Phase volume holographic optical components for high-brightness single-LCD projectors

Projection systems based on liquid-crystal displays (LCD's) offer new opportunities to display high-definition and large-size TV images. There are two types of LCD projector architectures: the 3-LCD architecture uses one LCD for each primary color, red, green, and blue, whereas a single-LCD configuration employs only one LCD paved with color filters. The single-LCD projector is simple and compact but suffers from a poor luminous efficiency because of losses in the color filters: each filter transmits only ~1/3 of the flux emitted by the lamp. To increase this optical efficiency, we propose to introduce volume holographic elements in the architecture of a single-LCD projector. Innovative systems are presented in which volume holographic elements realize the spatiochromatic illumination of the LCD. This illumination consists of selectively directing all the light that corresponds to a primary color, red, green, or blue, in the pixel addressed with the corresponding video composite signal and exploits the spectral selectivity and dispersion properties of volume holographic gratings and lenses. The two main advantages of such illumination are the suppression of the color filters and the recovery of the light lost in a classical architecture by absorption of the color filters. A complete luminous efficiency analysis of spatiochromatic illumination with volume holographic elements is presented. The achieved performances are compared with classical single-LCD projectors.     

Recovering fluorescent spectra with an RGB digital camera and color filters using different matrix factorizations

The aim of a multispectral system is to recover a spectral function at each image pixel, but when a scene is digitally imaged under a light of unknown spectral power distribution (SPD), the image pixels give incomplete information about the spectral reflectances of objects in the scene. We have analyzed how accurately the spectra of artificial fluorescent light sources can be recovered with a digital CCD camera. The red-green-blue (RGB) sensor outputs are modified by the use of successive cutoff color filters. Four algorithms for simplifying the spectra datasets are used: nonnegative matrix factorization (NMF), independent component analysis (ICA), a direct pseudoinverse method, and principal component analysis (PCA). The algorithms are tested using both simulated data and data from a real RGB digital camera. The methods are compared in terms of the minimum rank of factorization and the number of sensors required to derive acceptable spectral and colorimetric SPD estimations; the PCA results are also given for the sake of comparison. The results show that all the algorithms surpass the PCA when a reduced number of sensors is used. The experimental results suggest a significant loss of quality when more than one color filter is used, which agrees with the previous results for reflectances. Nevertheless, an RGB digital camera with or without a prefilter is found to provide good spectral and colorimetric recovery of indoor fluorescent lighting and can be used for color correction without the need of a telespectroradiometer.     

基于单目视觉的四旋翼飞行器目标跟踪算法研究

以AR.drone四旋翼飞行器为研究平台,提出一种基于AR.drone前置单目摄像头,并结合卡尔曼滤波跟踪视频中移动目标的方法。将采集得到的RGB图像经过颜色空间转换成对光照变化影响不大的HSV图像;通过OpenCV对视频中跟踪目标的图像去噪,对轮廓进行检测寻找图像中最大的轮廓目标,并通过卡尔曼滤波对目标位置进行修正;计算四旋翼飞行器的飞行朝向并实现四旋翼飞行器对视频区域里移动目标的跟踪。实验表明,该方法有效地实现了对移动目标跟踪的准确性、稳定性和快速性。     

In vivo 783-channel diffuse reflectance imaging system and its application

A fiber-based reflectance imaging system was constructed to produce in vivo absorption spectroscopic images of biological tissues with diffuse light in the cw domain. The principal part of this system is the 783-channel fiber probe, composed of 253 illumination fibers and 530 detection fibers distributed in a 20x20 mm square region. During illumination with the 253 illumination fibers, diffuse reflected lights are collected by the 530 detection fibers and recorded simultaneously as an image with an electron multiplying CCD camera for fast data acquisition. After signal acquisition, a diffuse reflectance image was reconstructed by applying the spectral normalization method we devised. To test the applicability of the spectral normalization, we conducted two phantom experiments with chicken breast tissue and white Delrin resin by using animal blood as an optical inhomogeneity. In the Delrin phantom experiment, we present images produced by two methods, spectral normalization and reference signal normalization, along with a comparison of the two. To show the feasibility of our system for biomedical applications, we took images of a human vein in vivo with the spectral normalization method.     

Optical video interpretation of interference colors from thin transparent films on silicon

A method is tested for analyzing color video images to determine film thickness for transparent coatings on silicon. The method is robust to reasonable variations in light level, video parameters, and computer image capture spectral characteristics. The main standardizing feature of the method is to include characterization of a bare substrate along with the unknown samples (either within the view frame or as a separate sequence under identical illumination conditions during video capture). Then, the color appearance for the unknown sample can be referenced to the color appearance of the bare substrate, thereby enabling a quantitative match between the measured color and the predicted color characteristics. The technique is tested with transparent spin-on-glass (SOG) coatings that were calibrated separately. The limits of applicability and the level of accuracy that can be obtained are discussed in detail.     

