Accepted papers to appear in an upcoming issue
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Color Brightness Model and Its Imaging Applications
Ying-Yi Li and Hsien-Che Lee
Doc ID: 351388 Received 08 Nov 2018; Accepted 17 Jan 2019; Posted 17 Jan 2019 View: PDF
Abstract: We have developed an empirical umbrella model for predicting the brightness of colors. It is based on amodified concept of radiance factor. Instead of a single reference white for all colors, each color has itsown reference color. Our model shows that for near neutral colors, the boundary of the object-color solidaccounts for most of the hue angles, except in the cyan-blue region where the boundary has to be adjustedby experiments on color charts. We use an exponential function to extrapolate the umbrella to the colorsof higher purity. The model is used to adjust the luminance of the Munsell colors to make them equallybright by compensating for the Helmholtz-Kohlrausch effect. It is also applied to real consumer imagesto reduce their brightness after boosting their color saturation. For both applications, the comparisonimages show that the model is quite effective.
Predicting the performance of low-cost colorinstruments for color identification
Eric Kirchner, Pim Koeckhoven, and Keshav Sivakumar
Doc ID: 351632 Received 12 Nov 2018; Accepted 17 Jan 2019; Posted 17 Jan 2019 View: PDF
Abstract: During the past few years, several instruments for color measurement have become commercially available atunprecedented low prices. Although these instruments are no spectrophotometers, their price-performance ratiomay be attractive for applications which do not require the high accuracy of traditional instruments.We investigated the performance of this class of instruments. These instruments typically do not provide spectralreflectance data, and some do not even produce colorimetric data such as CIELab coordinates. Therefore, in thisinvestigation we express performance of the devices as the percentage of correctly identified color chips in colordocumentations (fan decks) such as those from RAL and Dulux CP5. Based on statistical physics we develop amathematical model that predicts the performance of a low-cost color instrument. This performance is shown todepend mainly on (i) the measurement precision of the instrument, and on (ii) the density of chip color coordinatesin the color documentation. The new model makes it possible to compare test results from different instruments,even if they were obtained with different color documentations. The model can also be used to help designing anefficient quality control test for the instruments, and to design new color documentations for which the instrumentgives superior performance.
Non-contact tonometry using Corvis ST: analysis of corneal vibrations and their relation with intraocular pressure
Agnieszka Boszczyk, Henryk Kasprzak, and Damian Siedlecki
Doc ID: 352037 Received 15 Nov 2018; Accepted 16 Jan 2019; Posted 16 Jan 2019 View: PDF
Abstract: The aim of this study was to determine characteristic frequencies of corneal vibrations occurring during air-puff intraocular pressure measurement using Corvis ST tonometer. Relations of frequency of the corneal vibrations with intraocular pressure IOP were examined. Two selected vibration frequencies: MAF (frequency with maximum amplitude) and CM50 (mass center of the frequency distribution area, for which the amplitude was higher than 50%) present significant correlations with non-corrected IOP (CVS-IOP) and biomechanical corrected IOP (bIOP). The highest correlation was found between the mean values of CM50 and bIOP (r = 0.91). Based on the results obtained, it can be stated that vibration frequencies of corneal peaks are closely related to the real intraocular pressure and the central corneal thickness CCT.
Concept and optical design of a compactcross-grating spectrometer
Verena Bagusat, Daniel Thomae, Tobias Hönle, Matthias Kraus, Erik Foerster, Robert Brüning, and Robert Brunner
Doc ID: 345574 Received 11 Sep 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019 View: PDF
Abstract: The concept of a new compact echelle inspired cross-grating spectrometer isintroduced and a specific optical design is presented. The new concept targets to achievesimultaneously a high spectral resolution, a wide accessible spectral range and compactdimensions. The essential system novelty concerns the combination of different aspects: theimplementation of a crossed grating comprising both the main dispersion and orderseparation, a folded reflective beam path, which enables a reduction of the system volumeand, the introduction of a form-adjustable mirror for aberration compensation. The exemplaryoptical design offers a spectral bandwidth ranging from 330–1100 nm with spectral resolutionbetter than 1.4 nm in the 4th and 0.4 nm in the 11th order. The optical setup covers a volume of110 x 110 x 30 mm3.
