Image quality of the proton imaging from computer-simulated data

In this paper,the proton image quality of three designed phantoms is studied by the Monte Carlo simulation tool FLUKA,and is compared with that of the photon,and electron imaging.The passages of parallel beams were simulated by the phantoms for protons,electrons and X-rays,and the fluence and energy spectra of exiting particles are recorded.The proton energy loss imaging has a high quality under low transmission proton fluence,and its quality is superior to that of electron and photon fluence.The results demonstrate that proton energy loss imaging is especially suitable for the samples of hundreds of nano-thicknesses.

Image Quality Assessment through FSIM, SSIM, MSE and PSNR—A Comparative Study

Quality is a very important parameter for all objects and their functionalities. In image-based object recognition, image quality is a prime criterion. For authentic image quality evaluation, ground truth is required. But in practice, it is very difficult to find the ground truth. Usually, image quality is being assessed by full reference metrics, like MSE (Mean Square Error) and PSNR (Peak Signal to Noise Ratio). In contrast to MSE and PSNR, recently, two more full reference metrics SSIM (Structured Similarity Indexing Method) and FSIM (Feature Similarity Indexing Method) are developed with a view to compare the structural and feature similarity measures between restored and original objects on the basis of perception. This paper is mainly stressed on comparing different image quality metrics to give a comprehensive view. Experimentation with these metrics using benchmark images is performed through denoising for different noise concentrations. All metrics have given consistent results. However, from representation perspective, SSIM and FSIM are normalized, but MSE and PSNR are not;and from semantic perspective, MSE and PSNR are giving only absolute error;on the other hand, SSIM and PSNR are giving perception and saliency-based error. So, SSIM and FSIM can be treated more understandable than the MSE and PSNR.

Investigation of Noise-Resolution Tradeoff for Digital Radiographic Imaging: A Simulation Study

In digital radiographic systems, a tradeoff exists between image resolution (or blur) and noise characteristics. An imaging system may only be superior in one image quality characteristic while being inferior to another in the other characteristic. In this work, a computer simulation model is presented that is to use mutual-information (MI) metric to examine tradeoff behavior between resolution and noise. MI is used to express the amount of information that an output image contains about an input object. The basic idea is that when the amount of the uncertainty associated with an object before and after imaging is reduced, the difference of the uncertainty is equal to the value of MI. The more the MI value provides, the better the image quality is. The simulation model calculated MI as a function of signal-to-noise ratio and that of resolution for two image contrast levels. Our simulation results demonstrated that MI associated with overall image quality is much more sensitive to noise compared to blur, although tradeoff relationship between noise and blur exists. However, we found that overall image quality is primarily determined by image blur at very low noise levels.

Multi-Modality Medical Image Fusion Based on Wavelet Analysis and Quality Evaluation

Multi-modality medical image fusion has more and more important applications in medical image analysis and understanding. In this paper, we develop and apply a multi-resolution method based on wavelet pyramid to fuse medical images from different modalities such as PET-MRI and CT-MRI. In particular, we evaluate the different fusion results when applying different selection rules and obtain optimum combination of fusion parameters.

星模拟器的光学系统设计研究

基于数字微镜器件(DMD)的工作原理,设计一种工作在0.4~0.7μm波段的星模拟器的光学系统,用于满足星敏感器的性能测试与评估需求。光学系统包括照明系统、棱镜、DMD和投影物镜。照明方式采用科勒照明保证光线均匀照射,其均匀性达到89%。投影系统焦距为87 mm,半视场角为5.75°,出瞳直径为31 mm,出瞳距离为33 mm。该系统经过优化,在37 lp/mm的空间频率下,MTF大于0.7,接近衍射极限,系统畸变小于1%,显示出良好的成像质量。同时,在保证投影光学系统的偏心、倾斜、厚度等公差参数较宽松的情况下,成品率高。总体上,该系统结构紧凑,性能优越,为星空模拟和测试领域带来了重要的参考。

