Multiple LED camera for dynamic photoelasticity

Dynamic photoelasticity involves the high-speed recording of rapidly moving fringe patterns in synchronization with loading. Cranz Schardin cameras are routinely utilized in the recording of dynamic photoelastic patterns. There are no moving components in these cameras, making the setup simple and attractive. Amultiple LED camera based on the Cranz Schardin format is presented. Highspeed instant polaroid film is used for recording the photoelastic fringes. Low cost, simplicity in the experimental setup, and rapid repeatability are the advantages of the camera.     

彩色数码相机光强响应特性的标定实验

当前高动态彩色数码相机的光强响应具有强烈的非线性,针对于此,用多项式这种非线性模型对彩色数码相机红、绿、蓝三通道的光强响应特性予以描述。建立了一种利用曝光时间测量CCD彩色数码相机光强响应特性的方法,通过调整快门速度获得不同的光强。同时,设计了标定实验,选用OLYMPUSE20数码相机对上述理论分析成果进行了实验验证,分别采用多项式模型和幂模型对实验数据进行拟合。实验结果表明,光强响应标定方法是可行的,多项式模型更适于描述彩色数码相机光强响应特性。     

一种基于移动像机的大型结构件形变监测方法

针对大型结构安全监测中测量设备多、分布复杂、价格昂贵等问题,提出一种基于摄像测量技术的移动式工业像机在线监测方法。通过不同视图之间的极线约束关系推导运动平台以及像机在不同时刻外参数的约束关系。利用简单数据融合方法将像机运动外参数与运动轨迹解算的像机外参数进行融合,达到自动在线测量像机外参数的目的,从而解出标识点的精确位置,实现测量过程的自动化。实验结果表明:提出的测量方法装置简单,精度较高,可以应用于大型复杂结构的在线形变安全监测。     

基于数码摄像技术的高耸结构动态特性监测

在结构健康监测领域,基于数码摄像的图像处理技术作为一种新的结构振动监测方法正受到广泛关注。以主结构建成后的广州新电视塔为研究背景,利用工业数码摄像机对其在一般风荷载作用下的动态特性进行监测试验,并与GPS和加速度计同时测量。数据分析结果表明,利用数码摄像系统获得的塔顶动位移时程曲线与GPS获得的动位移曲线吻合得较好;利用数码摄像技术能够准确的识别高耸结构的低阶振动频率,其获得的结构一阶振动频率,与GPS、加速度计识别结果以及有限元分析结果吻合得很好。研究结果表明,在高耸结构的健康监测中,应用数码摄像技术进行结构动态特性监测是一种有效的新方法。     

基于数码相机特性文件的色彩校正和色彩管理研究

阐述了颜色特性文件的作用,分析了数码相机颜色特性文件的制作过程和使用原理,并对使用数码相机颜色特性文件进行色彩校正和色彩管理进行了研究,有效的实现了数码相机的色彩还原和保证了颜色复制过程中的一致性.     

2003年数码相机大盘点

~~2003年数码相机大盘点     

Multiple-scattering suppression in dynamic light scattering based on a digital camera detection scheme

We introduce a charge-coupled device (CCD) camera-based detection scheme in dynamic light scattering that provides information on the single-scattered autocorrelation function even for fairly turbid samples. It is based on the single focused laser beam geometry combined with the selective cross-correlation analysis of the scattered light intensity. Using a CCD camera as a multispeckle detector, we show how spatial correlations in the intensity pattern can be linked to single- and multiple-scattering processes. Multiple-scattering suppression is then achieved by an efficient cross-correlation algorithm working in real time with a temporal resolution down to 0.02 s. Our approach allows access to the extensive range of systems that show low-order scattering by selective detection of the singly scattered light. Model experiments on slowly relaxing suspensions of titanium dioxide in glycerol were carried out to establish the validity range of our approach. Successful application of the method is demonstrated up to a scattering coefficient of more than micro(S) = 5 cm(-1) for the sample size of L = 1 cm.     

Experimental study of dry stone masonry walls using digital reflection photoelasticity

Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five-step phase-shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non-uniformity of block geometry even in very regular dry stack masonry.     