Analysis of torsional eye movementsusing the corneal birefringence pattern
Marcelina Sobczak, Magdalena Asejczyk-Widlicka, Agnieszka Szafraniec, and Piotr Kurzynowski
Doc ID: 349099 Received 26 Oct 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019 View: PDF
Abstract: The literature mentions several invasive methods to measure the degree of thecompensatory torsional eye movement during the head-tilt. Nevertheless, none of them haveyielded universally clinical tests. This study focuses on the optical system (with circularpolarizer) for a non-invasive acquisition of the corneal birefringence pattern (isochromes).The acquired isochromes are quadrangular in shape and unique for each eye, as well asindependent of the head-rotation angle. Obtained results suggest that the isochromesorientation analysis could be an effective method to accurately measure the degree of thecompensatory torsional eye movement.
A unified approach to tear film surface analysis withhigh speed videokeratoscopy
Clara Llorens Quintana, Dorota Szczesna-Iskander, and D. Robert Iskander
Doc ID: 349234 Received 26 Oct 2018; Accepted 12 Jan 2019; Posted 15 Jan 2019 View: PDF
Abstract: Placido disk videokeratoscopy, when used in a dynamic acquisition mode, can be utilized for non-invasiveassessment of tear film quality. The different commercially available videokeratoscopes that incorporate anautomatic option to evaluate tear film do not provide consistent measurements due to differences in their designsas well as differences in the algorithms used to analyze the images. A standardized algorithm that can be applied todifferent instruments is here developed. Results show that by applying the proposed methodology in two differentvideokeratoscopes the agreement among the estimated tear film parameters considerably improves. Thisrepresents a step forward in the normalization of tear film assessment.
Hyperspectral imaging in color vision research:Tutorial
David Foster and Kinjiro Amano
Doc ID: 347289 Received 01 Oct 2018; Accepted 11 Jan 2019; Posted 15 Jan 2019 View: PDF
Abstract: This tutorial offers an introduction to terrestrial and close-range hyperspectral imaging and some of its uses inhuman color vision research. The main types of hyperspectral cameras are described together with proceduresfor image acquisition, postprocessing, and calibration for either radiance or reflectance data. Imagetransformations are defined for colorimetric representations, color rendering, and cone receptor andpostreceptor coding. Several example applications are also presented. These include calculating the colorproperties of scenes, such as gamut volume and metamerism, and analyzing the utility of color in observertasks, such as identifying surfaces under illuminant changes. The effects of noise and uncertainty areconsidered both in image acquisition and in color vision applications.
Improving the Uniformity of Holographic Recording Using MultilayerPhotopolymer: Part I. Theoretical Analysis
Ra'ed Malallah, Haoyu Li, Yue Qi, Derek Cassidy, Inbarasan Muniraj, Nebras Alattar, and John Sheridan
Doc ID: 355529 Received 17 Dec 2018; Accepted 11 Jan 2019; Posted 11 Jan 2019 View: PDF
Abstract: An experimental and theoretical investigation of the preparation and exposure of multi-layerphotosensitive materials is presented. It is shown how the recorded change in the refractiveindex in each layer depends on the dye (photosensitizer) concentrations in each layer. It isalso shown how the photosensitive materials properties in each layer can be controlled tooptimize some recording characteristics for particular applications. To do so, a set ofequations, predicting the amplitude of higher harmonics refractive index amplitudes inducedin the material layers with depth during exposure, are derived. This results in a technique forvarying the dye concentration in each layer of a multi-layer, so as optimize volumediffraction grating performance. In Part I of this paper the 3D Nonlocal PhotopolymerizationDriven Diffusion (NPDD) model is applied to calculate the resulting combined multi-layerabsorption and polymerization processes. The NPDD describes the time varying behaviorstaking place during exposure in such photopolymer materials. Simulations are performed foran Acrylamide/Polyvinyl Alcohol (AA/PVA) based photopolymer containing Erythrosine-B(EB) dye. It is predicted that in general non-uniform gratings are formed, with the resultingrefractive index being distorted both from the ideal sinusoidal cross-sectional spatialdistribution and also with depth. This agrees with previous results indicating that increasingthe thickness of a single photopolymer layer does not in practice lead to an ever increasingangular selectivity. In Part II of this paper it is confirmed experimentally that a suitablymodified multi-layer can be used to increase grating angular selectivity, i.e. reduce the widthof the off-Bragg replay curve.
