调制传递函数在遥感图像复原中的应用

针对空间推扫型全色TDICCD 相机在获取、传输和存储图像的过程中引入模糊和噪声导致图像质量下降的问题,提出了一种基于调制传递函数（MTF）的。感图像复原方法。文中的复原方法是通过图像的MTF 恢复出点扩展函数（PSF）,并将其作为退化函数进行图像复原。通过在MTF 提取前对局部图像用同态滤波算法进行增强处理,加强MTF 提取的抗噪声能力,并使用二次复原的方法避免直接加入增强滤波器导致的MTF 误差。使用均值、对比度及边缘强度等指标对。感图像复原结果进行评价。实验结果表明:复原后图像灰度均值提高45%,平均梯度和边缘强度分别是复原前的3.5和1.75 倍,各项评价指标均优于原始图像,并且MTF 所包含面积MTFA 明显增加,该图像复原算法对提高空间TDICCD 相机图像质量有一定的参考意义。     

高分辨率CCD相机传递函数的实时计算

为了获得大数据量、高速图像下传的高分辨率CCD相机的实时传递函数,提出了一种基于图像快视与采集记录系统的CCD相机成像质量自动评价方法。应用计算机高速信息采集和存储技术,在分析对比度传递函数和调制传递函数之间关系的基础上,利用高对比度矩形靶标法计算CCD相机的传递函数,设计了传递函数实时计算系统,从而完成对CCD相机整机系统的像质实时评价。实验结果表明：当像元数达到20 000个,采集速度达到3.2Gb/s时,该方法能够高速率并且准确实时地计算传递函数。     

复小波域HMT模型图像复原

提出了基于二元树复小波变换（DT-CWT）的复小波域隐马尔可夫树（HMT）模型线性图像复原算法,并采用一种简单可行的快速算法来估计HMT模型参数。该方法较好地再现了各种边缘信息,其复原结果较传统的复原方法有不同程度的提高,其运行效率较传统的HMT模型参数估计方法有明显的提高。     

高分辨光学卫星传感器在轨MTF检测

调制传递函数（MTF）是光学卫星传感器像质评价的重要参数,在轨MTF检测关系到高分辨卫星遥感数据的应用和未来卫星遥感器的发展。目前主要有刃边法、脉冲法、点源法、周期靶标法等多种在轨MTF检测方法,这些方法各有特点,均取得一定的在轨检测成效。通过对常用的在轨MTF检测方法的论述,对比分析了不同方法的适用范围、参照目标布设、数据处理及应用效果等,以期提高不同空间分辨率的光学卫星传感器在轨MTF检测精度。     

交替使用小波去噪和全变差正则化的盲图像恢复算法

盲图像恢复就是在点扩散函数未知情况下从降质观测图像恢复出原图像.该文提出了一种交替使用小波去噪和全变差正则化的盲图像恢复算法.观测模型首先被分解成两个相互关联的子模型,这种分解转化盲恢复问题成为图像去噪和图像恢复两个问题,可以交替采用图像去噪和图像恢复算法求解.模糊辨识阶段,使用全变差正则化算法估计点扩散函数;图像恢复阶段,使用小波去噪和全变差正则化相结合的算法恢复图像.实验结果和与其它方法的比较表明该文算法能够获得更好的恢复效果.     

面向卫星动中成像模式的地面实验系统

动中成像模式可实现卫星在大角度快速机动过程中成像,满足遥感观测多样化、定制化、精细化需求。分析了动中成像地面实验系统的基本原理,并在实验室搭建了一套面向动中成像模式的地面实验验证系统。该系统采用高精度、高稳定的动态气浮靶标和基于外触发信号的相机积分时间调整方法。研究了成像质量和光强的关系以及成像质量和相机探测器积分级数、卫星机动角速度的关系,开展了自定义运动曲线的动中成像实验。结果表明,在相机探测器线性区内,不同机动角速度与探测器积分级数获取的图像动态调制传递函数(MTF)值的范围为0.0918~0.1054,满足工程应用(0.1附近)的要求,且MTF值与机动角速度、探测器级数无关。动中成像实验中系统运行稳定,动态MTF值在0.1015±0.0098之间。     

基于小波域改进HMT模型的图像恢复算法

针对图像恢复中的边缘模糊问题,提出了一种基于小波域改进隐马尔可夫树( IHMT) 模型的图像恢复算法。IHMT模型更多描述了相邻尺度小波系数的互相关性,能准确刻画自然图像小波系数的统计特性。本文从图像恢复的贝叶斯框架出发,将简化的IHMT模型作为图像小波域的先验模型,构造正则化约束进行图像恢复。采用近似等价的方法,将含有混合密度的恢复方程简化为单一密度求解。实验结果表明,该算法能有效再现图像的边缘信息,提高峰值信噪比。     

