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A Generalized Equation for Real-World ImageEnhancement by Milano Retinex Family

Michela Lecca

DOI: 10.1364/JOSAA.384197 Received 22 Nov 2019; Accepted 02 Apr 2020; Posted 02 Apr 2020  View: PDF

Abstract: Milano Retinexes are spatial color algorithms grounded on the Retinex theory and widely applied to enhance the visual content of real-world color images. In this framework, they process the color channelsof the input image independently and re-scale channel by channel the intensity of each pixel p by theso-called local reference white, i.e. a strictly positive value, computed by re-working a set of features sampled around p. The neighborhood of p to be sampled, its sampling, the features to be processed, as well asthe mathematical model for the computation of the local reference white vary from algorithm to algorithm,determining different levels of enhancement. Based on the analysis of a group of Milano Retinexes, thiswork proves that the Milano Retinex local reference whites can be expressed by a generalized equation,whose parameters model specific aspects of the Milano Retinex spatial color processing. In particular,tuning these parameters leads to different Milano Retinex implementations. This study contributes tobetter understand the similarity and the differences among the members of the Milano Retinex familyand provides new taxonomic schemes of them based on their own mathematical properties.

Gaussian spatial-polarization entanglement in afolded Mach-Zehnder interferometer

Soumya Asokan and Jebathilagar Ivan

DOI: 10.1364/JOSAA.386502 Received 02 Jan 2020; Accepted 01 Apr 2020; Posted 02 Apr 2020  View: PDF

Abstract: Gaussian spatial-polarization entanglement in a coherent vectorial paraxial lightfield is studied. Detection of spatial-polarization entanglement through fringe movement onrotation of a linear polarizer, with the light field passing through the polarizer, is outlined. Thefringe movement is shown to be a sufficient condition for the detection of spatial-polarizationentanglement in coherent paraxial vector light fields. Two Gaussian light fields with a smallrelative tilt but with significant spatial overlap, and with orthogonal polarizations is shown topossess close to 1 ebit of spatial-polarization entanglement. Tunable Gaussian spatial-polarizationentanglement is experimentally demonstrated in a folded Mach-Zehnder interferometer.

Effect of hair removal on solar UV transmission into skin andimplications for melanoma skin cancer development

Xiyong Huang, Mike Protheroe, Ahmed Al-Jumaily, Sharad Paul, and Andrew Chalmers

DOI: 10.1364/JOSAA.387558 Received 07 Jan 2020; Accepted 01 Apr 2020; Posted 02 Apr 2020  View: PDF

Abstract: Melanoma is the severest type of skin cancer. As distinct from many other cancer types, theincidence of melanoma has been increasing steadily over the last century. Discovering newrisk factors of melanoma will not only raise public awareness but also potentially contributeto the improvement of skin cancer protection in the future. Nowadays, the tendency ofshaving skin hair is becoming increasingly popular for aesthetic purposes. However, humanhair serves several functions, one of which is ultraviolet (UV) protection for the skin. What ismore, stem cells found in the follicles of hair could be the origin of melanoma uponexposure to ultraviolet radiation (UVR). Therefore, it is of interest to investigate the effect ofshaving on solar UV transmission in the skin. To achieve that, two groups of skin models areconstructed in TracePro software; one with unaltered hair and one with shaved hair. The UVtransport in the models is simulated using the Monte Carlo method and the absorptions inthe stem cells layer are compared. It is found that, shaving will increase the UV transmissionto the follicular stem cells to a certain degree. More specifically, shaving limbs will generallyincrease the solar UV transmission from about 5% to 20% in the UV wavelength range.

Application of Gaussian pulsed beam decompositionin modeling optical systems with diffraction grating

Norman Girma Worku and Herbert Gross

DOI: 10.1364/JOSAA.390089 Received 07 Feb 2020; Accepted 30 Mar 2020; Posted 31 Mar 2020  View: PDF

Abstract: A diffraction grating is one of the most commonly used component in ultrafast optical systems suchas pulse stretchers and compressors. Hence, modeling the temporal dispersion and the spatio-temporaldistortions associated with the angular dispersion of a diffraction grating is very crucial for wave optical modeling of such systems. In this paper, the Gaussian pulsed beam decomposition (GPBD) methodis extended to handle the propagation of ultrashort pulses, with arbitrary spatial and spectral profiles,through complex ultrashort pulse shaping systems containing diffraction grating. Although the diffraction efficiencies are not rigorously computed, the GPBD method enables modeling of the large angulardispersion of idealized diffraction gratings without running into impractically large number of spectralsamples as in the case of the Fourier transform based methods. The application of the extended method isdemonstrated by performing the wave optical propagation of an ultrashort pulse through a single diffraction grating and then through a Treacy compressor system. By combining the Treacy compressor with theMartinez grating pair stretcher with internal lenses, the pulse shaping through complete chirped pulseamplification (CPA) setup is modeled. Finally, the effects of using real dispersive lenses in the Martinezstretcher on the output pulse of the CPA setup are presented. For analysis of the output pulses, methodsof computing the spatio-temporal and the spatio-spectral amplitudes of the output pulse from the phasecorrect superposition of individual Gaussian pulsed beams are presented.