Improving the Uniformity of Holographic Recording Using MultilayerPhotopolymer: Part II. Experimental Results
Ra'ed Malallah, Haoyu Li, Yue Qi, Derek Cassidy, Inbarasan Muniraj, Nebras Alattar, and John Sheridan
Doc ID: 355530 Received 17 Dec 2018; Accepted 11 Jan 2019; Posted 11 Jan 2019 View: PDF
Abstract: In the first part of this study, , a 3D Nonlocal Photopolymerization Driven Diffusion(NPDD) model was developed and applied to simulate the absorption and polymerizationtaking place during holographic exposures of a multi-layer. The Beer-Lambert law was usedto choose appropriate dye concentrations for each layer, with the objective of improving theresulting volume grating uniformity and thus diffraction characteristics. The predictionsmade, using previously estimated physical parameter values, indicated that improvements inthe uniformity of the recorded modulation were possible. In this paper the results ofexperiments carried out to explore the validity of these predictions are presented.Improvements in material response are demonstrated experimentally, with improved gratingdiffraction (narrower angular selectivity) being observed for appropriately sensitized multilayers.
Polarization singularities in a stress-engineered optic
Ashan Ariyawansa, Kevin Liang, and Thomas Brown
Doc ID: 348402 Received 22 Oct 2018; Accepted 08 Jan 2019; Posted 08 Jan 2019 View: PDF
Abstract: We develop a simplified version of a recently presented model to simulate the oblique propagation ofpolarized light through a thick birefringent element known as a stress-engineered optic (SEO). We usethis model to analyze the formation and the evolution of three polarization singularities - stars, lemons,and monstars - and experimentally verify the theoretical predictions. We also show how an SEO can beused to generate statistically rare monstar singularities.
Complete Mueller matrix from a partialpolarimetry experiment: the twelve-elementcase
Oriol Arteaga and Razvigor Ossikovski
Doc ID: 349767 Received 31 Oct 2018; Accepted 08 Jan 2019; Posted 08 Jan 2019 View: PDF
Abstract: Conventional generalized ellipsometry instrumentation is capable of measuringtwelve out of the sixteen elements of the Mueller matrix of the sample. The missing column(or row) of the experimental partial Mueller matrix can be analytically determined underadditional assumptions. We identify the conditions necessary for completing the partialMueller matrix to a full one. More specifically, such a completion is always possible if thesample is nondepolarizing; the fulfilment of additional conditions, such as the Mueller matrixexhibiting symmetries or being of special two-component structure, are necessary if thesample is depolarizing. We report both algebraic and numerical procedures for completing thepartial twelve-element Mueller matrix in all tractable cases and validate them on experimentalexamples.
Pre-location image stitching method based on flexibleand precise boresight adjustment using Risley prisms
Anhu Li, Xingsheng Liu, Wei Gong, Wansong Sun, and Jianfeng Sun
Doc ID: 349756 Received 31 Oct 2018; Accepted 08 Jan 2019; Posted 09 Jan 2019 View: PDF
Abstract: A pre-location image stitching method is proposed for the scan imaging system using Risley prisms. By confiningthe feature-based stitching procedure to several pre-located overlap areas in multiple sub-region images, theproposed method reduces the computational complexity of feature extraction and image registration. Experimentresults and analysis have validated the feasibility and robustness of the overlap pre-location algorithm, which canenhance the image stitching efficiency by 21.89% at least and by 39.38% at most. In addition, the composite imageobtained from pre-location stitching procedure can achieve a large field of view while maintaining high resolution.
