点扩散函数选取对波前编码图像复原影响的实验研究

波前编码系统由于其离焦不敏感和像差抑制特性被广泛应用于光学系统中来延拓景深。景深的拓展是以牺牲图像像质为代价,通过数字复原方法获得正常水平的图像质量。通过对比分析两种复原方式,一种是焦点处的点扩散函数复原全部离焦位置的模糊图像,另一种是点扩散函数分别复原对应离焦位置的模糊图像,通过仿真模拟和显微实验成像对比分析得知点扩散函数复原对应离焦位置的模糊图像的复原方式可以有效削减振铃效应。该复原方式可以减弱图像二次模糊,复原结果更适合人眼观察。     

一种优化波前编码系统相位板参数的新方法

根据波前编码系统的设计理论,在兼顾图像恢复能力的基础上,提出利用不同离焦距离的点扩散函数与焦面处的点扩散函数之间的希尔伯特空间角作为成像特性一致性的评价函数,结合遗传算法,对扩大景深的波前编码成像系统的相位板参数进行优化。分别在空间域和频率域上分析应用波前编码技术前后光学系统的成像特性,并利用最小二乘数字滤波器对中间模糊图像进行复原。仿真实验结果表明:在三次相位板上应用此方法获得的最佳相位板参数使波前编码系统焦深扩展了10倍。     

基于相位差异法的简易光学系统的图像复原方法

简易光学系统因系统结构简单而存在严重像差,导致所成图像出现模糊、失真等问题.对简易光学系统的成像特性进行分析,在已知光学系统焦距和光瞳孔径的条件下,建立含有像差的点扩散函数模型和图像复原模型,根据焦面和离焦面图像以及精确的离焦量,无需点扩散函数的先验信息,采用相位差异法对简易光学系统所成图像进行重构.实验结果表明:单透镜、双透镜和三透镜系统复原图像质量评价指标提升率分别达到24.96%、24.80%和42.04%,重构后图像质量均有明显提升.     

离焦模糊图像的维纳滤波恢复

为消除离焦误差产生的图像模糊,介绍了基于逆滤波和维纳滤波的离焦模糊图像复原方法。从光学成像原理出发,根据高斯方程计算离焦误差,建立离焦误差与光学传递函数之间的关系。讨论了离焦误差对光学成像系统传递函数的影响。通过建立线性空间不变的模糊模型,构建点扩散函数和光学传递函数,采用与模糊过程相反的处理方法进行图像复原,消除离焦误差造成的图像模糊。测试实验中,对标准样本Lena图像进行了离焦模糊处理,采用维纳滤波算法复原图像,选择不同的离焦半径和维纳滤波参数进行对比。实验结果表明:维纳滤波方法可有效消除离焦模糊;抑制噪声干扰和"振铃效应";可把图像峰值信噪比提高到6dB以上。     

基于离焦图像复原的光学设备实时视频对焦方法

针对大口径光学设备使用过程中因传感器靶面离焦导致的图像模糊问题，从图像复原方法入手，推导光学设备的离焦点扩散函数和离焦传递函数，提出图像离焦程度判断方法，运用爬山法、逆滤波方法，寻找最佳离焦量值和方向，复原模糊图像为清晰图像，给出了大口径光学设备的实时视频对焦方法,并进行实验验证。结果表明该方法在外场光学设备的自动调焦中具有重要的推广应用价值。     

基于微分图像自相关的离焦模糊图像盲复原

针对离焦模糊图像的盲复原算法的研究具有重要的实际意义和实用价值.根据光学离焦成像模型,研究提出了一种基于微分图像自相关的离焦模糊图像超分辨力盲复原算法,即首先采用拉普拉斯算子对离焦模糊图像进行二阶微分并求微分图像的自相关,然后从自相关结果所包含的信息中确定离焦模糊半径,最后以离焦模糊模型结合MPMAP超分辨力复原算法对离焦模糊图像进行肓复原.实验证明:算法能够以较高的精度估计出离焦模糊半径并实现离焦模糊图像的盲复原,该算法较其它同类算法在减少计算过程中需要考虑的各类因素的同时也减少了计算量,提高了结果精度,依靠超分辨力复原算法获取更多的复原图像信息,已在实际刑侦和物证鉴定的离焦模糊图像判读和鉴定中获得成功应用.     

