scholarly journals Polarized Light Field Imaging for Single-Shot Reflectance Separation

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3803 ◽  
Author(s):  
Jaewon Kim ◽  
Abhijeet Ghosh
Keyword(s):  
Light Field ◽  
Polarized Light ◽  
Angular Separation ◽  
Single Scattering ◽  
Computational Photography ◽  
Single Shot ◽  
Specular Reflectance ◽  
Structured Lighting ◽  
Separation Results ◽  
Imaging Conditions

We present a novel computational photography technique for single-shot separation of diffuse/specular reflectance, as well as novel angular domain separation of layered reflectance. We present two imaging solutions for this purpose: two-way polarized light-field (TPLF) imaging and four-way polarized light-field (FPLF) imaging. TPLF imaging consists of a polarized light-field camera, which simultaneously captures two orthogonal states of polarization. A single photograph of a subject acquired with the TPLF camera under polarized illumination then enables standard separation of diffuse (depolarizing) and polarization preserving specular reflectance using light-field sampling. We further demonstrate that the acquired data also enable novel angular separation of layered reflectance including separation of specular reflectance and single scattering in the polarization preserving component, as well as separation of shallow scattering from deep scattering in the depolarizing component. FPLF imaging further generalized the functionality of TPLF imaging under uncontrolled unpolarized or partially polarized illumination such as outdoors. We apply our approach for efficient acquisition of facial reflectance including diffuse and specular normal maps and novel separation of photometric normals into layered reflectance normals for layered facial renderings. We validate our proposed single-shot layered reflectance separation under various imaging conditions and demonstrate it to be comparable to an existing multi-shot technique that relies on structured lighting while achieving separation results under a variety of illumination conditions.

Steady state of atoms in a monochromatic elliptically polarized light field

1998 ◽  
Vol 44 (1) ◽  
pp. 20-24 ◽  
Author(s):  
G Nienhuis ◽  
A. V Taichenachev ◽  
A. M Tumaikin ◽  
V. I Yudin
Keyword(s):  
Steady State ◽  
Light Field ◽  
Polarized Light ◽  
Elliptically Polarized Light ◽  
Elliptically Polarized

scholarly journals Vari-Focal Light Field Camera for Extended Depth of Field

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1453
Author(s):  
Hyun Myung Kim ◽  
Min Seok Kim ◽  
Sehui Chang ◽  
Jiseong Jeong ◽  
Hae-Gon Jeon ◽  
...  
Keyword(s):  
Light Field ◽  
High Reliability ◽  
Focal Length ◽  
Outdoor Environment ◽  
Depth Of Field ◽  
Depth Information ◽  
Single Shot ◽  
Depth Sensing ◽  
Depth Measurement ◽  
Sensing Applications

The light field camera provides a robust way to capture both spatial and angular information within a single shot. One of its important applications is in 3D depth sensing, which can extract depth information from the acquired scene. However, conventional light field cameras suffer from shallow depth of field (DoF). Here, a vari-focal light field camera (VF-LFC) with an extended DoF is newly proposed for mid-range 3D depth sensing applications. As a main lens of the system, a vari-focal lens with four different focal lengths is adopted to extend the DoF up to ~15 m. The focal length of the micro-lens array (MLA) is optimized by considering the DoF both in the image plane and in the object plane for each focal length. By dividing measurement regions with each focal length, depth estimation with high reliability is available within the entire DoF. The proposed VF-LFC is evaluated by the disparity data extracted from images with different distances. Moreover, the depth measurement in an outdoor environment demonstrates that our VF-LFC could be applied in various fields such as delivery robots, autonomous vehicles, and remote sensing drones.

Microphotometry of Underwater Shadowing by a Moss from a Niagara Escarpment Waterfall

2010 ◽  
Vol 17 (1) ◽  
pp. 125-131
Author(s):  
Howard J. Swatland
Keyword(s):  
Point Source ◽  
Single Cells ◽  
Incident Light ◽  
Polarized Light ◽  
Specular Reflectance ◽  
Light Spectra ◽  
Niagara Escarpment ◽  
Single Leaf ◽  
Diffuse Illumination ◽  
Air Water Interface

AbstractMicroscope and fiber-optic spectrophotometry of transmittance and backscattering both showed moss leaves to be capable of casting strong shadows, with a single leaf blocking approximately 90% of incident light from a point source. In leaves with only one layer of cells, the transmittance through the cytoplasm of single cells was similar to that for whole leaves. Analysis of cell wall birefringence by polarized-light interferometry indicated that cell walls might normally scatter rather than transmit light. Spectra transmitted through, or backscattered from, the upper green layers of moss were dominated by selective absorbance from chlorophyll, but there was also evidence of wavelength-dependent scattering, as detected in the lower layers of brown, dead moss. Specular reflectance from moss leaves was detected by polarimetry and may have contributed to the relatively high macroscopic transmittance of stationary moss in water. Shadowing by moss leaves was confirmed by dynamic measurements of mosses in turbulent water without bubbles. Flicker patterns from leaves were superimposed on the underwater flicker pattern created at the air-water interface, thus flecks of light were reduced in intensity, increased in frequency, and decreased in duration. This was detected with both point source and diffuse illumination of samples.