High resolution augmented reality 3D display withuse of lenticular lens array holographic opticalelement
Huan Deng, Cong Chen, Min-Yang He, Jiao-Jiao Li, Han-Le Zhang, and Qiong-Hua Wang
Doc ID: 351354 Received 08 Nov 2018; Accepted 07 Jan 2019; Posted 09 Jan 2019 View: PDF
Abstract: An augmented reality (AR) three-dimensional (3D) display based on one-dimensional integralimaging (1DII) by using a lenticular lens array holographic optical element (LLA-HOE) is proposed.The 3D image of the 1DII has higher vertical resolution compared with that of the conventionalintegral imaging (II) whose resolution is sharply reduced for providing quasi-continuous viewpointsin both the horizontal and vertical directions. The proposed 3D display consists of a projector and anLLA-HOE and it is compact. As an image combiner, the LLA-HOE can diffract the Bragg matchedlight rays that has the same wavelength and incident angle as the original reference wave and it canfunction as a lenticular lens array to reconstruct 3D image but transmit the other light rays emittedfrom the surroundings. In the experiment, an 80×80mm sized LLA-HOE is recorded, and acombination of a high resolution 3D virtual image and a real 3D object is presented by the proposedAR 3D display.
Sampling approach for singular system computation ofa radiation operator
Raffaele Solimene, Maria Maisto, and Rocco Pierri
Doc ID: 347437 Received 03 Oct 2018; Accepted 07 Jan 2019; Posted 07 Jan 2019 View: PDF
Abstract: The problem of computing the singular system of the radiation operator pertaining to the case of stripcurrents is dealt with. The associate eigenvalue problem involves a space-variant operator whose kernelis not band-limited. As a consequence, the sampling approach, that has been recently introducedfor computing the eigenwavefronts of some band-limited linear space-invariant imaging systems, cannotbe used as such. To overcome this drawback, it is shown that the kernel function can be recast as avarying band-limited function. This allows to exploit the pseudo-sampling series theory from which asampling approximation of the kernel function is derived and eventually used to set the discrete eigenvalueproblem. In particular, unlike the classical sampling approach, the sampling points turn out tobe non-uniformly distributed. Some numerical examples are used to check the theory. It is shown thatthe most significant part of the singular system can be very accurately computed by using a number ofsamples slightly greater than the Shannon number.
An ultraviolet broadband plasmonic absorber withdual visible and near-infrared narrow bands
Huixuan Gao, Da-Peng Zhou, Wenli Cui, Zhi Liu, Yun Liu, Zhenguo Jing, and Wei Peng
Doc ID: 347471 Received 04 Oct 2018; Accepted 07 Jan 2019; Posted 07 Jan 2019 View: PDF
Abstract: We propose an ultraviolet broadband plasmonic absorber with dual narrow bands located separately in the visibleand near-infrared regions. It employs a three-layer dielectric and metallic film structure based on ring squarenanodisk array. The interaction of surface plasmon resonance with a Fabry-Perot (FP) cavity resonance results inperfect absorption. The absorption efficiency is greater than 99.9% at wavelengths of 660 nm and 919 nm (visibleand near-infrared), respectively, under normal incidence. In the ultraviolet region from 240 to 500 nm, theabsorption efficiency can be achieved over 90%. The geometric symmetry of ring square makes the perfectabsorber polarization-independent, and insensitive to large incident angle. This perfect absorber that combinesboth broadband and narrowband absorption can be used as sensors, solar cells or thermal emitters within oneintegrated device with further investigations.
