Three-dimensional integral imaging with improved visualization using subpixel optical ray sensing

In this Letter, we propose an improved three-dimensional (3D) image reconstruction method for integral imaging. We use subpixel sensing of the optical rays of the 3D scene projected onto the image sensor. When reconstructing the 3D image, we use a calculated minimum subpixel distance for each sensor pixel instead of the average pixel value of integrated pixels from elemental images. The minimum subpixel distance is defined by measuring the distance between the center of the sensor pixel and the physical position of the imaging lens point spread function onto the sensor, which is projected from each reconstruction point for all elemental images. To show the usefulness of the proposed method, preliminary 3D imaging experiments are presented. Experimental results reveal that the proposed method may improve 3D imaging visualization because of the superior sensing and reconstruction of optical ray direction and intensity information for 3D objects.     

亚像元动态成像技术中系统调制传递函数的数值分析

亚像元动态成像技术是目前实现遥感器小型化非常有效的新方法,因而研究亚像元动态成像系统的调制传递函数MTF显得非常必要和重要.介绍了亚像元动态成像的基本原理及成像过程,指出了光程差对亚像元动态成像系统MTF的影响.对亚像元动态成像系统的MTF进行了数值分析,并指出了亚像元动态成像系统的成像质量及空间分辨率与一般成像系统相比较的优点.     

亚像元动态成像技术中系统的调制传递函数

亚像元动态成像技术是国际上目前实现遥感器小型化非常有效的新方法，因而研究亚像元动态成像系统的调制传递函数（MTF）显得非常必要和重要。本文分析亚像元动态成像系统的MTF模型，并给出亚像元动态成像系统MTF的数学表达式。     

3D image reconstruction with a controllable overlapping number of elemental images in computational integral imaging

In this Letter, we propose a three-dimensional(3D) image reconstruction method with a controllable overlapping number of elemental images in computational integral imaging. The proposed method can control the overlapping number of pixels coming from the elemental images by using the subpixel distance based on ray optics between a 3D object and an image sensor. The use of a controllable overlapping number enables us to provide an improved 3D image visualization by controlling the inter-pixel interference within the reconstructed pixels.To find the optimal overlapping number, we simulate the pickup and reconstruction processes and utilize the numerical reconstruction results using a peak signal-to-noise ratio(PSNR) metric. To demonstrate the feasibility of our work in optical experiments, we carry out the preliminary experiments and present the results.     

目标图像结构和噪声对相关哈特曼-夏克波前传感精度的影响

以空间频谱描述图像结构,以图像灰度起伏的方均根值与噪声方均根值之比表示信噪比,系统分析了目标图像结构和噪声对相关哈特曼-夏克波前传感精度的影响。理论分析表明,两个子图像的相关函数峰值位置的亚像元插值误差等于其各离散频率成分的相关函数峰值位置插值误差的加权平均;相同功率下,低频成分的加权系数较小,高频成分的加权系数与亚像元偏移量有关。一维窄带图像的统计仿真表明,无噪声时,低频成分和接近奈奎斯特频率成分的误差较大,中频成分的误差较小;有噪声时,噪声对高频成分的影响低于低频成分。对典型频谱的32×32图像仿真表明,图像起伏信噪比为2∶1时,子图像平移量计算误差约0.03~0.11像元,与无噪声时相比增加不大。     

梯度算子选择对基于梯度的亚像素位移算法的影响

基于梯度的亚像素位移算法中不同的灰度梯度计算方法对计算结果的影响进行了研究,列出了几种常用灰度梯度计算方法,并用对相邻5像素点的离散灰度进行三次样条插值的方法推导出两种灰度梯度算子。然后对计算机模拟生成的散斑图像对用各种梯度算子计算得出的亚像素位移与预先设定的真实值做了比较,给出了相应的均值误差和均值相对误差。最后的真实试件的刚体平移和单向拉伸实验结果表明,Barron算子是所列的几种梯度算法中最为精确、稳定的梯度算子。     

高速TDI CCD亚像元动态成像系统分析

亚像元动态成像技术是目前实现相机小型化及提高相机空间分辨率的有效方法。将亚像元动态成像技术引入高速TDICCD相机中,通过特殊设计的光学拼接方法,使相机在不影响扫描速度及不改变TDICCD器件尺寸和相机焦距的情况下,可大大提高空间分辨率。为评价该TDICCD亚像元动态成像系统的成像质量,对成像系统的调制传递函数(MTF)进行了分析,分析结果表明该TDICCD亚像元动态成像技术可以将系统的空间分辨率提高1.6倍以上。     

