Use of a wide angle CCD line camera for BRDF measurements

In order to determine the Bi-directional Reflectance Distribution Function (BRDF) of natural surfaces a CCD line camera is used. This allows measurements under natural conditions with a high azimuth and zenith angular resolution in a short time. The CCD line spans a field of view of 80° as the zenith angle range. For covering the azimuth range, the camera is mounted on a rotating device and an extendible boom provides an aerial platform. This set up allows the measurement of the [almost] complete reflectance distribution of the surface below the camera for the 30-s rotation period of the camera. The camera used for this set up is the wide angle airborne camera (WAAC), which was developed at the DLR for airborne stereo imaging purposes. This paper presents the radiometric calibration of the system and shows the initial results of our approach in measuring the BRDF with high angular resolution for a short period.     

一种彩色面阵CCD测绘相机前向像移的补偿方法

 为了实现对前向像移的补偿,提出一种通过合理调整快门曝光时间和飞机速高比之间的关系来补偿前向像移的方法,对前向像移产生的原因进行研究。介绍彩色面阵CCD工作原理、相机工作原理,从光学系统成像原理的角度分析产生前向像移的原因,还分析了速高比和曝光时间误差。实验结果表明：速高比误差和曝光时间误差均可控制在合理误差范围内,满足前向像移量小于1.5个像元尺寸的补偿要求,达到了测绘相机的精度指标。     

Single-shot line scan imaging using stimulated echoes

A new high-speed MRI method is described for single-shot line scan imaging (LSI) based on stimulated echoes (STE). To allow for multislice imaging, the technique comprises a series of slice-selective preparation pulses (each corresponding to the first RF pulse of a STE sequence), a slab-selective refocusing pulse (second RF pulse), and multiple line-selective read pulses (third RF pulses). An alternative version employs packages of two slice-selective pulses followed by multiple line-selective read pulses. Experimental applications deal with human brain imaging on a clinical MRI system at 2.0 T. The technique offers user-selectable trade-offs between volume coverage (1-15 sections) and in-plane spatial resolution (1-5 mm linear pixel dimension) within total acquisition times of less than 500 ms. Although LSI yields a lower signal-to-noise ratio than Fourier imaging, single-shot LSI with STEs is free from resonance offset effects (e.g., magnetic field inhomogeneities and susceptibility differences) that are typical for echo-planar imaging. Moreover, the technique exhibits considerable robustness against motion and provides access to arbitrary fields-of-view, i.e., localized imaging of inner volumes without aliasing artifacts due to phase wrapping.     

Estimating color appearance of pearlescent bottles using digital camera

Pearlescent coatings become highly popular to the modern generation of color rendering materials due to their unique color effect. However, it is quite challenging to evaluate its color appearance by traditional color measurement. A low-cost camera is a highly efficient device for multi-geometry color appearance estimation for pearlescent bottles, which has been achieved through the camera characterization, sample image capturing, and then mathematical transforming from RGB （red, green, and blue） values to color appearance attributes based on the color appearance model of CIECAM02. A tele-spectroradiometer for physical measurement together with visual assessment is applied for comparison with the camera method to evaluate the accuracy of camera predictions and discuss the applicability of CIECAM02. The experimental results indicate that the camera data have strong correlation with the physical measurement and also fit well with visual data except for a slight slope shift existing in lightness due to a divinable psychophysical magnitude variation for spatial-dependent color samples. Hence it is feasible to estimate the color appearance of pearlescent bottles using a digital camera.     

使用多个线阵CCD-计算机系统实时监控多界面位置

本文提出一套多界面位置实时监控系统。该系统采用八个线阵ＣＣＤ像感器分别接收每个界面的光学图像。按照控制程序的设定，适时点亮界面的照明光源，同时驱动ＣＣＤ开始工作，并在采集完界面位置信息后，关掉照明光源及ＣＣＤ，以延长系统的寿命，实现长期连续工作。为了同时分别监控多个界面，设计了专用微机接口电路，通过硬件电路实现各界面数据的同时锁存，然后将每个ＣＣＤ的光电信号采入计算机，解决了目视读数无法保证多处数据在时间上一致性的困扰。运用该系统监控多处油水界面，每处均可在１００ｍＬ体积的检测管内测量到０．１ｍＬ的界面变化。     

