基于Sigmoid函数拟合的多曝光图像直接融合算法

同一场景不同曝光的图像序列,常出现曝光不足或曝光过度的区域,造成高亮或阴暗处的细节损失。针对这一问题,提出了基于Sigmoid函数拟合的多曝光图像直接融合算法。该算法从同一场景不同曝光的LDR图像序列中提取每个像素位置亮度信息,利用视觉适应的S形曲线,建立亮度序列曲线的数学模型,给出像素最佳成像亮度值判别方法,避免了HDR图像重建和色调映射的复杂计算,快速合成直接在常规设备上显示的HDR图像。实验结果表明,该方法具有更高的计算效率,极大程度地保留了图像细节,并对运动目标和相机微小移动的影响具有良好的鲁棒性。     

推扫式遥感相机超满阱大动态范围成像

为了提高推扫式遥感相机的动态范围,对应用DTDI(Digital domain Time Delay Integration)技术并采用固定积分级数的成像方法以及高动态范围图像的显示方法等进行研究。首先介绍了DTDI技术基本原理,然后利用该技术突破传统模拟域TDI的满阱电荷限制,获得更高深度、更大动态范围的灰度图像数据,进而拓展了推扫式遥感相机的动态范围。最后结合图像熵和图像灰度分布方差构造评价函数,并将其作为判据选择被关注目标高动态范围图像的最优显示窗口,将信息量最大、层次最为丰富的区间自动显示出来。计算和实验结果表明,当固定积分级数为64的时候,推扫式遥感相机的动态范围可以有效地提高36.124dB;基于评价函数的显示窗口自动选取方法较人工选择能够更加快速、准确地显示最优结果。本文提出的方法能够基本满足推扫式遥感相机领域大动态范围成像及选择显示的需求。     

基于混合映射的高动态范围场景再现

高动态范围场景再现技术广泛应用于消费电子、虚拟现实、摄影以及计算机视觉等领域。针对目前大多数高动态范围场景再现方法很难有效兼顾场景的整体效果和局部细节的问题,本文提出了基于混合映射的高动态范围场景再现方法。首先将输入的高动态范围场景从RGB颜色空间转换到HSV颜色空间,得到原始图像的3个分量:色调、饱和度和亮度;然后利用对数方程将亮度分量转换到对数域,以便符合人类对场景亮度的感知机理,并利用具有sigmoidal函数特性的反正切函数自适应地压缩全局动态范围,以得到良好的整体效果;接着采用改进的SSR方法对全局压缩后的亮度图像进行局部映射,以增强图像亮区和暗区的细节信息;最后,对饱和度分量进行自适应调整,并将图像由HSV颜色空间转换到RGB颜色空间得到最终的映射图像。选取10组不同的高动态范围场景,从主观和客观两方面进行比较分析。实验结果表明:本文提出的方法既保持了良好的整体效果,又充分保留了图像的局部细节,使图像看起来更加生动自然;同时该方法计算速度快,具有很高的效率。本文算法优于其他5种典型的比较算法,在大多数高动态范围场景再现过程中取得了令人满意的效果。     

动态范围对手机拍照质量的影响

动态范围是评估手机拍照质量的一项重要指标。根据手机动态测试的方法及ISO 14524标准建议的透射式测试图卡,建立基于光电转换函数(opto-electronic conversion function,OECF)成像测试系统模型,确定其测试要求,同时对不同手机拍照的动态范围进行分析,明确动态范围的差异对手机拍照能力的影响,为研发人员调整手机拍照功能提供参考。     

用于强反射表面形貌测量的投影栅相位法

为了实现强反射表面三维形貌的光学非接触测量,提出一种改进的投影栅相位法。分析了强反射表面的反射光特点及其对相位解算的影响,指出了反射光亮度范围与相机动态范围的不一致是导致传统投影栅相位法测量失效的主要原因;提出了亮暗条纹投射、多曝光时间采集图像和图像合成等技术,使相机亮度测量范围与强反射表面的反射光亮度范围相一致,并分析了此方法的可行性和适应范围。最后,给出了改进投影栅相位法的条纹投射与图像采集步骤。实验结果表明,改进的投影栅相位法克服了强反射表面引起的条纹图像饱和或过暗问题,能够成功测量出99.6%以上的三维点云,有效解决了测量点云缺失问题,能够实现强反射表面三维形貌光学非接触测量。     

