Stokes Parameter Images Research Articles

Polarization image demosaicing and RGB image enhancement for a color polarization sparse focal plane array.

The color division of focal plane (DoFP) polarization sensor structure mostly uses Bayer filter and polarization filter superimposed on each other, which makes the polarization imaging unsatisfactory in terms of photon transmission rate and information fidelity. In order to obtain high-resolution polarization images and high-quality RGB images simultaneously, we simulate a sparse division of focal plane polarization sensor structure, and seek a sweet spot of the simultaneous distribution of the Bayer filter and the polarization filters to obtain both high-resolution polarization images and high-quality RGB images. In addition, From the perspective of sparse polarization sensor imaging, leaving aside the traditional idea of polarization intensity interpolation, we propose a new sparse Stokes vector completion method, in which the network structure avoids the introduction and amplification of noise during polarization information acquisition by mapping the S1 and S2 components directly. The sparsely polarimetric image demosaicing (Sparse-PDM) model is a progressive combined structure of RGB image artifact removal enhancement network and sparsely polarimetric image completion network, which aims to compensate sparsely polarimetric Stokes parameter images with the de-artifacts RGB image as a guide, thus achieving high-quality polarization information and RGB image acquisition. Qualitative and quantitative experimental results on both self-constructed and publicly available datasets prove the superiority of our method over state-of-the-art methods.

Polarization Tomography with Stokes Parameters

We present a simple but powerful technique for the analysis of polarized emission from radio galaxies and other objects. It is based on the fact that images of Stokes parameters often contain considerably more information than is available in polarized intensity and angle maps. In general, however, the orientation of the Stokes parameters will not be matched to the position angles of structures in the source. Polarization tomography, the technique presented in this paper, consists of making a series of single linear Stokes parameter images, S(ρ), where each image is rotated by an angle ρ from the initial orientation of Q and U. Examination of these images, in a series of still frames or a movie, reveals often hidden patterns of polarization angles, as well as structures that were obscured by the presence of overlapping polarized emission. We provide both cartoon examples and a quick look at the complex polarized structure in Cygnus A.

Full Stokes single photon compressive polarization imaging.

We demonstrate a full Stokes polarization imaging system based on compressed sampling and single photon counting. The control and synchronization counting module based on field-programmable gate array is specially developed to control the rotation stage for polarization imaging at different directions. Additionally, it can load the binary random matrix into a digital micro-mirror device controller for each measurement and count the single photon pulse output from the photon counting photomultiplier tube simultaneously. The system can realize high-sensitivity single photon compressive imaging of the target under different polarization directions. On this basis, the high-quality Stokes parameter images and the angle of the linear polarization image can be obtained. The experimental results show that the polarization information can be reconstructed at a very low sampling ratio.

Single Pixel Compressive Spectral Polarization Imaging using a Movable Micro-Polarizer Array

The acquisition of spectral polarization images is a method that obtains polarized, spectral and spatial information of a scene. Traditional acquisition methods use dynamic elements that capture all the information of a scene, by scanning the areas of interest, which result in large amounts of data proportional to the desired image resolution. Hence, in this work, the compression of spectral polarization images using a single pixel architecture, that uses a micro-polarizer array aligned with a binary coded aperture is proposed. The micro-polarizer is moved horizontally in each shot, so that diverse types of codifications from the scene are obtained. The proposed architecture allows several compressive 2D projections with spatial, spectral and polarization coding to be obtained. Stokes parameter images at several wavelengths are reconstructed. This architecture reduces the total number of measurements needed to obtain spectral polarization images compared to traditional acquisition methods. The experiments validate the quality of the architecture obtaining 43.19 dB, 37.49 dB and 30.41 dB of the peak signal-to-noise ratio for the first three Stokes parameters respectively.

红外偏振成像系统高速处理模块设计

The high speed imaging processing module based on MWIR cooled 320256 detector, SDRAM memory and other function module circuit was designed for time-sharing type polarization imaging system. Processing module mainly included the driver board connected to detector, processing board with FPGA as its core, system power supply board. The algorithm of blind pixels compensation, nonuniformity correction, plateau histogram equalization and linear mapping were implemented, calibration parameters can be calculated online. Image processing module can realize the synchronization switch, integral time adjusted continuously, frame rate up to 200 fps, and output 320256 pixels high quality infrared image, meeting the requirement of the polarization imaging system to detect moving objects. Infrared polarization imaging experiments on plastic cups with groove were carried out, effective Stokes parameter images were extracted from the polarization images, and the significant polarization properties were observed. The processing module can be applied to the detection of space target, mine detection, maritime search and camouflage target detection.

Compressive spectral polarization imaging by a pixelized polarizer and colored patterned detector.

A compressive spectral and polarization imager based on a pixelized polarizer and colored patterned detector is presented. The proposed imager captures several dispersed compressive projections with spectral and polarization coding. Stokes parameter images at several wavelengths are reconstructed directly from 2D projections. Employing a pixelized polarizer and colored patterned detector enables compressive sensing over spatial, spectral, and polarization domains, reducing the total number of measurements. Compressive sensing codes are specially designed to enhance the peak signal-to-noise ratio in the reconstructed images. Experiments validate the architecture and reconstruction algorithms.