同轴三反线阵空间相机宽视场波前误差的在轨检测方法

针对同轴偏场三反射镜系统,提出了一种宽视场波前误差检测方法。通过3个视场的波前误差检测,得到相应视场像差的Zernike多项式系数,利用该Zernike多项式系数减去设计误差后,随视场的变化为二次曲线,通过抛物线插值即可得到任一视场的Zernike多项式系数。仿真研究了Zernike多项式系数随视场的变化以及拟合精度等问题。仿真结果表明:对于原始设计误差,其Zernike系数随视场的变化需要用3次或4次曲线拟合;对于由主镜面形误差、次镜位置误差、次镜面形误差和三镜面形误差等引起的各视场波前误差,其Zernike系数随视场的变化可用直线或2次曲线拟合。通过事先存贮设计误差,仅需3个波前传感器即可实现全视场波前误差估计。Zernike系数估计误差在10-5量级。     

三线阵测绘相机光学系统的杂光分析与计算

针对光学系统的杂光导致三线阵测绘相机成像质量下降的问题,根据光学系统的设计结果,对相机入口处的杂光能量、像面杂光辐照度、杂光系数等进行了分析与计算,提出了合理的杂光抑制措施。利用ThermalDesktop软件和Light—Tools软件,对三线阵立体测绘相机各光学系统进行分析与模拟计算,得到其杂光系数均小于5％。最后进行了光学实验,并利用面源法测试了杂光系数。检测结果验证了杂光分析与研究方法的正确性以及杂光抑制措施的可行性。     

Gradient-echo line scan imaging using 2D-selective RF excitation

A gradient-echo line scan imaging technique was developed which employs two-dimensional spatially selective radiofrequency (2DRF) pulses for consecutively exciting individual columns of transverse magnetization, i.e., image lines. Although a variety of trajectories are possible for 2DRF excitation, the current implementation involved a blipped-planar trajectory in conjunction with additional saturation RF pulses to suppress side excitations above and below the desired image section, i.e., along the blip direction of the 2DRF pulse. Human brain imaging at 2.0 T (Siemens Vision, Erlangen, Germany) resulted in measuring times of 5.2 s for a 5-mm section at 1.0 x 1.0 mm in-plane resolution. Functional neuroimaging of the motor cortex at 1.2 s temporal resolution and 0.78 x 1.56 mm in-plane resolution exploited the capability of imaging inner volumes (here a 25-mm strip) without signal aliasing.     

Simultaneous two-axis shearographic interferometer using multiple wavelengths and a color camera

Multi-component measurements in shearography and other applications of Electronic Speckle Pattern Interferometry (ESPI) are typically achieved using multiple optical configurations that are activated sequentially to measure each desired quantity separately. A novel optical setup is introduced here where orthogonal shearography measurements are simultaneously made using a single color-camera imaging multiple monochromatic light sources of different wavelengths. The Red–Green–Blue (RGB) sensors of a conventional Bayer type camera are read separately, thereby providing three independent color signals and independent ESPI phase maps. Orthogonal axis shearography is achieved using a modified shearography interferometer where a dichroic filter is added to provide a second wavelength-dependent measurement. The availability of the two surface slopes gives the opportunity for the data to be summed numerically to give the surface displacement shape. This application is of significant practical interest because the surface displacement measurement can be made under field conditions by taking advantage of the well-known optical stability of shearography measurements. The two simultaneously measured surface slopes also offer the possibility to mathematically compensate for non-uniformity and non-orthogonality in the image shear caused by mirror non-flatness and/or mirror misalignments.     

A novel color image encryption scheme using alternate chaotic mapping structure

This paper proposes an color image encryption algorithm using alternate chaotic mapping structure. Initially, we use the R, G and B components to form a matrix. Then one-dimension logistic and two-dimension logistic mapping is used to generate a chaotic matrix, then iterate two chaotic mappings alternately to permute the matrix. For every iteration, XOR operation is adopted to encrypt plain-image matrix, then make further transformation to diffuse the matrix. At last, the encrypted color image is obtained from the confused matrix. Theoretical analysis and experimental results has proved the cryptosystem is secure and practical, and it is suitable for encrypting color images.     