如何识别水货数码相机

一般来说,水货的价格要比行货低一些,但我们绝不能只从价格高低就断定哪个型号的DC是不是水货。由于水货数码相机大都不是在国内生产的,往往没有中文说明书,说明书都是日文或者英文的（日本讲究环保,包装盒都是再生纸和简单印刷的）,香港行货（我们称之为水货）的说明书是繁体中文的。一般都是日文和繁体中文包装,驱动程序、软件等上面也没有中文。     

Cone-beam tomography with a digital camera

We show that x-ray computer tomography algorithms can be applied with minimal alteration to the three-dimensional reconstruction of visible sources. Diffraction and opacity affect visible systems more severely than x-ray systems. For camera-based tomography, diffraction can be neglected for objects within the depth of field. We show that, for convex objects, opacity has the effect of windowing the angular observation range and thus blurring the reconstruction. For concave objects, opacity leads to nonlinearity in the transformation from object to reconstruction and may cause multiple objects to map to the same reconstruction. In x-ray tomography, the contribution of an object point to a line integral is independent of the orientation of the line. In optical tomography, however, a Lambertian assumption may be more realistic. We derive an expression for the blur function (the patch response) for a Lambertian source. We present experimental results showing cone-beam reconstruction of an incoherently illuminated opaque object.     

数码相机品牌防伪的鉴别

随着人们生活水平的提高和外出旅游的普及,数码相机早已成了家家必备的生活用品。数码相机的热销带来了一系列的品质和销售问题,虽然有相关执法部门的市场监督和管理,但各大主流品牌厂商为了维护消费者的利益和自身的信誉,都尽了最大的努力来保护数码相机市场的纯净,各大品牌商品的包装上都采用了一系列防伪技术。这里就给大家列出了11家主要品牌的鉴别方法。     

Assessment of autonomous phase unwrapping of isochromatic phase maps in digital photoelasticity

Photoelasticity is the only whole-field experimental technique which can analyse both 2-D and 3-D elasticity problems. In digital photoelasticity one gets two phase maps, one corresponding to principal stress direction (isoclinic) and the other corresponding to principal stress difference (isochromatic). The phase maps for both isoclinics and isochromatics are to be unwrapped differently for obtaining continuous phase values. Autonomous phase unwrapping is one of the challenging issues and this paper focuses on recent advances on isochromatic phase map unwrapping. A comparative study of different autonomous phase unwrapping algorithm is done by solving a bench mark problem and a stress frozen slice with cut-outs. The need for domain delimiting in addition to domain masking is brought out while using autonomous phase unwrapping algorithms.     

数码相机的亮度分布测试研究

在数码相机测光原理和数字图像处理的基础上利用均匀亮度源对数码相机进行光学标定,获取数码相机采集到的图像灰度值与曝光量之间的确切关系,并以此来获得亮度回归公式.在均匀亮度源标定下数码相机的亮度回归曲线的相关系数R2达到了0.984 5.利用标定完的数码相机进行亮度测试时取得了很好的实验效果,并且在进行点目标物亮度测试时相对误差可以控制到5%左右,在进行面目标物亮度分布测试时整体误差基本上可以控制到10%左右.     

是擦肩而过,还是迎头赶上?——略论数码相机和投影电视的进展

介绍和讨论数码相机和投影电视国内外的进展状况     

X-ray imaging using a consumer-grade digital camera

The recent advancements in consumer-grade digital camera technology and the introduction of high-resolution, high sensitivity CsBr:Eu²⁺ storage phosphor imaging plates make possible a new cost-effective technique for X-ray imaging. The imaging plate is bathed with red stimulating light by high-intensity light-emitting diodes, and the photostimulated image is captured with a digital single-lens reflex (SLR) camera. A blue band-pass optical filter blocks the stimulating red light but transmits the blue photostimulated luminescence. Using a Canon D5 Mk II camera and an f1.4 wide-angle lens, the optical image of a 240×180 mm² Konica CsBr:Eu²⁺ imaging plate from a position 230 mm in front of the camera lens can be focussed so as to laterally fill the 35×23.3 mm² camera sensor, and recorded in 2808×1872 pixel elements, corresponding to an equivalent pixel size on the plate of 88 μm. The analogue-to-digital conversion from the camera electronics is 13 bits, but the dynamic range of the imaging system as a whole is limited in practice by noise to about 2.5 orders of magnitude. The modulation transfer function falls to 0.2 at a spatial frequency of 2.2 line pairs/mm. The limiting factor of the spatial resolution is light scattering in the plate rather than the camera optics. The limiting factors for signal-to-noise ratio are shot noise in the light, and dark noise in the CMOS sensor. Good quality images of high-contrast objects can be recorded with doses of approximately 1 mGy. The CsBr:Eu²⁺ plate has approximately three times the readout sensitivity of a similar BaFBr:Eu²⁺ plate.     