Omnifocus video camera

The omnifocus video camera takes videos, in which objects at different distances are all in focus in a single video display. The omnifocus video camera consists of an array of color video cameras combined with a unique distance mapping camera called the Divcam. The color video cameras are all aimed at the same scene, but each is focused at a different distance. The Divcam provides real-time distance information for every pixel in the scene. A pixel selection utility uses the distance information to select individual pixels from the multiple video outputs focused at different distances, in order to generate the final single video display that is everywhere in focus. This paper presents principle of operation, design consideration, detailed construction, and over all performance of the omnifocus video camera. The major emphasis of the paper is the proof of concept, but the prototype has been developed enough to demonstrate the superiority of this video camera over a conventional video camera. The resolution of the prototype is high, capturing even fine details such as fingerprints in the image. Just as the movie camera was a significant advance over the still camera, the omnifocus video camera represents a significant advance over all-focus cameras for still images.     

振动轮式微机械陀螺动态特性光学测试方法研究

振动轮式微机械陀螺尺寸小、振动频率高,为了精确评价其动态特性,建立了基于高速摄像技术、显微技术与数字图像相关技术的光学测试系统。配有光学显微镜的高速摄像设备(32000fps)记录并保存被测物瞬时序列图像,根据被测物的角振动特性设计相应的图像相关计算方法以获得振子各时刻的运动位移,并通过位移时间曲线分析振子的固有频率、阻尼系数及品质因子等动态特性参数。实验结果显示,图像相关精度达0.01像素,频率测量误差小于0.01%。高精度地测量了振动轮式微机械陀螺的动态特性,为微结构动态特性的研究提供了一个有效方法。     

基于同名点间距变换的三维显示参数匹配

传统集成成像系统以重构场景为记录场景的镜像,而当用相机阵列代替透镜阵列获取元素图像时,两种阵列参数的不匹配会破坏上述镜像关系.为了得到相机阵列获取的元素图像经透镜阵列重构后的物像关系,本文提出用同名点间距计算集成成像重构像距的方法.该方法通过获取端场景物距、相机焦距等参数,得到同名点间距,并等效至重构端透镜阵列系统来实现光学参数的匹配.理论计算表明,同名点间距不同,得到的重构像距也不同.对与透镜阵列参数匹配的同名点间距进行变换处理,即可精确再现不同重构像距的景物.最后,通过实验验证了本文所提方法的有效性.     

Image enhancement for increased dot-counting efficiency in FISH

Background: The most commonly used molecular cytogenetic technique is fluorescence in situ hybridization (FISH). It has been widely applied in many areas of diagnosis and research, including pre‐natal and post‐natal screening of chromosomal aberrations, pre‐implantation genetic diagnosis, cancer cytogenetics, gene mapping, molecular pathology and developmental molecular biology. The analysis of FISH images consists of detecting fluorescent dots, after which the number of dots per cell can be counted or their relative positions can be measured. A major impediment in the analysis of FISH specimens is signal (dot) quality, which is influenced by the hybridization efficiency and/or the sensitivity of the camera that records the images. Method: In this paper, we present an approach to improve the efficiency of detecting fluorescent signals in FISH images by recovering the radiance map of the camera. This allows us to generate a high‐dynamic‐range image wherein an extended range of the sample radiance captured by the camera can be visualized at distinct intensity values. The resulting higher‐order numeric complexity of the transformed image is adjusted (or simplified) by examining the intensity distribution in each of the three colour channels (red, green and blue), and remapping the intensity values to generate a high‐contrast image with a lower‐order (compressed) dynamic range. The remapping is based on a criterion that optimizes the detection of the hybridized signals, allowing attenuation of saturated intensity values while amplifying low‐intensity signals. Results: A simple dot‐counting algorithm is used to automatically process 2000 FISH images. The images are taken for lymphocytes from cultured blood specimens for cytogenetic testing. Images are manually analyzed by an expert to obtain ground truth for dot counts. A quantitative analysis is performed by comparing results of automated dot detection on images before and after enhancement with the developed algorithms. In addition, common errors in dot counting due to split dots, dust, poor segmentation and overlapping signals are analyzed and the robustness of the developed approach against these errors evaluated. It is observed that dot‐detection efficiency is increased by an average of 9% across all colour channels while reducing errors in missed and false dot counts. Conclusions: Our proposed method and results demonstrate that dot‐counting specificity and sensitivity can be improved by pre‐processing and enhancing the image using the radiance curve of the camera and generating a high‐contrast, remapped high‐dynamic‐range image prior to using any algorithm for dot counting.     