Stokes image reconstruction for two-color microgrid polarization imaging systems

The Air Force Research Laboratory has developed a new microgrid polarization imaging system capable of simultaneously reconstructing linear Stokes parameter images in two colors on a single focal plane array. In this paper, an effective method for extracting Stokes images is presented for this type of camera system. It is also shown that correlations between the color bands can be exploited to significantly increase overall spatial resolution. Test data is used to show the advantages of this approach over bilinear interpolation. The bounds (in terms of available reconstruction bandwidth) on image resolution are also provided.

Adaptive target detection with a polarization-sensitive optical system

We developed an adaptive polarimetric target detector (APTD) to determine the optimum combination strategy for a multichannel polarization-sensitive optical system. The proposed algorithm is based on scene-derived polarization properties of the target and background, and it seeks to find an optimum multichannel combination of linear polarizing filters that maximizes the signal-to-clutter ratio (SCR) in intensity and Stokes parameter images. The algorithm is validated by performing RX anomaly detection and a generalized likelihood ratio test on both synthetic and real imagery. The experimental results are analyzed through calculated SCR and receiver operating characteristic curves. Compared with several conventional operation methods, we find that better target detection performance is achieved with the APTD algorithm.

Optimizing imaging polarimeters constructed with imperfect optics

Imaging polarimeters are often designed and optimized by assuming that the polarization properties of the optics are nearly ideal. For example, we often assume that the linear polarizers have infinite extinction ratios. It is also usually assumed that the retarding elements have retardances that do not vary either spatially or with the angle of incidence. We consider the case where the polarization optics used to develop an imaging polarimeter are imperfect. Specifically, we examine the expected performance of a system as the extinction ratio of the diattenuators degrades, as the retardance varies spatially, and as the retardance varies with incidence angle. It is found that the penalty in the signal-to-noise ratio for using diattenuators with low extinction ratios is not severe, as an extinction ratio of 5 causes only a 2.0 dB increase in the noise in the reconstructed Stokes parameter images compared with an ideal diattenuator. Likewise, we find that a system can be optimized in the presence of spatially varying retardance, but that angular positioning error is far more important in rotating retarder imaging polarimeters.

Scattering coefficient determination in turbid media with backscattered polarized light

A simple empirical method is presented to determine the scattering coefficient mu' s from backscattered polarized images of turbid media. It uses the ratio, pixel by pixel, of two images that are the second and the first backscattered Stokes parameter images Q and I, respectively. Taking this image ratio, then integrating it over the azimuth angle, we get a function depending on the distance from the light entrance point. This function has a maximum. Using Monte Carlo simulations, for a fixed reduced scattering coefficient mu s and for an anisotropy factor g varying between 0 and 0.8, it is found a linear relationship between the scattering coefficient mu s and the inverse of the maximum position of this function.

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.

Design of optimal polarimeters: maximization of signal-to-noise ratio and minimization of systematic error.

The relationship between system condition and signal-to-noise ratio (SNR) in reconstructed Stokes parameter images is investigated for rotating compensator, variable retardance, and rotating analyzer Stokes vector (SV) polarimeters. A variety of optimal configurations are presented for each class of systems. The operation of polarimeters is discussed in terms of a four-dimensional conical vector space; and the concept of nonorthogonal bases, frames, and tight frames is introduced to describe the operation of SV polarimeters. Although SNR is an important consideration, performance of a polarimeter in the presence of errors in the calibration and alignment of the optical components is also important. The relationship between system condition and error performance is investigated, and it is shown that an optimum system from the point of view of SNR is not always an optimum system with respect to error performance. A detailed theory of error performance is presented, and the error of a SV polarimeter is shown to be related to the stability and condition number of the polarization processing matrices. The rms error is found to fall off as the inverse of the number of measurements taken. Finally, the concepts used to optimize SV polarimeters are extended to be useful for full Mueller matrix polarimeters.

Polarization sensitive optical coherence tomography of the rabbit eye

A polarization-sensitive optical coherence tomography (PSOCT) system was used to acquire depth-resolved images of the Stokes parameters of light backreflected from ex vivo rabbit eyes. The light backreflected from the eye interferes with that from the reference arm and is coherently detected in two orthogonal polarization channels. The two signals are digitized and the four Stokes parameters (I, Q, U, and V) of the backreflected light are computed for light backreflected from each longitudinal/lateral position in the eye. From the measured Stokes parameters, an estimate of the relative phase retardation between the two orthogonal polarizations can be determined. Two eyes were enucleated, imaged within 6-h postmortem and histology performed. Images of the Stokes parameters of light backreflected from the corneal stroma show significant local variations in the polarization state, possibly due to local changes in stromal structure. Depth-resolved Stokes parameter images of light backreflected from the retina were also acquired. A birefringent layer was observed at the position consistent with the known location of the nerve fiber layer (NFL). The local thickness of the birefringent layer determined with PSOCT was in good agreement with values determined histologically.