Multifusion, Multispectral, Optical Polarimetric Imaging Sensing Principles

The goal of this study is to present novel, multifusion optical imaging sensing principles, based on active-multispectral polarimetric imaging of targets surrounded by scattered media. Specifically, the novelty of this study consists in the fusion of multispectral images, with polarimetric imaging principles, forming image differences. The experimental results indicate clearly that, high-contrast multispectral Mueller polarimetric image differences, as well as Degree of Linear Polarization (DOLP) images can be obtained from transmitted or backscattered photons, from targets embedded in turbid media.     

Imaging multispectral polarimetric sensor: single-pixel design,fabrication, and characterization

A discrete-component approach was taken to establish the operational feasibility of a novel, imaging, midinfrared, multispectral, polarimetric sensor for remote-sensing application. The sensor is designed to exploit the spectral and polarimetric characteristics of the scene as discriminants. Pixelated multispectral filters and polarization filters were designed and fabricated on sapphire and Si substrates, respectively, and both were characterized. A single-pixel spectropolarimetric composite filter was characterized by use of a Fourier transform infrared spectrometer and a Pt-Si thermal-imaging camera. The experimental results show excellent agreement with theoretical predictions.     

Target detection with a liquid-crystal-based passive Stokes polarimeter

We present an imaging system that measures the polarimetric state of the light coming from each point of a scene. This system, which determines the four components of the Stokes vector at each spatial location, is based on a liquid-crystal polarization modulator, which makes it possible to acquire four-dimensional Stokes parameter images at a standard video rate. We show that using such polarimetric images instead of simple intensity images can improve target detection and segmentation performance.     

Clustering of polarization-encoded images

Polarization-encoded imaging consists of the distributed measurements of polarization parameters for each pixel of an image. We address clustering of multidimensional polarization-encoded images. The spatial coherence of polarization information is considered. Two methods of analysis are proposed: polarization contrast enhancement and a more-sophisticated image-processing algorithm based on a Markovian model. The proposed algorithms are applied and validated with two different Mueller images acquired by a fully polarimetric imaging system.     

When is polarimetric imaging preferable to intensity imaging for target detection?

We consider target detection in images perturbed with additive noise. We determine the conditions in which polarimetric imaging, which consists of analyzing of the polarization of the light scattered by the scene before forming the image, yields better performance than classical intensity imaging. These results give important information to assess the interest of polarimetric imaging in a given application.     

High-resolution underwater acoustic imaging with lens-based systems

In recent years, several sonars designed for high-resolution, short-range underwater imaging have been developed. These imaging systems use an acoustic lens to focus the incoming waves on an array of transducers. In this article we describe three prototype systems that use a line-focus or a point-focus lens and operate at a frequency of 300 kHz or 3 MHz. The line-focus lens produces two-dimensional (2D) intensity images, while the point-focus lens produces 3D intensity images. We present sample images taken from moving and stationary platforms, and discuss the techniques used for processing the acoustic backscatter data to reconstruct and visualize the scene. The images, particularly those taken with a point-focus lens, show a remarkable degree of detail. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 377–385, 1997     

Digital three-dimensional image correlation by use of computer-reconstructed integral imaging

We use integral images of a three-dimensional (3D) scene to estimate the longitudinal depth of multiple objects present in the scene. With this information, we digitally reconstruct the objects in three dimensions and compute 3D correlations of input objects. We investigate the use of nonlinear techniques for 3D correlations. We present experimental results for 3D reconstruction and correlation of 3D objects. We demonstrate that it is possible to perform 3D segmentation of 3D objects in a scene. We finally present experiments to demonstrate that the 3D correlation is more discriminant than the two-dimensional correlation.     

3D photon counting integral imaging with unknown sensor positions

Photon counting techniques have been introduced with integral imaging for three-dimensional (3D) imaging applications. The previous reports in this area assumed a priori knowledge of exact sensor positions for 3D image reconstruction, which may be difficult to satisfy in certain applications. In this paper, we extend the photon counting 3D imaging system to situations where sensor positions are unknown. To estimate sensor positions in photon counting integral imaging, scene details of photon counting images are needed for image correspondences matching. Therefore, an iterative method based on the total variation maximum a posteriori expectation maximization (MAP-EM) algorithm is used to restore photon counting images. Experimental results are presented to show the feasibility of the method. To the best of our knowledge, this is the first report on 3D photon counting integral imaging with unknown sensor positions.     

Enhanced three-dimensional integral imaging system by use of double display devices

We propose an enhanced three-dimensional (3D) integral imaging system using multiple display devices. Experimental results with double devices prove the improvement in the image depth for a given image quality. We present experiments on an enhanced 3D integral imaging system using double display devices, in which two 3D subimages that cover different depth ranges are separately generated in each device, and then they are combined with a beam splitter to reconstruct the whole 3D image with an enhanced depth of view. In a similar manner, the double-device system can also be used to obtain a wider viewing angle by combining two images with different viewing angle ranges. We discuss the possibility of 3D integral imaging systems using multiple display devices as extensions of the system with double display devices.     