Generalized Hanbury Brown-Twiss effect for Stokes parameters
David Kuebel and Taco Visser
Doc ID: 353041 Received 29 Nov 2018; Accepted 07 Jan 2019; Posted 15 Jan 2019 View: PDF
Abstract: The classic experiments by Hanbury Brown and Twiss (HBT) were concerned with the correlation of intensity fluctuations at two different positions in a wave field. We generalize the HBT effect that occurs in random electromagnetic beams by examining its polarization-resolved version. This leads naturally to the concept of correlations of fluctuations of the four Stokes parameters. We calculate the correlations of such ``Stokes fluctuations' for the case of Gaussian statistics. When the two points of observation coincide, these correlations reduce to ``Stokes scintillations.' Our work reveals a new layer of complexity in random beams by showing that the HBT effect and the scintillation coefficient are just two of many correlations that are present. We illustrate that, in general, the fluctuations of the various Stokes parameters are all correlated by studying beams and source with different polarization states.
Physically meaningful Monte-Carlo approach to thefour-flux solution of a dense multilayered system
Elena de la Hoz López-Collado, Rodrigo Alcaraz de la Osa, Dolores Ortiz, Jose Saiz, Fernando Moreno, and Francisco Gonzalez
Doc ID: 346707 Received 26 Sep 2018; Accepted 06 Jan 2019; Posted 07 Jan 2019 View: PDF
Abstract: Due to the complexity of the radiative transfer equation, light transport problems are commonly solvedusing either models under restrictive assumptions, e.g., N-flux models where infinite lateral extension isassumed, or numerical methods. While the latter can be applied to more general cases, it is difficult to relatetheir parameters to the physical properties of the systems under study. Hence in this contribution wepresent, firstly, a review of a four-flux formalism to study the light transport problem in a plane-parallelsystem together with a derivation of equations to evaluate the different contributions to the total absorptanceand, secondly, as a complementary tool, a Monte Carlo algorithm with a direct correspondencebetween its inputs and the properties of the system. The combination of the four-flux model and theMonte Carlo approach provides: i) all convergence warranties since the formalism has been establishedas a limit and ii) new added capabilities, i.e., both temporal (transient states) and spatial (arbitrarily inhomogeneousmedia) resolution. The support between the theoretical model and the numerical tool isreciprocal since the model is utilized to set a Monte Carlo discretization criterion, while the Monte Carloapproach is used to validate the aforementioned model. This reinforces the parallel approach used in thiswork. Furthermore, we provide some examples to show its capabilities and potential, e.g., the study ofthe temporal distribution of a delta-like pulse of light.
Small-aperture optics for the presbyope: docomparable designs of corneal inlays andintraocular lenses provide similartransmittances to the retina?
Wm. Neil Charman, Yongji Liu, and David Atchison
Doc ID: 352020 Received 15 Nov 2018; Accepted 04 Jan 2019; Posted 07 Jan 2019 View: PDF
Abstract: The near-vision performance of emmetropic presbyopes can be improved by themonocular surgical implantation of small-aperture corneal inlays or intraocular lenses whichcontain either an annular or circular stop to increase ocular depth-of-focus. Ray tracing is used toshow that, although different stop designs and positions may produce similar axial imagery andincreases in depth-of-focus, off-axis the vignetting effects associated with the distance betweenthe stop and the iris aperture result in different field dependences for the pupil transmittance.The implications of these effects, and of implanting a stop in only one eye, are discussed.
Invariance to low-level features and partial transferover space in the tilt-after-effects evoked bysymmetrical patterns
Yui Sakata, Ken Kurematsu, Nobuhiko Wagatsuma, and Ko Sakai
Doc ID: 347260 Received 01 Oct 2018; Accepted 03 Jan 2019; Posted 04 Jan 2019 View: PDF
Abstract: The symmetry axis is the midline that divides a pattern into congruent halves, which is physicallynonexistent but evokes tilt-after-effect (TAE). To investigate the cortical correspondence of thesymmetry axis, we examined the invariance of symmetry-induced TAE with regard to low-levelvisual features, and the spatial transfer of TAE over visual fields. When the adaptation pattern wasrotated and changed sequentially with the orientation of the symmetry axis unchanged, themeasured TAE decreased only slightly (18%) compared to stationary patterns. This effect persistedwhen the adaptation and test patterns were presented in different visual fields. These resultsindicate that the cortical representation of symmetry is generated independently of low-levelfeatures and involves higher-level visual areas.