基于图像复原的高光谱图像前向像移补偿

为了提高高光谱图像空间维的图像分辨力,针对航空遥感器成像时由前向像移造成的图像模糊提出了像移补偿方法。分析了航空遥感器前向像移造成图像模糊的退化机制,对运动模糊图像进行了预处理;估计了点扩散函数和噪声功率,使用改进的维纳滤波算法对图像进行复原并以绝对平均误差、峰值信噪比作为评价标准进行了实验。在估计出模糊图像点扩散函数和噪声功率的情况下得到的结果显示:与传统的维纳滤波复原算法相比,改进的维纳滤波复原算法的图像绝对平均误差降低了9.31%,峰值信噪比提高了13.98%,表明提出的算法能够有效改善高光谱图像的像质。     

单幅模糊图像点扩散函数估计的梯度倒谱分析方法研究

针对单幅图像复原算法引入先验信息导致复杂度高、运算效率低的问题, 提出了单幅模糊图像点扩散函数估计的梯度倒谱分析方法. 首先给出了单幅模糊图像梯度倒谱估计其点扩散函数的基本原理, 利用相位恢复策略复原了二维点扩散函数相位信息, 实现了点扩散函数的快速估计; 其次, 为鉴别点扩散函数估计精度, 建立了图像梯度保真约束的全变分正则化图像复原模型, 并采用快速稳定收敛的交替方向策略优化能量函数; 通过对仿真和实拍单幅模糊图像进行的测试实验结果表明, 该方法快速准确地估计出点扩散函数, 克服了传统复原算法收敛速度慢的缺点, 有效抑制了振铃效应、保护了边缘信息, 为大尺寸单幅图像复原的工程化实现提供了理论和技术基础. 关键词： 图像复原 点扩散函数 梯度倒谱分析 全变分     

用神经网络鉴别退化图像的模糊类型

提出了一种用神经网络鉴别退化图像的模糊类型的方法。由于采用不同降质方法得到退化图像的频谱差异较大,以此作为判别依据,用概率神经网络实现了对四种模糊类型:离焦,矩形,运动和高斯模糊的鉴别。根据神经网络的鉴别结果决定点扩散函数的初始估计值,可大大地提高盲解恢复算法的复原质量和系统点扩散函数的估计精度,扩大了算法的实用范围。     

应用波前编码技术提高空间相机的稳健性

通常情况下,焦面在光学系统焦深范围内移动,空间相机像质变化较小,一旦移出焦深范围,像质将出现不同程度的下降。波前编码(WFC)成像技术具有很好的扩展焦深功能,能够使光学系统表现出离焦不敏感的特性。采用了扩展多项式在光瞳处引入三次相位分布,以光学传递函数作为系统像质衡量准则构建了自定义评价函数,进行了波前编码光学系统的设计,并搭建了实验装置。实验结果表明,复原后的波前编码图像不仅与原系统成像质量相当,并且在较大的焦深范围内保持一致,验证了波前编码技术提升空间相机稳定性的可行性。     

探测器噪声对波前编码成像系统图像复原过程影响的理论研究

波前编码光学系统其成像过程由光学成像和图像复原两部分组成,光学成像过程探测器上所成的编码图像含有噪声,该噪声在图像复原过程将被放大,为了分析探测器噪声对波前编码系统在图像复原过程中产生的影响,通过添加高斯随机噪声来模拟探测器噪声,使用直接逆滤波、维纳滤波和Lucy—Richardson滤波算法,对波前编码成像系统焦点位...     

Restoration of solar and star images with phase diversity-based blind deconvolution

The images recorded by a ground-based telescope are often degraded by atmospheric turbulence and the aberration of the optical system. Phase diversity-based blind deconvolution is an effective post-processing method that can be used to overcome the turbulence-induced degradation. The method uses an ensemble of short-exposure images obtained imultaneously from multiple cameras to jointly estimate the object and the wavefront distribution on pupil. Based on signal estimation theory and optimization theory, we derive the cost function and solve the large-scale optimization problem using a limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) method. We apply the method to the urbulence degraded images generated with computer, the solar images acquired with the swedish vacuum solar telescope (SVST, 0.475m) in La Paima and the star images collected with 1.2-m telescope in Yunnan Observatory. In order to avoid edge effect in the restoration of the solar images, a modified Hanning apodized window is adopted.The star image till can be estored when the defocus distance is measured inaccurately. The restored results demonstrate that the method is efficient for removing the effect of turbulence and reconstructing the point-like or extended objects.     

多帧距离选通图像点扩散函数估计的超分辨率重建

为了解决水下激光距离选通图像成像过程中退化模型复杂的难题,提出了利用连续帧图像估计点扩散函数的距离选通超分辨成像方法。首先,从连续帧图像中选取一帧为参考帧作为初始清晰图像,下一帧图像为模糊图像,用梯度约束的方法求出点扩散函数,用于优化清晰图像;然后,依次将后续帧图像当作模糊图像与清晰图像交替迭代求取点扩散函数并优化更新清晰图像;最后获得的清晰图像与参考帧图像用乘法更新的方法估计点扩散函数,结合凸集投影法算法进行超分辨率成像重建。仿真实验结果表明,改进的算法重建图像分辨率和质量明显优于原始的算法。     

Point Spread Function Estimation for a Turbulence-Degenerated Image Based on Àtrous Wavelet Transform

The observed object images are seriously blurred because of the influence of atmospheric turbulence. The restoration is required for the reconstruction of turbulence degraded images. Point spread function (PSF) estimation, an essential part of image restoration, has no accurate estimation algorithm at present. Based on the àtrous wavelet, we deduce a novel PSF estimation algorithm. First, the àtrous wavelet at varying scales is transformed. Then, on the basis of the relation among the local maxima of the modulus of the wavelet coefficients at different scales, the Lipschitz exponent of the wavelet coefficients is computed, thus the variance of a PSF is estimated. From this estimated variance, one is able to obtain the PSF. Consequently, the object image can be restored. Experimental results show that the proposed method is highly effective with good performance.     