多传感约束下三维运动图像连带动作高质量仿真

因非刚体三维运动图像在成像过程中,传感器区域的随机性对动作限制大、操作复杂,导致动作虚拟精度较低、图像质量差。为此,提出了多传感约束下三维运动图像连带动作高质量仿真。根据多传感器受重力加速度以及地磁场的作用,求解传感器从原始状态到运动当前状态的角度变化。根据变化数值对图像进行去噪,提取连带动作特征。在Vicon系统中计算连带动作空间位置,捕捉连带动作变换轨迹,将运动轨迹结果输入PAR系统,完成连带动作虚拟成像。仿真结果表明:该方法图像去噪效果较好,传感器响应时间始终低于0.52 s,传感器响应速度较快,连带动作轨迹误差始终低于0.045,动作虚拟仿真精度较高,能够有效提高三维运动图像质量。

Scanning transmission proton microscopy tomography of reconstruction cells from simulated data

For scanning transmission proton microscopy tomography,to compare cell images of the proton stopping power and relative electron density,two cell phantoms are designed and simulated by code FLUKA.The cell images are reconstructed by the filtered back projection algorithm,and compared with their tomography imaging.The images of stopping power and relative electron density slightly vary with proton energies,but the internal images are of clear with high resolution.The organic glass image of relative electron density reveals the resolution power of proton tomography.Also,the simulation results reflect effects of the boundary enhancement,the weak artifacts,and the internal structure border extension by multiple scattering.So using proton tomography to analyze internal structure of a cell is a superior.

一种基于散射特征增强的SAR目标电磁仿真图像质量提升方法

现阶段深度学习算法在对合成孔径雷达(Synthetic Aperture Radar,SAR)目标识别时,通常面临着实测数据部分样本缺失的情况,利用电磁仿真数据进行辅助识别是有效途径之一。然而,仿真和实测数据存在不可避免的差异,现有仿真图像质量提升方法更关注仿真和实测图像整体风格的相似性,忽略了面向识别的目标散射特征的重要性。针对上述问题,本文提出了一种基于散射特征增强的SAR目标电磁仿真图像质量提升方法。该方法在循环生成对抗网络(Cycle Generative Adversarial Networks,CycleGAN)框架下,改进损失函数,一方面使用最小二乘损失函数替代交叉熵损失函数,避免了梯度消失,实现对目标纹理结构特征的迭代优化;另一方面引入MS-SSIM-L1损失函数,更好地保留生成图像的细节信息和结构轮廓,保持目标整体结构一致性,同时有效避免模型的过度学习。基于4类车辆目标仿真数据集和MSTAR实测数据集,利用目标轮廓、阴影轮廓和目标强度特征相似度指标,验证了本文方法增强了目标细节纹理和结构轮廓等散射特征。在此基础上,结合A-ConvNets网络开展了目标分类识别实验,相较于原始CycleGAN方法,本文方法在不同样本缺失条件下均提高了识别准确率。通过特征可视化,表明生成图像更接近实测图像的目标特征分布,验证了本文方法的有效性。

基于多旋涡湍流模型的红外退化图像仿真

大气湍流效应会导致红外成像降质,为了有效模拟复杂湍流场引起的红外图像模糊现象,本文综合考虑湍流场中旋涡尺度、强度、数量和旋涡随机偏移等因素,提出一种基于改进类高斯点扩展函数的多旋涡湍流模型,对红外图像进行退化仿真;为了定量评估仿真图像的模糊程度,利用模糊图像中心像素向周围扩散的特点,提出基于相邻像素-锐度的图像降质模糊度评估方法。实验结果表明:所提出的退化模型具有图像质量变化平稳、模型参数细致、仿真可控性强等特点,并且所提出的评估方法能准确地反映图像的降质模糊度。

Super-resolution image restoration algorithm based on orthogonal discrete wavelet transform

By using orthogonal discrete wavelet transform (ODWT) and generalized cross validation (GCV), and combining with Luck-Richardson algorithm based on Poisson-Markov model (MPML), several new superresolution image restoration algorithms are proposed. According to simulation experiments for practical images, all the proposed algorithms could retain image details better than MPML, and be more suitable to low signal-to-noise ratio (SNR) images. The single operation wavelet MPML (SW-MPML) algorithm and MPML algorithm based on single operation wavelet transform (MPML-SW) avoid the iterative operation of self-adaptive parameter in MPML particularly, and improve operating speed and precision. They are instantaneous to super-resolution image restoration process and have extensive application foreground.

