Alternative linear microgrid polarimeters: design, analysis, and demosaicing considerations

Abstract

Linear division of focal plane (DoFP), or integrated microgrid polarimeters, provide a measurement strategy for obtaining time-synchronized polarized intensity measurements across a scene. This is accomplished by masking pixels in the focal plane array sensor with a repeating pattern of different linear polarizers. The convention in industry has been to use a repeating 2 × 2 pattern of four linear polarizers with chosen polarizer orientation angles of { 0 , 45 , 90 , 135 } ∘ . Alternative designs based upon other P × Q modulation patterns have been proposed that demonstrate improved performance over conventional microgrid arrays due to better utilization of bandwidth in the frequency domain. Here, we develop a model for linear DoFP snapshot polarimeters that provides an in-depth understanding of these devices in both the spatial and frequency domains and relate this model to previously reported generalized DoFP channeled polarimeter models. We then use the model to identify practical modulation patterns and study their performance through empirical simulations based upon data collected from real polarimeters. We demonstrate the validity of the developed model and compare the performance of the identified modulation schemes against a common set of ground truth images. We find that choosing alternative sets of polarizer angles, in conjunction with modulators that improve bandwidth usage, result in the best overall designs that can improve performance over conventional microgrid polarimeters.

A new adaptive window‐based guided filtering and interpolation for polarization image demosaicing

“…Therefore, ∇ 2 (S 0 M n )is the masked approximate Laplacian map of S0. As shown in (18), the difference betweenI sub n and Ĩn is elementarily multiplied with M n . The mask M n multiplies only at those pixels with available ground truth in I sub n (i.e.…”

“…By ( 18), ( 20) and ( 21), we use all four candidate window scales to generate four sets of candidate variables, which are denoted as {a r1 n (p, q), b r1 n (p, q), LE r1 n (p, q)}, {a r2 n (p, q), b r2 n (p, q), LE r2 n (p, q)}, {a r3 n (p, q), b r3 n (p, q), LE r3 n (p, q)}and{a r4 n (p, q), b r4 n (p, q), LE r4 n (p, q)}. It should be noted that the target image and guide image in (18), (20) and ( 21) remain unchanged. Next, we select the minimum local estimation error at each pixel, as…”

“…In the past few decades, several types of polarization imaging methods were proposed including division of time, division of amplitude, division of aperture and division of focal plane (DoFP) [15][16][17][18][19]. DoFP becomes the main-stream due to its integrated sampling structure and high frame rate.…”

A laboratory-aided empirically driven polarimetric bidirectional reflectance distribution function model

“…With all geometry transformations applied, we shift our focus to the image data. For each collected target orientation, we first apply a Fourier domain demosaicing strategy by Ratliff et al 10 to obtain the full resolution polarized intensity image for each polarizer channel. We then compute the Stokes vector, DoLP, and AoP using Eqs.…”

Sub-percent characterization and polarimetric performance analysis of commercial micro-polarizer array detectors

“…44 Over the years, even more intricate patterns have been developed to increase the bandwidth and improve accuracy. [45][46][47] The RGB versions of the Sony detector are manufactured using a (2×2)×(2×2) repeating superpixel pattern of 4×4, while also for such configurations more optimal combined color/polarization solutions can be found. 48 In this work, we have focused our efforts on mitigating the detector effects that intrinsically limit the polarimetric accuracy at fractional polarization levels of ∼1% (or worse), and, through rigorous calibration, achieve a sub-percent polarimetric accuracy.…”