真空紫外反射率计用于BRDF的测量

：介绍了一种真空紫外反射率计,采用间接测量方法,在该反射率计测试了聚四氟乙烯漫反射板的双向反射率分布函数（ＢＲＤＦ）,正入射时该聚四氟乙烯漫反射板１５°到７５°的双向反射率分布函数偏差为１３％。     

彩色数字摄像机控制参数影响的标定

当彩色CCD数字摄像机作为测量设备应用时,必须清楚地了解输入光强信号和输出信号之间的关系,明确各控制参数对信号的影响。依据彩色CCD数字摄像机原理和相关文献,建立起一般性的信号传递函数,针对于特定型号的彩色CCD数字摄像机,通过积分球测试实验对信号传递函数中相关影响参数进行标定分析,验证其影响方式和适用范围。     

Out-of-focus color camera calibration with one normal-sized color-coded pattern

Conventional camera calibration methods always require well-focused target images for accurate feature detection. This requirement brings many challenges for long-range vision systems, due to the difficulty of fabricating an equivalent size target to the sensing field-of-view (FOV). This paper presents an out-of-focus color camera calibration method with one normal-sized color-coded pattern as the calibration target. The red, green and blue (RGB) channels of the color pattern are encoded with three phase-shift circular grating (PCG) arrays. The PCG centers used as feature points are extracted by ellipse fitting of the 2π-phase points. Experiments demonstrate that the proposed method can achieve accurate calibration results even under severe defocus.     

隐秘型CCD微摄像镜头光学设计

为了满足隐秘型ＣＣＤ摄像光学系统的广角视场、长工作距离、小空间尺寸、隐蔽性能好、成像质量优良等特殊要求。提出一种以同心透镜作为负组,置孔径光阑于镜头前方的新型反远摄结构。对其设计思想、像差特点进行了分析,并给出了ｆ′＝３６ｍｍ,２ω＝８０°,ｌＦ′／ｆ′＝１１的隐秘型ＣＣＤ微摄像镜头的像差和传函计算曲线     

摆扫式TDI-CCD航空相机传感器MTF分析

TDI-CCD与普通线阵CCD相比具有很多优点,因而广泛应用于航空航天成像领域。在介绍TDI-CCD特点和摆扫式TDI-CCD航空相机扫描成像原理的基础上,分析了扫描像移的大小及行周期,推导出了由几何尺寸、电荷转移损失率、电荷分立运动、速度失配等因素引起图像传感器的调制传递函数退化表达式,给出了传感器线列方向和TDI方向的调制传递函数,提出了提高传感器调制传递函数的几种方法,对TDI-CCD航空相机整机设计提供了参考。     

三线阵CCD立体测绘相机的集成装调

考虑几何精度对三线阵CCD立体测绘相机测绘精度的影响,研究了测绘相机组合体的装调方法以建立和保证相机的空间几何关系。首先,介绍了测绘相机组合体的结构和坐标系的定义;其次,提出了各基准立方镜和相机的装调要求;最后,确定了多相机集成装调流程,重点介绍了测绘相机的装调步骤。装调结果表明：各相机的光学传递函数〉0.2,畸变〈0.03%,测绘相机的空间几何关系满足要求,提出的集成装调技术有效地保证了测绘相机的空间几何关系。     

An adaptively spatial color gamut mapping algorithm

To improve the accuracy of color image reproduction from displays to printers, an adaptively spatial color gamut mapping algorithm （ASCGMA） is proposed. In this algorithm, the compression degree of out- of-reproduction-gamut color is not only related to the position of the color in CIELCH color space, but also depending on the neighborhood of the color to be mapped. The psyehophysical experiment of pair comparison is carried out to evaluate and compare this new algorithm with the HPMINDE and SGCK gamut mapping algorithms recommended by the International Commission on Illumination （CIE）. The experimental results indicate that the proposed algorithm outperforms the algorithms of HPMINDE and SGCK except for the very dark images.     

巧用数码相机使运动定格

许多实验过程持续时间短,速度快,不便于观察. 用数码相机的摄像功能摄录运动的全过程,再逐帧播放,即可清晰再现实验结果,便于客观准确地得出结论.     

A new method of ultrasound color flow mapping

Conventional ultrasound color flow mapping systems estimate and visualize only the axial velocity component. To obtain the transverse velocity component a modification of a multiple-beam method is proposed. The new two-dimensional color flow mapping system has a small size and consists of three transducers. The central transducer is an appodized and focused phased array. The other transducers are unfocused probes. Three transducers act as receivers and the central transducer operates as a transmitter. All receivers acquire rf scan lines that are then processed to estimate three axial velocity components using an autocorrelation method. These estimates are then combined to estimate the transverse velocity component, taking into account the geometric relationships among three transducers. Two algorithms for transverse velocity estimation are proposed. The first uses the Doppler angle estimate for calculation of the transverse velocity component. The other algorithm calculates the transverse velocity component directly from the axial components. The accuracy of the flow velocity estimators is estimated by simulations. Analysis of accuracy allows choosing the more effective algorithm for two-dimensional velocity estimation, which is insensitive to variations of the Doppler angle.