基于Zernike矩的亚像素边缘定位算法

亚像素软件处理技术可以在一定程度上补偿图像测量系统由硬件限制引起的边缘定位精度,提出了一种基于Zernike矩的亚像素边缘定位算法。该算法利用Zernike多项式的正交性与完备性以及复数矩幅度的旋转不变性计算出边缘的亚像素位置。计算出了像素为正方形与矩形(长宽比为4∶3)时的矩模板,使其应用范围进一步扩大。分析了由于矩模板产生的原理偏差,并提出了修正公式,使定位精度得到提高。进一步推导出了实际边缘模型的定位公式,导出了其存在的偏差,并进行了补偿。最终的实验结果表明,补偿后的算法对直线的定位精度达0.05像素,对曲线的定位精度可达0.07像素。     

基于B样条插值算法的亚像元技术的研究

亚像元动态成像技术是目前实现卫星相机小型化及提高相机空间分辨率的一种有效方法。在不改变TDICCD相机的焦距、成像距离,以及TDI CCD器件的像元尺寸的前提下,亚像元动态成像技术可以提高相机的空间分辨率。利用B样条插值算法,研究了TDI CCD相机的图像的亚像元动态插值问题,由两幅相机输出的原始图像经过算法得到比原图像分辨率高的图像,并对比了该算法与其它几种算法的效果,分析结果表明,该算法较其它算法得到的高分辨率图像的效果更佳。     

亚象元动态成象系统空间分辨率研究

本文从采样间隔和调制传递函数两个方面分析了亚象元成象系统的理论空间分辨率.并将其与实际结果进行了比较.     

亚像元线阵CCD推扫成像系统调制传递函数分析方法

通过对CCD器件成像过程的描述 ,分析亚像元成像系统工作方式 ,从几何参数的角度研究亚像元系统特点 ,及其调制传递函数的分析方法 ,并从理论上进行模拟计算。     

Enhancements in full‐field PIXE imaging—Large area elemental mapping with increased lateral resolution devoid of optics artefacts

The combination of a pn‐junction charge‐coupled device‐based pixel detector with a poly‐capillary X‐ray optics was installed and examined at the Helmholtz‐Zentrum Dresden‐Rossendorf. The set‐up is intended for particle‐induced X‐ray emission imaging to survey the trace elemental composition of flat/polished geological samples. In the standard configuration, a straight X‐ray optics (20 μm capillary diameter) is used to guide the emitted photons from the sample towards the detector with nearly 70 000 pixels. Their dimensions of 48 × 48 μm² are the main limitation of the lateral resolution. This limitation can be bypassed by applying a dedicated subpixel algorithm to recalculate the footprint of the photon's electron cloud in the detector. The lateral resolution is then mainly determined by the capillary's diameter. Nevertheless, images are still superimposed by the X‐ray optics pattern. The optics' capillaries are grouped in hexagonal bundles resulting in a reduced transmission of X‐rays in the boundary regions. This influence can be largely suppressed by combining a series of short measurements at slightly shifted positions using a precision stage and correcting the image data for this shifting. The use of a subpixel grid for the image reconstruction allows a further increase of the spatial resolution. This approach of image‐stacking and multiframe super‐resolution in combination with the subpixel correction algorithm is presented and illustrated with experimental data. Additionally, a flat‐field correction is shown to remove the remaining imaging inhomogeneity caused by non‐uniform X‐ray transmission. The described techniques can be used for all X‐ray spectrometry methods using an X‐ray camera to obtain high‐quality elemental images.     

基于Si-PM阵列的辐射作用位置定位方法研究

在辐射成像中准确估计射线与探测器相互作用的空间位置是保障成像质量的关键步骤。为进一步提升辐射作用事件的定位效果,有效抑制重心法在辐射事件作用位置靠近探测器边缘时造成的定位偏移,针对Si-PM阵列构成的位置灵敏探测系统建立了基于响应函数的定位算法。搭建了基于CsI阵列与Si-PM阵列构成的位置灵敏探测器和基于ASIC的电子学读出系统,使用等效电阻网络简化了Si-PM阵列的输出信号数量, 通过实验获得了辐射事件在Si-PM阵列上的响应函数。实验结果表明,在同一条件下使用响应函数法在最边缘像素散点的FWHM仅为使用重心法获得FWHM的46.2%,与中央像素散点的FWHM相当,基于响应函数的辐射事件方法定位效果明显优于传统重心法的定位效果,可有效克服重心法的边缘效应。     

Adaptive optics retinal image registration from scale-invariant feature transform

With the use of adaptive optics(AO), high-resolution microscopic imaging of the living human retina in the single cell level has been achieved. In an AO retinal imaging system, with a small field size (about 1°, 300 μm) the motion of the eye severely affects the stabilization of the real-time video images results in significant distortions of the retina images. Scale-invariant feature transform (SIFT) algorithm is applied to automatically abstract corner points with subpixel resolution and match the points in two frames. With the matched corner points, we estimate and remove the motions of 20 frames of photoreceptor cells and capillary blood vessels, respectively. The maximal translational motion is about 30 and 44 pixels in the 20 frames whose size is 416 × 416 pixels. More general motions can be considered by the SIFT algorithm, but only simple translational motion can be considered by cross-correlation algorithm.     