Vector wave simulation of active imaging throughrandom media

Zhean Shen and Aristide Dogariu

DOI: 10.1364/JOSAA.382152 Received 31 Oct 2019; Accepted 30 Mar 2020; Posted 31 Mar 2020  View: PDF

Abstract: When a target is embedded in random media, the quality of optical imaging can be improved by actively controllingthe illumination and by exploiting vector wave properties. A rigorous description, however, requires expensivecomputational resources to fully account for the electromagnetic boundary conditions. Here we introduce astatistically-equivalent, scaling model that allows reducing significantly the complexity of the problem. The newscheme describes the entanglement between the local wave vector and the polarization state in random media, andalso accounts for cumulative properties such as geometric phase. The approach is validated for different scenarioswhere the coherent background noise alters substantially the performance of active imaging.

When does ‘bright’ mean ‘prototypical’?Color-term modifiers in eight Europeanlanguages, examined with color-survey data

Mari Uusküla and David Bimler

DOI: 10.1364/JOSAA.382399 Received 06 Nov 2019; Accepted 30 Mar 2020; Posted 31 Mar 2020  View: PDF

Abstract: Certain modified color terms encountered in a multi-language corpus of unconstrained colornaming data, elicited with 65 Color-aid Corporation tiles, can be glossed into English as‘bright (or vivid) X’ (e.g. Estonian ‘ere-X’) while other modifiers are glossed ‘light’ or‘dark’. However, translation between languages or into the terms of colorimetry is neverassured. We address the problem empirically by examining the denotata of each modifiedterm and treating its uses as a distribution across a metric color space in which tiles arelocated as points. We compared each distribution with that of the unmodified term X,identifying the latter with the focus of X (the within-language consensus about the mostprototypical exemplar of X). In some cases the modifiers operate as ‘bright’ in the sense of‘intense’ or ‘saturated’, so ‘bright-X’ and ‘X’ share a centroid, but this is not universal.

Feature Matching based on Curve Descriptor and LocalD-Nets for Fish-eye Images

Yakun Zhang, Hongsheng Zhang, and Wenming Zhang

DOI: 10.1364/JOSAA.385921 Received 13 Dec 2019; Accepted 30 Mar 2020; Posted 31 Mar 2020  View: PDF

Abstract: Most feature matching algorithms based on perspective images, such as SIFT, SURF, or DAISY, constructtheir feature descriptors from the neighborhood information of feature points. Large nonlinear distortion resultsin different amount of neighborhood information at different feature points within the fish-eye images, especiallyfor the case that a feature pixel is at the central region, and the corresponding feature pixel is at the periphery.Differently, D-nets is a feature matching algorithm based on global information. It is more robust, but it is timeconsuming. In this paper, we employ SIFT detector to extract feature pixels, and then we propose a novel featurematching strategy based on D-Nets algorithm. we modify the linear descriptors in the traditional D-Nets algorithmand propose a curve descriptor based on the hemisphere model of fish-eye image. In the traditional D-Netsalgorithm, each feature point is described by all other pixels of the entire image, and complicated calculationscause slow matching speed. To solve this problem, we convert the traditional global D-Nets into a novel local DNets. In the experiment, we obtain image pairs from the real scenery using the binocular fish-eye camera platform.Experimental results show that the proposed local D-Nets method can achieve more than three times the initialmatching pixels, the PBM is reduced by 40% compared with the best performing method among the comparisonmethods. In addition, the matching pixel pairs obtained by the proposed method are evenly distributed, either inthe center region with small distortion or in the peripheral region with large distortion. Meanwhile, the local DNets algorithm is sixteen times less than that of the global D-nets algorithm.