Multifusion Multispectral Lightwave Polarimetric Detection Principles and Systems

The objective of this paper is to present novel detection principles based on all active multispectral polarimetric subtraction imaging principles of targets embedded in scattering media. The novelty of this contribution consists in the formation of multispectral Stokes' parameter image differences, degree of linear polarization image differences, and Mueller-matrix image differences. As a result, high-contrast high-specificity images can be obtained by removing the background from the target. Further contrast enhancement of the target with light beam steering capabilities can be obtained by doping the background surrounding the target or the target itself with high-index-of-refraction polar molecules/nanoparticles. The presented optical principles can be successfully applied to a variety of applications, such as cancer detection and treatment, molecular imaging, and development of photonics and nanophotonic devices, for a widespread group of applications, such as defense and advanced medical diagnostic and analytical devices     

基于各向异性二维Ge Se的无偏振器偏振图像传感器

偏振是光的一个重要信息,偏振探测可以把信息量从三维(光强、光谱和空间)扩充到七维(光强、光谱、空间、偏振度、光偏振等),为成像物体提供关键的视觉信息(如表面粗糙度、几何形状或方向),因此偏振成像技术在目标检测等领域有着巨大的潜力.然而这些领域往往需要复杂的偏振编码,现有的复杂透镜系统和偏振器限制了集成成像传感器的小型化能力.本文通过二维各向异性α-Ge Se半导体,成功实现了无偏振器的偏振敏感可见-近红外光电探测器/成像仪.作为传感器系统的关键部件,该原型Au/GeSe/Au光电探测器具有灵敏度高、光谱响应宽、响应速度快(~10³A W^-1, 400–1050 nm, 22.7/49.5μs)等优点.此外,该器件在690–1050 nm光谱范围内表现出独特的偏振灵敏度,并且对沿y方向的偏振光吸收最强,这一点通过分析α-Ge Se的光跃迁行为也得到了证实.最后,将2D-Ge Se器件应用到成像系统中进行偏振成像,在808 nm近红外波段处,在不同的偏振方向上,辐射目标的对比度为3.45.这种成像仪在没有偏振器的情况下,能够在场景中感知双频偏振信号,为偏振成像传感器阵列的广泛应用奠定了基础.     

An Internet-enabled image- and model-based virtual machining system

Virtual reality (VR) can be described as a four-dimensional (4-D) simulation of the real world, including the 3-D geometry space, 1-D time and the immersive or semi-immersive interaction interface. VR applications in mechanical-related research areas are becoming popular, e.g. virtual layout design, virtual prototyping, Internet-based virtual manufacturing, etc. However, research in VR applications is facing conflicting requirements for high rendering quality and near real-time interactivity. This paper represents an Internet-based virtual machining system that builds an integrated VR scene, which combines images and models, to overcome the above conflicts. This research is divided into three parts: first, image mosaics techniques are used to implement an Internet-based virtual workshop, which is an image-based virtual scene. The method of obtaining original sequential images, the principle of image mosaics to realize automatic seamless stitching, and projection transformation matrices to reconstruct a closed inward-facing space are presented. Secondly, a model-based virtual milling machine has been constructed with three detailed approaches: a category-based dynamic graph structure to support collision detection, a relation-oriented collision detection method to improve the efficiency of collision detection, and a dynamic modelling method to model a dynamic workpiece object. Finally, an Internet-based virtual milling system, which is the integration of the image-based virtual workshop and the model-based virtual CNC machine, is constructed using the reposition method to achieve visual consistency of the virtual objects and images. This system, which includes an integrated scene, combines the advantages of image-based VR and model-based VR. Consequently, this system has both high rendering quality and good real-time interactivity.     

Design and fabrication of a low-cost, multispectral imaging system

This paper reports the design and construction of a low-cost, multispectral imaging system using a single, large format CCD and an array of 18 individual lenses coupled to individual spectral filters. The system allows the simultaneous acquisition of 18 subimages, each with potentially different optical information. The subimages are combined to create a composite image, highlighting the desired spectral information. Because all the subimages are acquired simultaneously, the composite image shows no motion artifact. Although the present configuration uses 17 narrow bandpass optical filters to obtain multispectral information from a scene, the system is designed to be a general purpose, multiaperture platform, easily reconfigured for other multiaperture imaging modes.     

Parametric estimation of the square degree of polarization from two intensity images degraded by fully developed speckle noise

Active polarimetric imagery systems allow one to reveal polarimetric characteristics of the scene. Among them, the degree of polarization allows one to have information about the polarizing nature of an imaged object. Its estimation is standardly done from four images of the scene. Reducing this number of images can be of great interest for industrial applications, allowing in particular reduction of cost in terms of money and acquisition time. We propose a parametric method to estimate the square degree of polarization from only two measurements when coherent illumination is considered and when the images are corrupted with fully developed speckle, and we characterize the performances of the estimation.     