Modified Multi-Resolution Telescopic Search Algorithm for Block-Matching Motion Estimation

This paper presents a modified multi-resolution telescopic search algorithm (MRTlcSA) for the block-matching motion estimation. A novel inverse telescopic search is substituted for the conventional telescopic search, that reduces the on-chip memory size and memory bandwidth for VLSI implementation. In addition, strategies of motion track and adaptive search window are applied to reduce the computational complexity of motion estimation. Simulation results show that, compared with the MRTleSA, the proposed algorithm reduces the computational load to only 30% while preserving almost the same image quality. Comparisons on hardware cost and power consumption of the VLSI implementations using the two algorithms are also presented in the paper.

SAR图像组合降斑算法

SAR图像存在较强的相干斑点噪声 ,严重的影响了地物信息的提取与SAR图像的应用效果 ,作者在研究分析斑点噪声产生机理以及统计特性的基础上 ,提出了一种组合降斑重构算法 ,该算法与降斑重构性能优异的模拟退火算法降斑重构性能相当 ,但极大的减少了计算代价 ;与许多其它SAR降斑算法相比 ,组合降斑重构算法具有很好的降斑以及场景结构保持性能 。

卫星姿态指向抖动与SAR成像质量关系研究

建立了卫星姿态指向抖动的数学模型 ,基于成对回波畸变理论推导了存在姿态指向抖动时点目标扩展函数的解析表达式 ,提出了卫星姿态指向抖动幅度与星载SAR(合成孔径雷达 )成像质量关系的定量分析方法 ,为SAR卫星总体分析与设计提供了理论依据 .计算机仿真结果验证了结论的正确性 .

PHILIPS大孔径CT模拟定位机影像质量控制方法研究

目的通过对CT模拟定位机质量控制模体的测试,对CT模拟定位机的各项指标进行质量控制,分析影响图像质量的因素,保证图像质量。方法利用PHILIPS大孔径CT模拟定位机分别对Catphan504模体四大部分进行头部标准质量控制方案轴向扫描,测试其层厚、CT值线性、均匀性、噪声、空间分辨率、密度分辨率。层厚测试扫描条件为120 kV,280 mAs,层厚9.0、6.0、3.0、1.5 mm,旋转时间0.75 s,算法采用EB;CT值线性扫描条件为120 kV,280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB、B;均匀性、噪声、空间分辨率扫描条件均为120 kV,280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB;密度分辨率扫描条件为120 kV,220 mAs、240 mAs、260 mAs、280 mAs,层厚9.0 mm,旋转时间0.75 s,算法EB。结果 9.0 mm、6.0 mm、3.0 mm、1.5 mm标称层厚的测试结果分别为8.82 mm、5.80 mm、2.95 mm、1.55 mm;对于CT值线性,EB、B两种算法的对比度标度分别为1.79×10^(-4) cmHu^(-1)、1.93×10^(-4) cmHu^(-1);均匀性为3.9 Hu;噪声水平为0.34%;空间分辨率为6 LP/cm;220 mAs、240 mAs、260 mAs、280 mAs条件下,密度分辨率分别为4 mm@1%、3 mm@1%、2 mm@1%、2 mm@1%。CT值线性在EB算法条件下,对比度标度近似等于参考值下限值,密度分辨率在220 mAs、240 mAs条件下,其测量值低于参考值,其他测试项目结果均符合要求。结论通过对各项目的检测可保证影像质量最优化,进而保证精确放射治疗的实施。