Influence of naturalness of chroma and lightnesscontrast modulation on colorfulness adaptation innatural images

Taishi Masumitsu and Yoko Mizokami

DOI: 10.1364/JOSAA.382414 Received 08 Nov 2019; Accepted 26 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: We investigated as to whether the naturalness of images modulated by a combination of chroma and lightnesscontrast affects the colorfulness perception. Four types of modulated images with different combinations ofchroma and lightness contrast were used as adaptation stimuli. After adapting to one of the adaptation stimuligroups, observers judged the colorfulness of test images that were also modulated by the different combinations ofchroma and lightness contrast. Our results showed that the combination of chroma and lightness contrastmodulation affected the strength of colorfulness adaptation. The results also indicated that when adapting toimages that exhibited high naturalness, the effect of colorfulness adaptation was strong. It was suggested that thenaturalness of chroma and lightness combination is an important factor for colorfulness adaptation.

Propagation of fully and partially coherent Flat-toppedmulti Gaussian beams through axicons

Fatima Thabit, Abdu Alkelly, and Mohammed Shukri

DOI: 10.1364/JOSAA.386820 Received 14 Jan 2020; Accepted 23 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Theoretically, we have investigated the propagation of fully and partially coherent Flat-topped multi-GaussianBeams (FMGB) through classical and logarithmic axicons. The method of stationary phase applied to the Fresneldiffraction integral for intensity distribution has led to an applicable relations. The influence of axicon base angle,beam width, beam flatness and coherence length with intensity distribution were studied. A number of results havebeen analyzed and discussed revealing some important conclusions. During this investigation a specific interest hasbeen given toward producing uniform intensity and long focal depth.

Scintillation Averaging and Fade Statistics

Scot Shaw

DOI: 10.1364/JOSAA.388567 Received 20 Jan 2020; Accepted 23 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: This work develops expressions for the variance and power spectral density (PSD) of atmosphericallyinduced amplitude fluctuations of a propagating beam of light, also known as scintillation. This extendsa recently published analytic approach for atmospheric propagation studies, previously applied to thephase properties of a propagating beam. In addition to laying out the general principles for manipulating log-amplitude expressions, this work develops novel expressions for scintillation under aperture,path, wavelength, and temporal averaging, first separately and then as a unified expression. The PSDexpression is then used to find several statistics of fades of given depth and duration, including fadeprobability, rate, and average duration. Results are shown throughout to agree with existing literatureand wave-optics simulations.

Optical-vortex diagnostics via Fraunhofer slitdiffraction with controllable wavefront curvature

Aleksandr Bekshaev, Lidiya Mikhaylovskaya, Satyajeet Patil, Vijay Kumar, and Ravindra Singh

DOI: 10.1364/JOSAA.388926 Received 23 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: Far-field slit-diffraction of circular optical-vortex (OV) beams is efficient for measurement of the topological charge (TC)magnitude but does not reveal its sign. We show that this is because in the common diffraction schemes the diffractionplane coincides with the incident OV waist plane. Based on the examples of Laguerre-Gaussian incident beamscontaining a spherical wavefront component, we demonstrate that the far-field diffracted beam profile possesses anasymmetry depending on the incident wavefront curvature and the TC sign. This finding enables simple and efficientways for the simultaneous diagnostics of the TC magnitude and sign, which can be useful in many OV applications,including the OV-assisted metrology and information processing.

Testing scalar diffraction theory: Gaussian beamon a slit

Luka Zurak, Velimir Labinac, Natasa Erceg, Ivica Aviani, Marko Jusup, and Marin Karuza

DOI: 10.1364/JOSAA.388703 Received 21 Jan 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: We recorded diffraction patterns using commercially available slit and sensor over a wide range of experimental circumstances, including near- and far-field regimes and oblique incidence at large angles. Wethen compared the measured patterns with theoretical intensity curves calculated via the numerical integration of formulas derived within the framework of scalar diffraction theory. Experiment and theoryshow particularly good agreement when the first Rayleigh-Sommerfeld (R-S) formula is used. The Kirchhoff formula, though problematic in the context of mathematical consistency, agrees with the first R-Sformula even for large incidence angles, whereas the second R-S formula differs visibly. To obtain sucha good agreement, we replaced the assumption of an incident plane wave with that of a Gaussian beam,and implemented geometric corrections to account for slit imperfections. These results reveal how thescope of scalar diffraction theory can be extended with a small set of auxiliary assumptions.

Optimal Laguerre-Gaussian Modes for High-IntensityOptical Vortices

Andrew Longman and Robert Fedosejevs

DOI: 10.1364/JOSAA.389031 Received 07 Feb 2020; Accepted 23 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: With increasing interest in using orbital angular momentum (OAM) modes in high-power laser systems,accurate mathematical descriptions of the high-intensity modes at focus are required for realistic modelling. In this work, we derive various high intensity orbital angular momentum focal spot intensitydistributions generated by Gaussian, super-Gaussian, and ideal flat-top beams common to high-powerlaser systems. These intensity distributions are then approximated using fitted Laguerre-Gaussian basisfunctions as a practical way for describing high-power OAM beams in theoretical and numerical models.