细节保留的多曝光图像融合

针对传统的多曝光图像融合算法存在的细节丟失严重和鬼影现象,提出了一种细节保留的多曝光图像融合算法。该算法首先计算曝光序列的3个特征指标:图像细节、曝光亮度和色彩信息,其中图像细节通过引导滤波计算,曝光亮度的权值由高斯方程分配,而曝光序列的色彩信息用色彩饱和度表示。然后,利用差分图和邻域相关系数检测多曝光序列中运动物体,利用3个特征指标和运动目标检测结果分别计算静态场景和动态场景的融合权值图。为了消除噪声的影响,采用递归滤波器来修正融合权值图。最后,采取加权融合的方式得到融合图像。选取10组不同的曝光序列,分别从主观和客观两方面与6种传统的融合算法进行了比较。实验结果表明,本文算法保留了丰富的细节信息,呈现出了更加生动自然的现实场景,并且有效去除了由运动物体产生的鬼影现象,效果优于其他比较算法,在静态场景和动态场景的曝光融合中都取得了好的效果。     

Dark pixel intensity determination and its applications in normalizing different exposure time and autofluorescence removal

The purpose of this study is to investigate how to scale pixel intensity acquired from one exposure time to another. This is required when comparing grayscale images acquired at different exposure times and other image processing such as autofluorescence removal. Pixel intensity is linear to exposure time as long as images are acquired at the linear range of a camera, but importantly there exists an intercept, which is set by the camera. We termed this intercept as dark pixel intensity, as it is the pixel intensity under conditions of no light and zero exposure time. Dark pixel intensity is determined by camera's readout noise (electron/pixel), gain, and DC offset. Knowing dark pixel intensity, image acquired from one exposure time can be linearly scaled to an image at a different exposure time. Dark pixel intensity can be directly measured by obtaining an image at no light and zero (or minimum) exposure time. It can be also indirectly calculated by capturing images at a series of exposure times. Finally, the prestained and poststained images were acquired at their optimal exposures and autofluorescence was completely removed by normalizing images with the exposure time ratio and dark pixel intensity followed by subtraction.     

用构造光系统实现3-D形貌测量的研究

介绍了一个用构造空间二进制编码进行非接触３Ｄ形貌测量的系统。它以一台ＬＣＤ投影仪为硬件基础,用８幅条纹投影图案对被测物体表面进行空间编码。用ＣＣＤ摄像机获取物体编码信息,用基于单一像素的三角法原理从摄像机图像中获取三维形貌数据。指出了二进制编码图案生成软件及其生成的条纹图案的特点。为了提高３Ｄ形貌测量的精度,分析了由摄像机和投影仪镜头造成的误差,建立了它们的透镜误差矫正公式,并取得了良好的实验结果。     

用构造光系统实现3-D形貌测量的研究

介绍了一个用构造空间二进制编码进行非接触3-D形貌测量的系统。它以一台LCD投影仪为硬件基础,用8幅条纹投影图案对被测物体表面进行空间编码。用CCD摄像机获取物体编码信息,用基于单一像素的三角法原理从摄像机图像中获取三维形貌数据。指出了二进制编码图案生成软件及其生成的条纹图案的特点。为了提高3-D形貌测量的精度,分析了由摄像机和投影仪镜头造成的误差,建立了它们的透镜误差矫正公式,并取得了良好的实验结果。     

改进的高光边缘颜色恒常性算法研究

图像的高光区域包含丰富的光源信息,对颜色恒常性研究具有重要价值。然而,由于自然场景的动态范围往往会超过常用数码相机中传感器所能捕获的范围,高光区域易产生过曝光。针对过曝光现象,提出了一种过曝光区域恢复的高光边缘颜色恒常算法。该算法对高光边缘权重进行了2次优化。第1次优化在过曝光区域校正部分,利用过曝光区域自动校正算法恢复出高光区域的边缘信息,得到高动态范围图像;然后通过迭代算法将图像梯度投影到估计出的光源方向上,得到高光边缘权重的第2次优化;最后将优化后的高光边缘方向作为光源方向的估计。实验表明,对于自然场景图像,特别是其中过曝光明显的图像,该算法有效地解决了权重灰边颜色恒常算法中高光边缘不准确的问题,大大提高了光源估计的准确性。     