Wavelet-based neural network with fuzzy-logic adaptivity fornuclear image restoration

A novel wavelet-based neural network with fuzzy-logic adaptivity (WNNFA) is proposed for image restoration using a nuclear medicine gamma camera based on the measured system point spread function. The objective is to restore image degradation due to photon scattering and collimator photon penetration with the gamma camera and allow improved quantitative external measurements of radionuclides in vivo. The specific clinical model proposed is the imaging of bremsstrahlung radiation using ³² P and ⁹⁰Y. The theoretical basis for four-channel multiresolution wavelet decomposition of the nuclear image into different subimages is developed with the objective of isolating the signal from noise. A fuzzy rule is generated to train a membership function using least mean squares to obtain an optimal balance between image restoration and the stability of the neural network, while maintaining a linear response for the camera to radioactivity dose. A multichannel modified Hopfield neural network architecture is then proposed for multichannel image restoration using the dominant signal subimages     

基于神经网络和维纳滤波的半盲离焦图像复原

本文提出了一种基于小波神经网络和维纳(Wiener)滤波的半盲离焦图像复原算法,首先提取训练图像的小波域特点参数向量,将该参数用来训练小波神经网络,利用训练好的网络估计图像离焦模糊参数.由离焦模糊参数获得点扩展函数,然后用Wiener滤波完成图像的复原.实验结果表明:该方法能有效地估计离焦模糊参数和复原模糊图像.     

运动模糊图像复原算法的改进及性能研究*

为提高运动模糊图像复原算法的有效性和实时性,分析了常见图像复原算法的优缺点。在此基础上,提出了一种基于小波分解和维纳滤波相结合的图像复原算法。新算法充分利用了小波变换的多分辨率分析特性和维纳滤波复原算法的高效性,既有效抑制了噪声,又减小了图像的灰度失真。仿真结果表明,本文算法不仅提升了图像复原质量,也能满足系统实时性的要求,是一种有效的图像复原算法。     

Robust Noise Estimation Based on Noise Injection

Noise estimation is an important premise for image denoising and many other image processing applications, and related research has drawn increasing attention and interest. In this paper, a novel noise level estimation algorithm is proposed by investigating the distribution of local variances in natural images. There are two major contributions of this work to tackle with the challenges in noise estimation: 1) a wavelet decomposition based preliminary estimation stage to alleviate the influence of image’s textural or structural information; 2) a noise injection based estimation stage to simulate the impact of noise-free image content on the variance distribution, which otherwise almost always leads to overestimation. The cascade scheme of this two-step estimation procedure can reduce the detrimental influence of textural image regions effectively and therefore relieves overestimation of the noise variance. Moreover, the proposed method is not limited to any specific type of noise distribution. Extensive experiments and comparative analysis demonstrate that the proposed algorithm can reliably infer noise levels and has robust performance over a wide range of visual content, as compared to relevant methods.     

单帧振动模糊图像的快速恢复算法

振动退化图像的恢复算法面临的主要问题是在比较宽松的约束条件下对模糊图像的快速恢复。在对国内外的振动模糊图像恢复算法进行充分研究的前提下,提出一种快速有效的算法。首先应用伪白化叠加的方法得到与点扩展函数对应的调制传递函数,然后根据最小相位的理论,解线性方程组得到点扩展函数。在较少的约束条件下避免了传统算法循环迭代计算复杂、费时等缺点,实验结果表明,恢复效果较好,抗噪声能力强。     

高速飞行条件下长曝光图像复原方法北大核心CSCD

在大气层、临界层中高速飞行的飞行器其周边的光学成像环境复杂,准确求解点扩散函数并抑制噪声是图像复原的两个重点。针对目前复原算法存在抗噪性能差、先验信息利用不足等问题,本文提出高速飞行条件下长曝光图像的图像复原方法。首先构造多尺度多方向形态学滤波器对图像进行去噪预处理;引入小波变换将小波的多分辨率特征与图像复原相结合,进一步抑制残留噪声并加快运算速度;采用结合最大类间方差法的Radon变换计算运动模糊点扩散函数;最后构造多直线拟合模型,提出基于图像梯度的对称频谱估计,自适应重建清晰图像频谱。实验表明,本文算法可使用单幅长曝光图像完成有效去噪和去模糊,满足实时复原场景,PSNR和SSIM评价指标数值有效提升。     