混合像元光谱特征影响因子分析

高光谱遥感能够提高地物识别和分类,通过光谱比较和匹配达到分类识别目的。由于传感器空间分辨率以及地面复杂多样性的差异, 混合像元在遥感图像中普遍存在。混合像元的分解问题是定量遥感应用中的一个突出问题, 如何有效地解译混合像元是遥感应用的关键问题之一。研究了面积比始终为1∶1的两种材料形成的混合像元在不同入射天顶角和不同拓扑位置分布时的高光谱反射比曲线的特征与差异,为混合像元分类精度的提高提供科学依据。     

基于OLED微显示器和变形目镜的全景显示技术

全景成像在特种车辆内夜间驾驶与观察、警戒监视等应用中具有广泛的应用需求。本文提出了一种基于OLED微显示器和变形目镜的全景图像显示方法,并设计了一套全景显示实验系统,通过图像处理模块完成全景图像数据的存储、缓存、图像预处理和传输,以OLED微显示器的子像素作为显示像素进行驱动信号重编码,实现全景灰度图像的水平3倍压缩显示,最后利用变形目镜将OLED微显示器上显示的压缩图像复原,以供人眼正常观察。实验结果表明:采用现有系统搭建的变形目镜基本实现了双像素靶标条纹的亚像素分辨,并验证了本文全景显示方案的可行性。     

基于亚像素区域加权能量特征的多尺度图像融合算法

对矩形和圆形区域中各像素进行亚像素划分,确定各亚像素的权值,得到基于哑像素的综合加权区域能量.融合箅法首先对源图像进行金字塔分解,然后对金字塔的高频细节分量使用基于哑像素加权区域能量特征的融合规则取大,对低频粗糙分量取平均.得到融合图像的塔形分解,最后重构融合图像.仿真结果表明,新算法融合效果较常规的区域能量特征作为融合规则的多分辨率图像融合算法效果更好,从清晰度和熵的评价来看,提高了融合图像的品质.     

Prism-Based Spectral Imaging of Single-Molecule Fluorescence from Gold-Nanoparticle/Fluorophore Complex

A wavelength-calibration method for prism-based spectral imaging of single-molecule (SM) fluorescence was developed. With this method, a wavelength reference is provided by photoluminescence from 50-nm-diameter gold nanoparticles (AuNPs) binding with fluorophores. The AuNPs each bound with a SM fluorophore, either Alexa488 or Cy3, to form AuNP/fluorophore complexes in tris-HCl buffer. Each complex was immobilized on a silica slide and then excited by total-internal-reflection illumination to make it emit SM fluorescence and AuNP photoluminescence. The portion of the AuNP photoluminescence transmitted by a band-pass filter gives the wavelength reference. A spectral-imaging system composed of a prism-based spectroscope (with a reciprocal dispersion of about 4 nm/μm) and a charge-coupled device with 6.45-μm-square pixels was used to obtain an SM-fluorescence spectrum and a wavelength-reference spectrum. Through smoothed differentiation of these two spectra, the peak location of the former in relation to the latter was determined with subpixel precision. After that, the SM fluorophore was classified as either Alexa488 or Cy3 according to the peak location. The error rate of the classification was estimated to be only 0.3%.     

亚像元成像系统细胞神经网络插值方法研究

亚像元动态成像技术是实现卫星相机小型化及提高相机空间分辨率的有效方法。采用细胞神经网络(CNN)实现了对亚像元图像的实时插值,对插值的过程进行了详细的分析,并与基于亚像元图像的传统插值方法进行了对比。结果表明,亚像元成像系统细胞神经网络插值方法不仅可以节约系统资源,而且还可以提高系统的运行速度。通过仿真证明了该方法的正确性。     

Luminance adaptation model for increasing the dynamic range of an imaging system based on a CCD camera

We propose a luminance adaptation model (LAM) to increase the dynamic range of an imaging system when scenes containing areas of low and high illumination are imaged. The LAM that we developed is based on capturing images at different exposure times to obtain digital levels within the linear response zone for all the pixels in the image. The levels are subsequently transformed to a reference exposure time that is common to all pixels. We use a linear transformation whose coefficients are determined by the digital levels obtained for a set of flat-spectrum samples. In this study, the LAM is applied to a multispectral imaging system that is based on a CCD camera used for color measurements and spectral reconstructions. It is shown to be a very useful method for increasing the dynamic range of the system, whilst maintaining its accuracy.