应用低频信号提高高速玄武岩屏蔽层下的成像质量

针对江陵凹陷陵北玄武岩高速屏蔽层下深层成像困难的实际问题,本文首先分析了玄武岩地层的特点及其对波场传播规律的影响,设计了两个相应的理论模型;采用波动方程波场数值模拟技术,通过对深层反射地震信号特征的分析,表明低频地震信号既具有较强的穿透薄高速玄武岩屏蔽层的能力,也具有减弱粗糙表面产生的绕射噪声的能力。将此思路应用于实际资料处理,结果表明利用低频信号可以明显削弱玄武岩高速屏蔽层的影响,提高屏蔽层下深层成像的质量。

闪光照相系统的散射分布与降散射的数值模拟

对法国试验客体(FTO)的3m照相系统建模,利用MonteCarlo方法模拟X光子输运过程,得到了系统的散射分布和系统器件对散射的贡献。结果表明后保护锥是系统散射的主要来源,对于任意一点,后保护锥的散射占总散射的75%以上。FTO的散射主要是FTO外层材料和边缘的散射,这部分散射占客体总散射的90%以上。利用坡度准直器对系统散射严重的区域进行的降散射,表明坡度准直器是一个很好的降散射器件,能有效提高图像质量。

太阳同步椭圆轨道偏流角分布规律与像质分析

提出一种根据轨道根数与TDICCD成像原理模拟遥感器推扫成像过程,实现偏流角计算,并基于最终仿真图像的PSF分布评价图像质量的方法,以截止频率MTF为评价标准,研究太阳同步椭圆轨道的偏流角分布规律。结果表明:与常规圆轨道相比,近地点幅角为0°的椭圆轨道在近地点一侧偏流角与轨道半长轴成线性关系,与轨道离心率成三次函数关系。使用KH-12卫星采用的椭圆轨道参数进行成像仿真,以穿航MTF下降5%为约束对成像质量进行分析,结果表明:相同推扫级次下,椭圆轨道近地点一侧的偏流角更小,成像质量更高。

星载TDICCD相机像移对成像质量的影响分析

通过分析给出了偏流角变化、速高比变化和姿态精度导致的像移量及其与调制传递函数的对应关系,结合卫星轨道和相机参数,在不同积分级数下引起的像移对相机成像质量的影响进行了仿真。结果表明,随着积分级数的增加,像移对相机成像质量的影响越来越大,尤其表现为偏流角及速高比的变化。为此,在轨运行期间须对其采取补偿措施,为保证高质量的图像,卫星平台必须具有高精度、高稳定度的姿态控制系统。

星模拟器光学系统的设计

星模拟器是星敏感器的地面测试设备。由星敏感器的光学系统要求,确定星模拟器的光学系统的技术参数,通过分析,选择远摄型物镜光学结构,为进一步减小二级光谱,把正光组由原来的正负双分离,再加入一胶合面,后组由正负双分离透镜组成负透镜组,经像质平衡,使全谱段最大平行角度误差≤10"。

卫星平台运动对高分辨率光学遥感成像系统影响分析

在高分辨率光学遥感成像过程中,卫星平台的不稳定性将影响相机成像质量。针对该问题,在分析动态降质机理的基础上分别就面阵凝视模式、线阵推扫模式及时间延迟积分(Time Delay and Integration,TDI)推扫模式提出了相应的动态成像仿真模型,以此模拟不同情况下的退化结果。以高分辨率遥感相机为对象,开展多种情况下的仿真试验分析。结果表明,同等平台运动条件下,TDI推扫模式下的图像质量下降更明显;分辨率越高,像质对平台振动的响应灵敏度越高。最后结合仿真模型及图像评价参量,建立起空间分辨率与平台颤振指标之间的关系,给出不同空间分辨率下的平台运动误差阈值,为平台振动抑制和补偿提供约束条件。