Minimized Laplacian residual interpolation for DoFP polarization image demosaicking

Single-shot 3 × 3 Mueller matrix microscopy with color polarization encoding

Snapshot retrieval of linear Stokes parameters in polarized light microscopy has benefited from recent advances in nanotechnology which have made polarization image sensors commercially available. However, real-time retrieval of the 3 × 3 Mueller matrix (MM) is limited by the need for time-sequential change in polarization states in the input. In the present Letter, we propose a cost-effective technique for the real-time retrieval of the 3 × 3 Mueller matrix by encoding linear polarization states in each of the three color channels of the source and analyzing light passing through the sample using a color polarization sensor placed in the imaging plane of a transmission microscope. Validation experiments for samples under real-time imaging conditions are presented. To the best of our knowledge, this is the first report on the snapshot 3 × 3 Mueller matrix element retrieval in polarized light microscopy by combining division of focal plane (DoFP) color polarimetric sensing and polarization color encoding of the source.

Modified Newton-residual interpolation for division of focal plane polarization image demosaicking

With the improvement of semiconductor processing technology, polarization sensors using division of focal plane have gradually become the mainstream method of polarization imaging. Similar to the color restoration method of the Bayer array sensor, the spatial information of polarized image is also recovered through the polarization demosaicking algorithm. In this paper, we propose a new modified Newton-residual interpolation polarization image demosaicking algorithm based on residual interpolation, which is suitable for a monochrome or color polarization filter array. First, we use the modified Newton interpolation method to generate edge-sensitive guiding images. Then, we carry out the improvement of the guide process during the residual interpolation by performing variance statistics on the local window image in the guiding process, so that the edges and flat image blocks have different guiding weights. Finally, we obtain edge-preserving results by applying these two improvements, which reduces the zipper effect and edge confusion. We compare the results of various algorithms on experimental data, demonstrating that our algorithm has impactful improvements in the evaluation metrics based on the ground-truth images.

Polarized Intensity Ratio Constraint Demosaicing for the Division of a Focal-Plane Polarimetric Image

Polarization is an independent dimension of light wave information that has broad application prospects in machine vision and remote sensing tasks. Polarization imaging using a division-of-focal-plane (DoFP) polarimetric sensor can meet lightweight and real-time application requirements. Similar to Bayer filter-based color imaging, demosaicing is a basic and important processing step in DoFP polarization imaging. Due to the differences in the physical properties of polarization and the color of light waves, the widely studied color demosaicing method cannot be directly applied to polarization demosaicing. We propose a polarized intensity ratio constraint demosaicing model to efficiently account for the characteristics of polarization detection in this work. First, we discuss the special constraint relationship between the polarization channels. It can be simply described as: for a beam of light, the sum of the intensities detected by any two vertical ideal analyzers should be equal to the total light intensity. Then, based on this constraint relationship and drawing on the concept of guided filtering, a new polarization demosaicing method is developed. A method to directly use raw images captured by the DoFP detector as the ground truth for comparison experiments is then constructed to aid in the convenient collection of experimental data and extensive image scenarios. Results of both qualitative and quantitative experiments illustrate that our method is an effective and practical method to faithfully recover the full polarization information of each pixel from a single mosaic input image.

Snapshot polarimetric imaging in multi-view microscopy

Polarimetric imaging allows for the vector nature of optical information across a scene to be obtained, with recent applications ranging from remote sensing to microscopy. In polarimetric microscopy in particular, different polarization states are conventionally achieved under time-division multiplexing strategies and are mainly subject to static phenomena. In the present work, we propose a cost-effective technique for polarization sensing with the possibility of real-time imaging microscopy. By modifying a commercial camera and replacing the conventional lens with an optical system that integrates a microscope objective and a lenslet array with a polarization mask, linear Stokes parameters can be obtained in a snapshot. The proposed scheme is robust against misalignment and suitable for handling video sequences of microscopic samples. To the best of our knowledge, this is the first report on combining multi-view sensing and polarization imaging for applications to microscopy.

Residual Interpolation Integrated Pixel-by-Pixel Adaptive Iterative Process for Division of Focal Plane Polarimeters

Residual interpolations are effective methods to reduce the instantaneous field-of-view error of division of focal plane (DoFP) polarimeters. However, their guide-image selection strategies are improper, and do not consider the DoFP polarimeters’ spatial sampling modes. Thus, we propose a residual interpolation method with a new guide-image selection strategy based on the spatial layout of the pixeled polarizer array to improve the sampling rate of the guide image. The interpolation performance is also improved by the proposed pixel-by-pixel, adaptive iterative process and the weighted average fusion of the results of the minimized residual and minimized Laplacian energy guide filters. Visual and objective evaluations demonstrate the proposed method’s superiority to the existing state-of-the-art methods. The proposed method proves that considering the spatial layout of the pixeled polarizer array on the physical level is vital to improving the performance of interpolation methods for DoFP polarimeters.

Polarization-Sensitive and Wide Incidence Angle-Insensitive Fabry-Perot Optical Cavity Bounded by Two Metal Grating Layers

Infrared (IR) polarimetric imaging has attracted attention as a promising technology in many fields. Generally, superpixels consisting of linear polarizer elements at different angles plus IR imaging array are used to obtain the polarized target signature by using the detected polarization-sensitive intensities. However, the spatial arrangement of superpixels across the imaging array may lead to an incorrect polarimetric signature of a target, due to the range of angles from which the incident radiation can be collected by the detector. In this article, we demonstrate the effect of the incident angle on the polarization performance of an alternative structure where a dielectric layer is inserted between the nanoimprinted subwavelength grating layers. The well-designed spacer creates the Fabry–Perot cavity resonance, and thereby, the intensity of transverse-magnetic I-polarized light transmitted through two metal grating layers is increased as compared with a single-layer metal grating, whereas transverse-electric (TE)-transmitted light intensity is decreased. TM-transmittance and polarization extinction ratio (PER) of normally incident light of wavelength 4.5 μm are obtained with 0.49 and 132, respectively, as the performance of the stacked subwavelength gratings. The relative change of the PERs for nanoimprint-lithographically fabricated double-layer grating samples that are less than 6% at an angle of incidence up to 25°, as compared to the normal incidence. Our work can pave the way for practical and efficient polarization-sensitive elements, which are useful for many IR polarimetric imaging applications.