Generic camera model and its calibration for computational integral imaging and 3D reconstruction

Integral imaging (II) is an important 3D imaging technology. To reconstruct 3D information of the viewed objects, modeling and calibrating the optical pickup process of II are necessary. This work focuses on the modeling and calibration of an II system consisting of a lenslet array, an imaging lens, and a charge-coupled device camera. Most existing work on such systems assumes a pinhole array model (PAM). In this work, we explore a generic camera model that accommodates more generality. This model is an empirical model based on measurements, and we constructed a setup for its calibration. Experimental results show a significant difference between the generic camera model and the PAM. Images of planar patterns and 3D objects were computationally reconstructed with the generic camera model. Compared with the images reconstructed using the PAM, the images present higher fidelity and preserve more high spatial frequency components. To the best of our knowledge, this is the first attempt in applying a generic camera model to an II system.     

Photon-counting three-dimensional integral imaging with compression of elemental images

In this paper, we present lossless compression of elemental images in photon-counting integral imaging. In order to verify the performance of the compression method applied to low light level three-dimensional (3D) integral imaging, we compute the correlation coefficient and peak to mean square error (PSNR) as metrics for 3D scene reconstruction integrity. We show quantitatively via experiments that a considerable compression of the elemental images in photon-counting integral imaging may be achievable without significant loss in the performance in terms of correlation and PSNR metrics. To the best of our knowledge, this is the first report on applying lossless compression algorithms in photon-counting 3D computational integral imaging.     

Multispectral polarization imaging for observing blood oxygen saturation in skin tissue

We propose a new technique that combines two-dimensional (2D) multispectral imaging and polarization gating for observing the blood oxygen saturation (SpO2) level in human skin tissue. The spectral decomposition of the skin tissue image provides the principal information on blood oxygenation. The polarization gating selects the measurement depth according to the relative orientation of the two polarizers that are placed on a camera and a light source. The combination of these two methods yields multispectral images of the superficial and deep layers of the skin tissue separately. In order to evaluate the blood oxygen, we focus on the multispectral images of the deep site. The SpO2 levels at each image pixel are calculated by means of the partial least squares regression with respect to each reflectance spectrum. The reassignment of the predicted responses retrieves an image whose pixel values represent the relative SpO2 levels. A demonstration experiment for acquiring the multispectral polarization images is performed in the spectral range of 500 to 680 nm, and the SpO2 distributions are obtained.     

Spaceborne imaging radars

The Seasat and Shuttle imaging radars flown in the 1970s and 1980s established a strong scientific and technical base for a number of imaging radars that are flying or under development. Recent advances in understanding wave-surface interactions, utilization of multispectral and polarimetric data, as well as advances in microwave and electronic technology, are allowing the development of a new generation of multiparameter imaging radars that will allow quantitative measurements of surface and near-surface geophysical parameters and monitoring of surface processes over long-term duration. This article is an overview of spaceborne imaging radars presently flying or under development.     

Markov-based methodology for the restoration of underwater acoustic images

This article describes a probabilistic technique for the restoration of underwater acoustic images that is based on the Markov random fields (MRFs) methodology. The beamforming is applied to rough acoustic data that derive from multibeam systems or acoustic cameras to build a three-dimensional (3D) map, that is associated point by point with the estimates of the reliability of such measures. Specifically, backscattered echoes that are received by a 2D array antenna are arranged to generate two images in which each pixel represents the distance (range) from the sensor plane and the confidence of the measures, respectively. Unfortunately, this kind of image is affected by several problems due to the nature of the signal and the related sensing system. In the proposed algorithm, the range and the confidence images are modeled as separate MRFs whose associated probability distributions embed knowledge of the acoustic system, of the considered scene, and of the noise affecting the measures. In particular, the confidence image is first restored and the result is used to reconstruct the 3D image to allow an active integration of the reliability information. Optimal (in the maximum a posteriori probability sense) estimates of the reconstructed 3D map and the restored confidence image are obtained by minimizing the energy functionals, using simulated annealing. Experimental results on synthetic and real images show the performance of the proposed approach. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 386–395, 1997     

Target segmentation in active polarimetric images by use of statistical active contours

We address the problem of target segmentation in active polarimetric images, which can reveal contrasts that do not appear in standard intensity images. However, these images are perturbed by strong specklelike noise. For the purpose of segmentation we thus use statistical active contours, which are known to possess noise robustness properties. The polarimetric imagers we consider acquire two different images of the same scene so as to form a two-channel image (TCI). These two images can be combined to form the orthogonal state contrast image (OSCI), which represents the degree of polarization of the backscattered light if its coherency matrix is diagonal. We characterize the segmentation performance of the statistical active contour procedure on the TCI and on the OSCI. In particular, we show that if the illumination beam is spatially nonuniform, it is more efficient to perform the segmentation on the OSCI, which is independent of the spatial variations of the illumination.