Band-rejection filter with high-extinction ratio usingprism-waveguide cascaded coupling system

Maowu Ran, Wenjuan Cai, Zhang Yingcong, XianPing Wang, Yanchao She, Cheng Yin, and Jian Wu

DOI: 10.1364/JOSAA.384704 Received 02 Dec 2019; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: A band-rejection filter is proposed based on a prism-waveguide cascaded coupling system, which is composed of anequilateral trapezium prism and a deposited multilayer structure. By properly adjusting the thickness of thecoupling layer and the light extinction coefficient of the guiding layer, the radiative and intrinsic dampingsmatching condition could be well satisfied, and then a series of reflectivity dips will appear in the reflectivitywavelength spectrum. Since the module of reflectivity is small than 1, thus the extinction ratio of the rejectedfrequency via the cascaded coupling system is twice as high as that of the single coupling technology. By narrowingthe guiding layer to a micrometer scale, the free spectral range is broad enough to cover the Raman spectrumscattered from the frequently-used sample. In addition, the numerically calculated results show that the light in thefree spectral range is mostly reflected with an insertion loss down to 0.45 dB. Compared to previously reportedband-rejection filters, it is relatively simple to manufacture our device, which possesses potential applications tohelp distinguish the Raman signal from the elastic scattering background.

Multispectral image fusion based pedestriandetection using a multilayer fused deconvolutionalsingle-shot detector

Yunfan Chen and hyunchul shin

DOI: 10.1364/JOSAA.386410 Received 20 Dec 2019; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Recent research has demonstrated that effective fusion of multispectral images (visible and thermal images)enables robust pedestrian detection under various illumination conditions (e.g., daytime and nighttime). However,there are some open problems such as poor performance in small-sized pedestrian detection and highcomputational cost of multispectral information fusion. This paper proposes a multilayer fused deconvolutionalsingle-shot detector (MFDSSD) that contains a two-stream convolutional module (TCM) and a multilayer fuseddeconvolutional module (MFDM). The TCM is used to extract convolutional features from multispectral inputimages. Then, novel fusion blocks are incorporated into the MFDM to combine high-level features with richsemantic information and low-level features with detailed information, aiming at generating features with strongrepresentational power for small pedestrian instances. In addition, we fuse multispectral information at multipledeconvolutional layers in the MFDM via fusion blocks. This multilayer fusion strategy adaptively makes the mostuse of visible and thermal information. In addition, using fusion blocks for multilayer fusion can reduce the extracomputational cost and redundant parameters. Empirical experiments show that the proposed approach achieves81.82% average precision (AP) on a new small-sized multispectral pedestrian dataset. The proposed methodachieves the best performance on two well-known public multispectral datasets. For example, on the KAISTmultispectral pedestrian benchmark, our method achieves 97.36% AP and 20 fps detection speed, whichoutperforms the state-of-the-art published method by 6.82% in AP and is three times faster in detection speed.

Multi-mode communication through the turbulentatmosphere

Liliana Borcea, Josselin Garnier, and Knut Solna

DOI: 10.1364/JOSAA.384007 Received 22 Nov 2019; Accepted 18 Mar 2020; Posted 19 Mar 2020  View: PDF

Abstract: A central question in free-space optical communications is how to improve the transfer of informationbetween a transmitter and receiver. The capacity of the communication channel can be increased by multiplexing of independent modes using either: (1) the MIMO (Multiple-Input-Multiple-Output) approach,where the communication is done with modes obtained from the singular value decomposition of thetransfer matrix from the transmitter array to the receiver array, or (2) the OAM (Orbital Angular Momentum) approach, which uses vortex beams that carry angular momenta. In both cases, the number of usablemodes is limited by the finite aperture of the transmitter and receiver, and the effect of the turbulent atmosphere. The goal of this paper is twofold: First, we show that the MIMO and OAM multiplexingschemes are closely related. Specifically, in the case of circular apertures, the leading singular vectors ofthe transfer matrix which are useful for communication are essentially the same as the commonly usedLaguerre-Gauss vortex beams, provided these have a special radius that depends on the wavelength, thedistance from the transmitter to the receiver and the ratio of the radii of their apertures. Second, we characterize the effect of atmospheric turbulence on the communication modes using the phase screen methodput in the mathematical framework of beam propagation in random media.