Polarization

2011 ◽  
Author(s):  
Sönke Johnsen
Keyword(s):  
Polarized Light ◽  
Coherent Scattering ◽  
Single Scattering ◽  
The Other ◽  
Butterfly Wings

This chapter examines polarization. As with radiometry, polarization can be a confusing topic. Unfortunately, unlike radiometry, its complexity is not primarily due to confusing units. The physics of polarized light is genuinely tricky. This is another subfield of optics that is made easier by thinking of light as a wave. Polarized light in nature is a scattering phenomenon. However, not all scattering is equally effective at polarizing light. Two kinds work best. The first is single scattering by particles much smaller than a wavelength of light. The other way in which scattering can create polarized light is via coherent scattering—in particular, reflection from smooth substances such as glass, water, and many leaves or structurally colored objects like iridescent butterfly wings.

scholarly journals Robust Depth Estimation for Light Field Microscopy

Sensors ◽  
2019 ◽  
Vol 19 (3) ◽  
pp. 500 ◽  
Author(s):  
Luca Palmieri ◽  
Gabriele Scrofani ◽  
Nicolò Incardona ◽  
Genaro Saavedra ◽  
Manuel Martínez-Corral ◽  
...  
Keyword(s):  
Light Field ◽  
Three Dimensional ◽  
Depth Map ◽  
Depth Estimation ◽  
Fourier Integral ◽  
Single Shot ◽  
Natural Scene ◽  
Multi Scale ◽  
Depth Maps ◽  
New Applications

Light field technologies have seen a rise in recent years and microscopy is a field where such technology has had a deep impact. The possibility to provide spatial and angular information at the same time and in a single shot brings several advantages and allows for new applications. A common goal in these applications is the calculation of a depth map to reconstruct the three-dimensional geometry of the scene. Many approaches are applicable, but most of them cannot achieve high accuracy because of the nature of such images: biological samples are usually poor in features and do not exhibit sharp colors like natural scene. Due to such conditions, standard approaches result in noisy depth maps. In this work, a robust approach is proposed where accurate depth maps can be produced exploiting the information recorded in the light field, in particular, images produced with Fourier integral Microscope. The proposed approach can be divided into three main parts. Initially, it creates two cost volumes using different focal cues, namely correspondences and defocus. Secondly, it applies filtering methods that exploit multi-scale and super-pixels cost aggregation to reduce noise and enhance the accuracy. Finally, it merges the two cost volumes and extracts a depth map through multi-label optimization.

A polarized light field microscope with fast polarization switcher and microlens array reveals the 3-D birefringence distribution of complex anisotropic structures

2008 ◽  
Vol 14 (S2) ◽  
pp. 742-743
Author(s):  
R Oldenbourg
Keyword(s):  
New Mexico ◽  
Light Field ◽  
Polarized Light ◽  
Microlens Array ◽  
Anisotropic Structures ◽  
Fast Polarization

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

s- and p-Polarized Infrared Specular Reflectance of Vitreous Silica at Oblique Incidences: Detection of LO Modes

2000 ◽  
Vol 54 (4) ◽  
pp. 502-507 ◽  
Author(s):  
B. C. Trasferetti ◽  
C. U. Davanzo
Keyword(s):  
High Frequency ◽  
Incidence Angle ◽  
Polarized Light ◽  
Blue Shift ◽  
Refraction Index ◽  
Vitreous Silica ◽  
Reflectance Spectra ◽  
Specular Reflectance ◽  
Longitudinal Optic ◽  
Asymmetrical Mode

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.

Solar Concentrator Shape Characterisation Using Composite Light-Field Imaging

2015 ◽  
Author(s):  
Oliver Garbrecht ◽  
José Zapata ◽  
Reinhold Kneer
Keyword(s):  
Light Field ◽  
Single Point ◽  
Single Shot ◽  
Solar Concentrator ◽  
Original Design ◽  
Entire Surface ◽  
Manufacturing Defects ◽  
Wide Range ◽  
Light Field Imaging ◽  
Field Imaging

The shape of an installed solar concentrator (e.g. a heliostat) may differ from its original design due to manufacturing defects, structural/wind loads and thermal expansion. By measuring the shape of a solar concentrator, it is possible to account for the deviation in optical performance from its original design point. A method to measure concentrator shape needs to be fast, accurate, and not involve contact or interference with the reflective surface of the concentrator. State-of-the-art techniques include flux mapping, photogrammetry, and deflectometry using conventional cameras. This paper presents a study to characterise solar concentrator shapes using light-field imaging. Conventional cameras capture the light intensity of a point in a scene at a single point in the sensor, creating a two-dimensional image. A light field camera features multiple micro-lenses placed between the main lens and the sensor, providing many small images from slightly different angles in a single shot. This information is used to reconstruct the position of a light source in space. The advantage of this new technique to the ones mentioned above is that the light field camera is robust and self-contained, which allows easy-to-use application in heliostat fields. In this study, light-field camera measurements were performed with flat mirrors and a curved mirror under laboratory conditions. In order to resolve the surface of the mirror surfaces, several methods to impose contours of the mirror surface have been studied, including dirt, small water droplets, scattering of low-power laser light, and paper-marks. A wide range of camera-to-mirror distances between 43 cm and 5 m have been studied. Greater distances allow the capture of the entire surface, but decrease the precision of depth measurements. In order to obtain high precision measurements while being able to capture the entire surface, a compositing strategy has been developed, combining several light-field image measurements. The overall accuracy of the system was improved further by averaging measurements over several image frames. Subsequently, the reconstructed surface points have been fed to a ray-tracing algorithm realized in Matlab/Python. Results in this study are able to resolve the shape of small concentrators to sub-millimetre precision when taking pictures at a distance of 0.4 m.

scholarly journals Observation of non-principal plane neutral points in the in-water upwelling polarized light field

2011 ◽  
Vol 19 (7) ◽  
pp. 5942 ◽  
Author(s):  
Kenneth J. Voss ◽  
Arthur C. R. Gleason ◽  
Howard R. Gordon ◽  
George W. Kattawar ◽  
Yu You
Keyword(s):  
Light Field ◽  
Polarized Light ◽  
Principal Plane
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