Thin-filament pyrometry with a digital still camera

A novel thin-filament pyrometer is presented. It involves a consumer-grade color digital still camera with 6 megapixels and 12 bits per color plane. SiC fibers were used and scanning-electron microscopy found them to be uniform with diameters of 13.9 micro m. Measurements were performed in a methane-air coflowing laminar jet diffusion flame with a luminosity length of 72 mm. Calibration of the pyrometer was accomplished with B-type thermocouples. The pyrometry measurements yielded gas temperatures in the range of 1400-2200 K with an estimated uncertainty of +/-60 K, a relative temperature resolution of +/-0.215 K, a spatial resolution of 42 mum, and a temporal resolution of 0.66 ms. Fiber aging for 10 min had no effect on the results. Soot deposition was less problematic for the pyrometer than for the thermocouple.     

环境激励下基于相关函数的脉冲响应函数重构

在白噪声激励下,结构响应的相关函数作为脉冲响应函数的近似可以进行模态参数辨识,但其物理意义始终缺乏明确解释;相比于脉冲响应函数,基于相关函数的辨识缺少了模态参与因子或者说质量信息,这也是工况模态分析(OMA)方法的主要缺陷。简要回顾了复模态下的自然激励技术原理,证明了白噪声激励下位移响应的相关函数等价于系统在特定初始条件下的自由响应,给出相应初始条件的计算方法;进一步提出了一种系统质量分布的辨识方法,并藉此重构得到系统脉冲响应函数。讨论了相关函数误差与信号时长及激励带宽之间的关系。通过仿真和试验验证了所得结论。     

Factors affecting the intensity distribution in high stress gradient zones in digital photoelasticity

In digital photoelastic analysis it is observed that in high stress gradient zones the fringes become brighter. It leads to erroneous results, if not accounted for, in those techniques which use quantitative values of intensity to evaluate the experimental parameters. In this note, the reasons for the above phenomenon is investigated and suitable recommendations are given.     

基于圆环点的亚像素摄像机自标定方法

针对现有的摄像机自标定算法抗噪声性能差等问题,分析了基于圆环点的摄像机自标定方法的原理,对现有方法作出了改进.充分利用Harris算子和Fostner算子的优点设计了一种亚像素的角点检测算法,提取的角点位置可精确到亚像素级;同时引入了等效圆心的概念,最大限度地降低了噪声干扰.然后充分利用射影几何调和共轭的理论求取摄像机的内参数.实验结果表明,该标定方法原理简单,标定结果鲁棒性较好且标定精度较高,可应用于高精度的视觉测量.     

基于主成分分析的多光谱相机灵敏度优化

研究了基于主成分分析的多通道光谱图像获取硬件系统即多光谱相机的灵敏度优化问题。利用多维向量空间理论和主成分分析法,系统讨论了多光谱获取系统优化灵敏度的理论和方法。提出灵敏度优化向量的概念,将滤光片透过率优化和光源辐射谱优化两种方法统一起来。利用四种灵敏度优化向量进行了仿真试验,并给出了在主成分分析算法下的实验仿真结果。结论是：多光谱系统灵敏度优化向量的正交化设计是系统光谱图像获取的必要要求;窄带灵敏度中,交叠的灵敏度优化向量具有更好的光谱反射率信息获取能力;在有限数目的宽带滤色片中,挑选滤色片透过率向量可以得到较好的多光谱相机的灵敏度向量。