增量维纳滤波法在波前探测解卷积中的应用

一个常规的自适应光学系统通常包含三个重要环节：波前探测、波前校正和波前重构。因此对系统的技术要求非常高,造成系统复杂,成本昂贵。基于哈特曼-夏克波前探测的图像解卷积处理就是“事后”处理的一种,它省去了波前校正环节,使常规的自适应光学系统得到简化,降低了系统成本。其基本原理为对瞬时波面进行短时间曝光探测,同时记录相应的短时间曝光图像,来进行解卷积处理。将增量维纳滤波法应用于基于哈特曼-夏克波前探测的解卷积中,并对室内模拟点源情况下的三组畸变光斑图像数据进行了解卷积恢复处理。结果表明,将增量维纳滤波法应用于基于波前探测的解卷积是完全可行的,在室内模拟点源情况下,恢复的图像可以达到衍射极限分辨力。与维纳滤波相比,它扩展了噪声抑制因子的选取范围,在噪声抑制因子选取不正确的情况下,仍能得到比维纳滤波更好的结果。     

An apodized cubic phase mask used in a wavefront coding system to extend the depth of field

The point spread function (PSF) caused by a wavefront coding system with a cubic phase mask has big side-lobes which leads to bad image restoration. This paper proposes a novel apodized cubic phase mask to suppress the side-lobes of the PSF. Simulated annealing algorithm is used to optimize the cubic and the truncation parameter of the phase mask. The system with the novel phase mask has better performance in the modulation transfer function (MTF) especially in low-and-medium spatial frequency region. The simulation results show that the restored images with the novel phase mask are superior to the one with the classic cubic phase mask in contrast and ringing effect. The experimental results show that the side-lobes of the PSF are suppressed by using the apodized cubic phase mask.     

Software lens compensation applied to athermalization of infrared imaging systems

A different approach, aiming to achieve the constant blur status of point-spread function (PSF) at a certain defocused plane, is described. The correlation between the two PSF is used to control the PSF blur similarity, and simultaneously the Strehl ratio is also used to control the PSF blur minimization. By designing the PSF so that it is significantly insensitive to defocus or related defocus quantity, for example, due to temperature change, all the constantly blurred images can be accurately de-blurred by a simple inverse restoration filter for an adequate range of defocus. We refer to that as “software lens compensation” and apply a design method to solve the athermalization of middle wavelength infrared (MWIR) imaging systems. The resultant PSF is almost invariant in the temperature range from −10 to 50°C at the same focal plane. Consequently, the constant blur spot can be removed by a simple digital signal processing. Thus, clear and sharp de-blurred images at different temperatures are obtained.     

Restoration of TDI camera images with motion distortion and blur

Platform movement during exposure of imaging system severely degrades image quality. In the case of Time delay and integration (TDI) camera, abnormal movements cause not only image blur but also distortion, for image Point Spread Function (PSF) is space-variant. In this paper, we present a motion degradation model of TDI image, and provide a method to restore such degraded image. While a TDI camera is imaging, it outputs images row by row (or line by line) along the scanning axis, and our method processes in the same track. We firstly calculate the space-invariant PSF of each row using the movement information of the TDI camera. Then, we substitute pixels of the row and the ones of their neighbor rows together with the PSF into standard Richardson–Lucy algorithm. By deconvoluting we get the restored pixels of the row. The same operations are executed for all rows of the degraded TDI image. Finally, a restored image can be reconstructed from those restored rows. Both simulated and experimental results prove the effectiveness of our method.     

Real-time blind deconvolution of retinal images in adaptive optics scanning laser ophthalmoscopy

With the use of adaptive optics (AO), the ocular aberrations can be compensated to get high-resolution image of living human retina. However, the wavefront correction is not perfect due to the wavefront measure error and hardware restrictions. Thus, it is necessary to use a deconvolution algorithm to recover the retinal images. In this paper, a blind deconvolution technique called Incremental Wiener filter is used to restore the adaptive optics confocal scanning laser ophthalmoscope (AOSLO) images. The point-spread function (PSF) measured by wavefront sensor is only used as an initial value of our algorithm. We also realize the Incremental Wiener filter on graphics processing unit (GPU) in real-time. When the image size is 512 × 480 pixels, six iterations of our algorithm only spend about 10 ms. Retinal blood vessels as well as cells in retinal images are restored by our algorithm, and the PSFs are also revised. Retinal images with and without adaptive optics are both restored. The results show that Incremental Wiener filter reduces the noises and improve the image quality.