Spectra restoration and image reconstruction of J0amplitude transmittance object with circular symmetry
Hsun-Ching Hsu, Junhong Weng, and Pin Han
Doc ID: 349264 Received 26 Oct 2018; Accepted 03 Jan 2019; Posted 04 Jan 2019 View: PDF
Abstract: It is known that image reconstruction (Talbot images) and spectra restoration (Talbotspectra) phenomena can be found for light diffraction of linear periodic structures. Inthis work the possibility to find similar effects for a circular symmetric object,especially for the one with amplitude transmittance J0 (ρ ) (zero order Besselfunction of the first kind) is discussed theoretically. The transfer function approachand spatial-spectral correspondence relationship are used to investigate these effects,and conditions for image reconstruction and spectra restoration in near-field areobtained. The discussion for more general form of amplitude transmittance is alsoincluded and a comparison between the two types (linear periodic and circularsymmetric structures) is made.
Diffraction from 2D orthogonal non-separable periodic structures: Talbot distance dependence on the number theoretic properties of the structures
Davud Hebri and Saifollah Rasouli
Doc ID: 352341 Received 19 Nov 2018; Accepted 02 Jan 2019; Posted 03 Jan 2019 View: PDF
Abstract: In this work, the diffraction based discrimination of two-dimensional (2D) orthogonal separable and non-separable periodic structures and prediction of the reduced Talbot distances for 2D orthogonal nonseparable periodic structures are presented. 2D orthogonal periodic structures are defined and classified into separable (multiplicative or additive) and non-separable categories with the aid of a spatial spectrum lattice. For both of the separable and non-separable cases, the spatial spectra or far-field impulses are 2D orthogonal lattices. We prove that for a 2D orthogonal separable structure, in addition to the DC impulse there are other impulses on the coordinate axes. As a result, if all the spectrum impulses of a structure on the coordinate axes, except for the DC impulse, vanish we conclude that the structure is non-separable. In the second part of this work, using a unified formulation, the near-field diffraction of the 2D orthogonal separable and non-separable periodic structures are investigated. In general, the Talbotdistance equals the least common multiple of the individual Talbot distances in the orthogonal directions, say z_t = z_lcm. For the 2D orthogonal non-separable periodic structures having Fourier coefficients only with odd indexes, we have found surprising results. It is shown that for this kind of structure, the Talbot distance strongly depends on the number theoretic properties of the structure. Depending on the ratio of the structure’s periods in the orthogonal directions, px/py , the Talbot distance reduces to z_lcm/2 , z_lcm/4 , or z_lcm/8 . In addition, for the 2D orthogonal non-separable sinusoidal grating, we show that, regardless of the value of px/py , self-images are formed at distances smaller than the conventional Talbot distances attributed to px and py that we name as the Reduced Talbot (RT) distances. Half-way between two adjacent RT distances, the formation of negative-self-images with a complementary amplitude of the self-images is predicted. Half-way between two adjacent self-image and negative-self-image, sub-images are formed. As another interesting result we show that the intensity patterns of the sub-images are 2D multiplicatively separablewith halved periods in both directions. Finally, we show that 2D almost-periodic structures with impulses on zone-plate-like concentric circles have self-images under plane wave illumination.