深度学习辅助的5G OFDM系统的信道估计

传统的信道估计算法难以满足5G系统中的高速率低时延的需求。针对该问题,将通信信道的时频响应视为二维图像,提出了一种基于图像恢复技术的信道估计方法。首先,设定参数产生基于5G 新空口（ New Radio,NR）标准的物理下行链路共享信道（ Physical Downlink Shared Channel,PDSCH）的信道数据信息数据集,将所产生的信道矩阵看作二维图像;然后,构建基于卷积神经网络的图像恢复网络,并融入残差连接来提高网络的性能;最后,利用训练好的网络模型进行信道估计。仿真结果表明,与最小二乘算法（Least Square,LS）、实际信道估计（Practical Channel Estimation,PCE）和基于图像超分辨率ChannelNet网络相比,所提出的信道估计算法性能提升明显。     

Relative importance of the error sources in Wiener restoration of scintigrams

Through simulation studies, the relative importance of three error sources in Wiener filtering as applied to scintigrams is quantified. The importance of these error sources has been quantified using the percentage changed in squared error (compared to that of an image restored using an ideal Wiener filter) which is caused by estimating one of three factors in the Wiener filter. Estimating the noise power spectrum using the total image count produced to appreciable change in the squared error (less than 1%). Estimating the power spectrum of the true image from that of the degraded image produced small to moderate increases in the squared error (4-139%). In scintigraphic imaging, the modular transfer function (MTF) is dependent on source depth; hence, this study underscores the importance of using methods which reduce the depth dependence of the effective MTF prior to applying restoration filters. A novel method of estimating the power spectrum of the true image from that of the degraded images is also described and evaluated. Wiener restoration filters based on this spectral estimation method are found to be competitive with the image-dependent Metz restoration filter.     

Space-Variant Restoration of Images Degraded by Camera Motion Blur

We examine the problem of restoration from multiple images degraded by camera motion blur. We consider scenes with significant depth variations resulting in space-variant blur. The proposed algorithm can be applied if the camera moves along an arbitrary curve parallel to the image plane, without any rotations. The knowledge of camera trajectory and camera parameters is not necessary. At the input, the user selects a region where depth variations are negligible. The algorithm belongs to the group of variational methods that estimate simultaneously a sharp image and a depth map, based on the minimization of a cost functional. To initialize the minimization, it uses an auxiliary window-based depth estimation algorithm. Feasibility of the algorithm is demonstrated by three experiments with real images.     

偏流角对空间相机影响研究

研究了卫星运行中偏流角对TDICCD相机像质的影响.根据卫星运动状态,推导了偏流角的具体变化形式,以及由其在穿航方向和沿航方向引起的相机像移和由此造成的像质退化调制传递函数(MTF).并针对高度为500km的圆形卫星轨道,定量计算了偏流角导致的像移对相机像质的影响程度.结果表明:偏流角在赤道附近最大,随着纬度的升高,偏流角呈非线性减小.并且,由它引起的像移在穿航方向对相机像质的影响远大于沿航方向.对于给定的轨道参数,偏流角最大值约为3.7°,当积分级数为32时,由其引起的像移调制传递函数接近于零,严重影响了相机的成像质量.为此,提出了使用二维摆镜和调整焦平面方向两种实时补偿偏流角影响的方法.     

Multiple resolution image restoration

A new algorithm for solving the deconvolution problem is proposed. This algorithm uses the wavelet transform to induce a multiresolution approach to deconvolve a blurred signal/image. The low resolution part of a signal/image is restored first and then high resolution information is added successively into the estimation process. Two different ways to incorporate the image space positivity constraint, namely loosely and strictly, are discussed. In to most restoration algorithms, the positivity constraint is applied directly in the transformed domain. The performance of the algorithm in the presence of noise is also investigated     

基于旋转阵列的多帧合成孔径图像复原

针对光学合成孔径成像系统的调制传递函数 (MTF)在中-低频段的衰减以及造成的合成图像降质问题,以6孔径Y型 阵列 为例,提出子孔径阵列旋转成像以获取包含互补信息的多帧图像;通过截止频率与中频能量 比确定旋转角度,并 利用多帧迭代盲解卷积算法进行图像复原。实验表明,与现有的代表性工作相比,本文方法 对于Y型阵列的合成孔径图像有较好的复原效果和重建的准确性。     

相向运动条件下图像的辐射状退化及其复原研究

当摄像机随载体作高速运动时,由于成像曝光时间、摄像机与目标间的纵向相对运动等因素使目标图像产生从中心到边缘的辐射状模糊,使系统有效视场减少,影响对目标的探测、识别和跟踪.本文根据运动成像关系和光电探测器的信号积分机理,研究了摄像平台高速运动条件下,图像辐射状模糊的图像退化模型,对几种特殊图像的退化进行了分析;并针对实际离散成像过程,建立了图像退化模型,分析了影响辐射状退化的因素;提出了一种辐射状模糊图像的递推复原处理算法;计算机方法模拟的辐射状退化图像与实际图像一致,复原算法可有效地减轻相向运动所造成的图像辐射状模糊.