数字微镜器件在高动态辐射场景成像探测系统中的应用

由于数字微镜器件（DMD）空间光调制器结合图像传感器能同时探测高动态场景中的亮暗目标,本文研究了DMD在高动态辐射场景成像探测系统中的应用。首先,介绍了DMD实现成像探测的原理,分析了DMD在高动态场景成像探测系统中的驱动控制方法。然后,根据DMD在高动态辐射场景成像探测系统中的工作特性,设计了能使光电成像设备提高66 dB的DMD的驱动控制。文中阐述了系统的主要设计模块和工作参数,并结合实验验证了系统设计的正确性。实验结果表明：该驱动控制方法能够实现对高动态场景中亮暗目标的同时探测,满足对光电成像设备动态范围提高66 dB的要求。若光电成像设备采用11位高灵敏高动态科学级图像传感器,则系统动态范围可达130 dB以上。     

Simultaneous correction of flat field and nonlinearity response of intensified charge-coupled devices

Intensified charge-coupled devices (ICCDs) are used extensively in many scientific and engineering environments to image weak or temporally short optical events. Care has to be taken in interpreting the images from ICCDs if quantitative results are required. In particular, nonuniform gain (flat field) and nonlinear response effects must be properly accounted for. Traditional flat-field corrections can only be applied in the linear regime of the ICCD camera, which limits the usable dynamic range. This paper reports a more general approach to image correction whereby the nonlinear gain response of each pixel of the ICCD is characterized over the full dynamic range of the camera. Image data can then be corrected for the combined effects of nonuniform gain and nonlinearity. The results from a two-color pyrometry measurement of soot field temperature are used to illustrate the capabilities of the new correction approach.     

复杂场景机械交错拼接遥感相机在轨相对定标

为了实现机械交错拼接型(TDICCD)遥感相机高频次、高精度相对辐射定标,本文提出一种面向复杂场景的在轨非均匀性校正方法。该方法在相机绕偏航轴旋转前后进行正交二次成像,利用所获取的偏航成像数据、常规成像数据分别对阵列内、阵列间探元进行相对定标;结合复杂场景宽辐射动态范围的特点,利用多点曲线拟合的方法实现相对定标参数解算,最终达到非均匀性校正的目的。利用仿真成像数据对均匀场景以及复杂场景进行相对辐射定标试验,结果表明,在非均匀场景中经复杂场景正交二次成像定标(OSICCS)后图像非均匀性NU系数相较于常用方法定标后图像非均匀性NU系数降低了0.499 1%以上,条纹条带噪声以及残余条带噪声得到有效去除。     

Determining image distortion and PBS (point of best symmetry) in digital images using straight line matrices

It is impossible to take accurate measurements in photogrammetry without first removing the distortion in images. This paper presents a methodology for correcting radial and tangential distortion and for determining the PBS (Point of Best Symmetry) without knowledge of the interior orientation parameters (IOPs). An analytical plumb-line calibration method is used, measuring only the coordinates of points on straight lines, regardless of the position and direction of these lines within the image. Points belonging to multiple lines can also be used since the effects on their X and Y coordinates are calculated independently. The results obtained on an image of a common scene, taken with a handheld non-metric camera, show a high degree of accuracy even with a minimum number of observables. And its application on a calibrated grid for engineering purposes with a semi-metric camera, results optimal even using a single image.     

一种基于REC.2020高清色域的视频级显微高动态范围成像方法

高动态范围成像已经成为数字显微镜发展的一大趋势。目前视频级高动态范围显微成像技术由于计算复杂度较高,还无法做到实时处理和显示。提出利用高清电视领域中的REC.2020色域变换,结合GPU实时加速处理技术,成功实现了高动态范围显微图像视频流的实时显示,图像具有良好的色彩还原性和细节恢复性。实验结果表明,设计的算法不仅能够提供稳定的高清、高动态范围视频,其细节和色彩还原性也有了很大的提高,突破了传统的高动态范围图像技术在成像速度和质量方面的限制。