A method to estimate correlated color temperatures of illuminantsusing a color video camera

An indirect method of estimating light source color or the correlated color temperature of illuminants is proposed. It incorporates a color video camera with fixed white balance, a set of known color chips, and a desktop microcomputer. The correlated color temperature of the light source illuminating the color chips is estimated. The mathematical method used is the estimation of functions to be integrated from several values of the definite integrations. These values, which are measurable, are given as the output of the color video camera under different conditions. By means of the method of least squares, estimation accuracies of from 0.1 to 1.4% of the correlated color temperature are achieved. The accuracy achieved depends on the spectral distribution of the illuminants, except for illuminants like fluorescent lamps     

电视摄像机主要参数测试系统设计与实施

在监控和军事等领域应用中,对电视摄像机的主要光电参数的准确标定是非常重要的。本文介绍了一种基于视频信号处理的电视摄像机主要光电参数综合检测装置的设计和实施方案。采用特定的测试目标对摄像机成像,视频图像被高精度数字图像采集卡捕获并将数据传送给计算机,再通过数字图像处理软件自动计算,可实现CCD响应度、灵敏度、信噪比、动态范围和电视分辨力、畸变、对比度等参数的准确测试。     

Axi-vision camera (real-time distance-mapping camera)

The camera described here makes color TV images that include information about the distance between the camera and the objects in the images. This range information is obtained from two images of the same scene taken under different illumination conditions. The camera does not require scanning, multiple camera units, or complicated computation. Range information for each pixel is acquired fast enough to keep up with the video rate of a TV camera. We describe various operational features and technical specifications such as ranging errors as well as the results of experimental investigations of the dependence on the color and reflectivity of the objects, of the sensitivity to interference from external light, and of the effects of the movement of the objects.     

Adaptive optics with advanced phase-contrast techniques. I. High-resolution wave-front sensing

High-resolution phase-contrast wave-front sensors based on phase spatial light modulators and micromirror/ liquid-crystal arrays are introduced. Wave-front sensor performance is analyzed for atmospheric-turbulence-induced phase distortions described by the Kolmogorov and the Andrews models. A high-resolution phase-contrast wave-front sensor (nonlinear Zernike filter) based on an optically controlled liquid-crystal phase spatial light modulator is experimentally demonstrated. The results demonstrate high-resolution visualization of dynamically changing phase distortions within the sensor time response of approximately 10 ms.     

一种基于数字图像合成的扩展动态范围方法

数码相机中CCD/CMOS图像传感器的饱和电流和背景噪音使得一次曝光很难超过60-80dB 的动态范围。根据人眼对灰度图像的识别特性,可以采用对相同景物二次不同曝光图像软件合成的算法来获取高动态范围的图像。实验结果显示,当景物画面各部分光照明显差别时,这种方法能有效地获得全部细节信息。     

Liquid-crystal adaptive optics based on feedback interferometry for high-resolution retinal imaging

A novel, to our knowledge, adaptive optical imaging system for high-resolution retinal imaging is described. The system is based on a feedback interferometer, in which two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is fed back, with the help of a video projector connected with a CCD camera, to an optically addressed phase-only liquid-crystal spatial light modulator. Experiments to verify the system performance have been conducted by use of an artificial eye consisting of a lens, an aberration plate, and a resolution test target. We observed that an image of the test target (mimicking a retina) blurred by the aberration plate (mimicking ocular aberrations) was successfully restored immediately after our adaptive optics system was activated.     

Dual in-plane electronic speckle pattern interferometry system with electro-optical switching and phase shifting

A dual in-plane electronic speckle pattern interferometry (ESPI) system has been developed for in situ measurements. The optical setup is described here. The system uses an electro-optical switch to change between the illumination directions for x and y sensitivity. The ability of the electro-optic device to change the polarization of the laser light forms the basis of this switch. The electro-optic device is a liquid-crystal layer cemented between two optically flat glass plates. An electric field can be set up across the layer by application of a voltage to electrodes. The speckle interferometry system incorporates two additional liquid-crystal devices to facilitate phase shifting, and the overall system is controlled by advanced software, which allows switching between the two perpendicular planes in quasi real time. The fact that there are no moving parts is an advantage in any ESPI system for which mechanical stability is vital.     

Characterization of natural illuminants in forests and the use of digital video data to reconstruct illuminant spectra

We describe illumination spectra in forests and show that they can be accurately recovered from recorded digital video images. Natural illuminant spectra of 238 samples measured in temperate forests were characterized by principal-component analysis. The spectra can be accurately approximated by the mean and the first two principal components. Compared with illumination under open skies, the loci of forest illuminants are displaced toward the green region in the chromaticity plots, and unlike open sky illumination they cannot be characterized by correlated color temperature. We show that it is possible to recover illuminant spectra accurately from digital video images by a linear least-squares-fit estimation technique. The use of digital video data in spectral analysis provides a promising new approach to the studies of the spatial and temporal variation of illumination in natural scenes and the understanding of color vision in natural environments.     