A reciprocal 360-degree 3D light-field image acquisition and display system
Ali YONTEM, Kun Li, and Daping Chu
Doc ID: 347226 Received 01 Oct 2018; Accepted 25 Dec 2018; Posted 03 Jan 2019 View: PDF
Abstract: A reciprocal 360-degree three-dimensional light-field image acquisition and display system was designed using a common catadioptric optical configuration and a lens array. Proof-of-concept experimental setups were constructed with a full capturing part and a truncated display section to demonstrate that the proposed design works without loss of generality. Unlike conventional setups, which record and display rectangular volumes, the proposed configuration records 3D images from its surrounding spherical volume in the capture mode and project 3D images to the same spherical volume in the display mode. This is particularly advantageous in comparison to other 360-degree multi-camera and multiple projector display systems which require extensive image and physical calibration. The issue due to the pixel size difference between the available imaging sensor and the display was also addressed. A diffractive microlens array matching the sensor size is used in the acquisition part whereas a vacuum cast lens array matchingthe display size is used in the display part with scaled optics. The experimental results demonstrate the proposed system design works well and in good agreement with the Zemax simulation results.
Comparison of refractive error measurements by three different models of autorefractors and subjective refraction in young adults
Justyna Wosik, Małgorzata Patrzykont, and Jacek Pniewski
Doc ID: 349755 Received 31 Oct 2018; Accepted 21 Dec 2018; Posted 21 Dec 2018 View: PDF
Abstract: In the paper the accuracy of noncycloplegic refractive error measurements performed by three autorefractors: Nidek ARK 510A, Visionix L80 Wave+, and Shin-Nippon NVision-K5001, compared with subjective refraction in young adults, is analyzed using statistical methods. The analysis is carried out in terms of spherical equivalent, astigmatism and two Jackson crossed-cylinder vectors. A group of 51 subjects aged 19– was examined. The differences between objective refraction measured by autorefractors are not statistically significant in both spherical equivalent and cylindrical components. However, in comparison with subjective refraction the best agreement in spherical equivalent was provided by K 5001. For all instruments differences in spherical equivalent between objective and subjective refraction are statistically significant.
The development of polarization speckle based onrandom polarization phasor sum
Chunmei Zhang, Sean Horder, Tim Lee, and Wei Wang
Doc ID: 345780 Received 24 Sep 2018; Accepted 20 Dec 2018; Posted 21 Dec 2018 View: PDF
Abstract: The random walk approach has been extended and applied to study the development of polarization speckle by takingthe vector nature into account for stochastic electric fields. Based on the random polarization phasor sum, the first andsecond moments of the Stokes parameters of the resultant polarization speckle have been examined. Under certainassumptions about the statistics of the component polarization phasors that make up the sum, we present some of thedetails of the spatial derivation that leads to the expressions for the degree of polarization and the newly proposed Stokescontrast which are suitable for describing the polarization speckle development. This vectorial extension of the randomwalk will provide an intuitive explanation for the development of the polarization speckle.
Improving tangential resolution in photoacoustic tomography using sensors with Gaussian apodization
Ratan Saha, Pankaj Warbal, and Manojit Pramanik
Doc ID: 348464 Received 16 Oct 2018; Accepted 20 Dec 2018; Posted 21 Dec 2018 View: PDF
Abstract: Photoacoustic tomographic (PAT) image reconstruction with apodized sensors is discussed. A Gaussian function was used to model axisymmetric apodization of sensors and its full width at half maximum (FWHM) was varied to investigate the role of apodization on the PAT image reconstruction. The well known conventional delay-and-sum (CDAS) and recently developed modified delay-and-sum (MDAS) algorithms were implemented to generate reconstructed images. The performance of these algorithms were examined by comparing simulated images formed by these methods and that of ideal point detectors. Simulations in two dimensions were conducted using k-Wave tool box for three different phantoms. The results produced by the CDAS method are very close to that of ideal point detectors when FWHM of the Gaussian function is small. The MDAS algorithm for flat sensors provides excellent results (comparable to that of point detectors) when FWHM of the Gaussian profile is large. This study elucidates how sensor apodization affects the PAT image reconstruction.