乎为零。在 图像数据压缩、自适应除噪方面具有较为广泛的应用前景。     

一种基于椒盐噪声新型组合滤波算法仿真研究

提出了一种新型组合滤波算法。该算法首先在噪声方差估计、滤波模板类型和尺寸大小等方面对自适应维纳滤波进行改进,对图像噪声进行预处理;其次将预处理后的图像进行二维多尺度小波分解,由于低频子图像基本不受噪声污染,故不作处理;然后对开关中值滤波分别从噪声检测、噪声分类、噪声滤波等方面进行改进,并给出具体实现步骤,用于小波域高频子图像滤波;最后将滤波后高频子图像和低频子图像进行小波系数重构。实验结果表明,两类改进滤波算法在滤波性能上均优于原始算法,在抗噪性和细节保持等方面具有一定优势。