Enhance Egocentric Grasp Recognition Based Flex Sensor Under Low Illumination

Egocentric recognition is exciting computer vision research by acquiring images and video from the first-person overview. However, an image becomes noisy and dark under low illumination conditions, making subsequent hand detection tasks difficult. Thus, image enhancement is necessary to make buried detail more visible. This article addresses the challenge of egocentric hand grasp recognition in low light conditions by utilizing the flex sensor and image enhancement algorithm based on adaptive gamma correction with weighting distribution. Initially, a flex sensor is installed to the thumb for object manipulation. The thumb placement that holds in a different position on the object of each grasp affects the voltage changing of the flex sensor circuit. The average voltages are used to configure the weighting parameter to improve images in the image enhancement stage. Moreover, the contrast and gamma function are used to adjust varies the low light condition. These grasp images are then separated to be training and testing with pre-trained deep neural networks as the feature extractor in YOLOv2 detection network for the grasp recognition system. The proposed of using a flex sensor significantly improves the grasp recognition rate in low light conditions.     

Optimum sensors for color constancy in scenes illuminated by daylight

The apparent color of an object within a scene depends on the spectrum of the light illuminating the object. However, recording an object's color independent of the illuminant spectrum is important in many machine vision applications. In this paper the performance of a blackbody-model-based color constancy algorithm that requires four sensors with different spectral responses is investigated under daylight illumination. In this investigation sensor noise was modeled as gaussian noise, and the responses were quantized using different numbers of bits. A projection-based algorithm whose output is invariant to illuminant is investigated to improve the results that are obtained. The performance of both of these algorithms is then improved by optimizing the spectral sensitivities of the four sensors using freely available CIE standard daylight spectra and a set of lightness-normalized Munsell reflectance data. With the optimized sensors the performance of both algorithms is shown to be comparable to the human visual system. However, results obtained with measured daylight spectra show that the standard daylights may not be sufficiently representative of measured daylight for optimization with the standard daylight to lead to a reliable set of optimum sensor characteristics.     

彩色摄像机彩色重现性改善的一种方法

本文在彩色摄像机实际光谱特性曲线未知,并与理论光谱特性曲线又存在偏离情况下使用线性变换原理,提出一种改善摄像机彩色重现性的方法。     

提高镭射光柱卡纸色标光检测信号识别精度研究

目的 针对凹版印刷以镭射光柱纸作为承印物,镭射光柱对色标检测传感器产生干扰,致使镭射光柱纸不能使用传统套印工艺进行印刷,提出一种可直接在镭射光柱区域直接印刷套准色标的新工艺与技术方案。方法 对色标传检测感器检测原理进行分析,分析镭射光柱纸的特点以及对色标传感器造成的干扰。根据镭射光柱光谱反射率曲线来进行滤光镜片的选取,同时也加入衰减镜片以及消光膜进行组合实验测量电压,实验使用松德凹印机组进行。以白卡纸套印电压作为参考,选取不同镜片组合进行生产打样。结果 镜片组合可以滤除镭射光柱,色标传感器能准确检测色标光信号,上机打样满足高精度多色套印,且不需要复杂的镂空、遮盖工艺,节省了一组色序,并节省了2%的承印物原材料。结论 对色标检测传感器检测原理的分析以及对镭射光柱纸的光谱反射率曲线的测量,实现了使用滤光镜片组合对镭射光柱的滤除,证明了套准标记可直接印刷在镭射光柱区域的可行性。同时,提高了承印物的利用率,减低了油墨使用量。     

Programmable color tuning of a multiline laser by means of a twisted nematic liquid crystal display

An optical system useful to tune in a controlled way the color of a triline argon krypton (Ar-Kr) laser by means of a twisted nematic liquid crystal display (TNLCD) is presented. The optical setup employs a 4f system and two blazed gratings to first separate and then recombine the spectrum of the light beam. The TNLCD is included in the intermediate focal plane operating in the amplitude modulation mode to control the relative transmission of each spectral line. The resulting color is accurately predicted by using a previously developed physical model of the spectral and voltage dependence of the TNLCD birefringence. By simply changing the gray level image addressed to the display, the Ar-Kr laser is color modulated at a video rate, thus becoming an interesting, reconfigurable, coherent light source for applications such as multicolor holography or color inspection.     

Fringe visibility improvement using an asynchronous image-subtracting optically addressed spatial light modulator

We demonstrate the application of an asynchronous image-subtraction optically addressed spatial light modulator to particle image velocimetry fringe processing. The device comprises an amorphous silicon p-i-n-i-p photosensor and a ferroelelectric liquid-crystal light-modulating layer. The images to be subtracted are encoded on two separate wavelengths. The operation of the device is described, and characterization shows a frame rate of 100 Hz, a resolution of 3 line pairs/mm, and a write-light sensitivity of ≈1 mW/cm(2) at a wavelength of 514 nm. The device is read by the use of light with a 633-nm wavelength whereas the subtraction light is at a wavelength of 670 nm. Using this device to subtract a nonuniform pedestal from the optically computed power spectral density function (the Young's fringe pattern), we find we can improve the signal-to-clutter ratio of peaks in the image-transmittance autocorrelation function of particle image velocimetry transparencies. The device also permits processing of very low-visibility fringe patterns, generated from doubly exposed images, in which one image has half the transmittance of the other. These could not be processed with a nonsubtracting, binary, liquid-crystal optically addressed spatial light modulator.