Comparison of four techniques for turbulentphase screens simulation

Mikhail Charnotskii

DOI: 10.1364/JOSAA.385754 Received 12 Dec 2019; Accepted 18 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: In the study, we introduce a new technique, Sparse spectrum with Uniform wavevectors (SU), for generation of phase screen samples. In a manner similar to the known SparseSpectrum (SS) technique, it uses trigonometric series with random discrete spectral support.However, in contrast to the SS technique, random wave vectors are uniformly distributed onindividual segments of the wave vector plane partition in the SU technique. We compare theaccuracy and computational effectiveness of the SU technique with the subharmonicscomplemented DFT technique, SS technique, and randomized DFT technique [J. Opt. Soc.Am. B 36, 3249 (2019)]. The SU and SS techniques generate unbiased samples and indicatesuperior computational effectiveness for 1 MP and larger screens.

Blues do not bring the blues: challenging conventional notions of color-emotion associations

Karen Schloss, Christoph Witzel, and Leslie Lai

DOI: 10.1364/JOSAA.383588 Received 18 Nov 2019; Accepted 15 Mar 2020; Posted 16 Mar 2020  View: PDF

Abstract: In popular culture and some scientific literature it is commonly held that yellow is happy and blue is sad, but the reason remains a mystery. There is confusion in the field about what "yellow" and "blue" refer to and this confusion prevents us from understanding the origins of color-emotion associations. In this study we disentangled the contribution of lightness, chroma, and hue in color-happiness associations. In Experiment 1 we assessed color-emotion associations for colors that were equated in lightness and chroma in CIEL*c*h* color space. In Experiment 2, we repeated Experiment 1, but also included colors that were perceptually matched for saturation. The results indicated that light high chroma colors were happy and dark low chroma colors were sad. Bluer colors were no sadder than yellower colors, and if anything bluer colors were happier than yellow colors when they were dark. These results can help guide efforts to understand the nature of color-emotion associations.

Visual losses in early-onset and late-onset Parkinson’s disease

Claudia Feitosa-Santana, Marcelo Costa, Henrique Ferraz, Luiz Augusto Andrade, Edson Amaro-Jr, Russell Hamer, Dora Ventura, and Ana Laura Moura

DOI: 10.1364/JOSAA.382042 Received 06 Nov 2019; Accepted 14 Mar 2020; Posted 16 Mar 2020  View: PDF

Abstract: Patients with Parkinson’s disease (PD) manifest losses in visual contrast sensitivity (CS). However, it is not known whether the losses are equivalent in both early-onset (EOPD) and late-onset (LOPD) patients. We evaluated spatiotemporal CS in EOPD and LOPD patients and in age-matched controls. Losses occurred in both patient groups, with more pronounced losses occurring in EOPD, consistent with the notion that non-motor symptoms are affected by age of symptom-onset. More studies of visual function in EOPD and LOPD patients are needed to better characterize the etiology of PD, perhaps permitting earlier diagnosis and/or improved treatment and management of the disease.

Designing laser beams carrying OAM for a highperformance underwater communication system

Svetlana Avramov-Zamurovic, Abbie Watnik, james lindle, and Kyle Judd

DOI: 10.1364/JOSAA.388370 Received 16 Jan 2020; Accepted 12 Mar 2020; Posted 16 Mar 2020  View: PDF

Abstract: We present a design methodology for creating a distinct laser beam set suitable for detection by usingonly the recorded intensity pattern. We consider four coherent Laguerre Gaussian (LG) beams carrying OrbitalAngular Momentum (OAM) to form the basis for optical communication. The complex electric fields of the beamsare superimposed to create 16 dissimilar intensity patterns. The presented beam set design method considers thebeam generation hardware limitations and aims to minimize the correlation among the messages and maximize theirintensity differences. After propagating the 16 messages through a water channel, we measured high correlation,intensity similarity, and R-squared values for the identical messages and low values for the different ones. Distinctclustering between the measurements for the matching messages and the rest, allows us to set a threshold in the gapamong the groupings and successfully classify the received images.

Propagation properties of partially coherent anomalous hollowbeams in quadratic-index media

Jin Gui, Lirong Bian, and Bin Tang

DOI: 10.1364/JOSAA.388566 Received 20 Jan 2020; Accepted 10 Mar 2020; Posted 11 Mar 2020  View: PDF

Abstract: Based on the generalized diffraction integral formula, analytical propagation expressions for a partially coherentanomalous hollow beam (AHB) propagating through a quadratic-index medium are derived. The distributions of intensityand Poynting vector for a partially coherent AHB through the quadratic-index medium are numerically and theoreticallystudied. It is found that the intensity and Poynting vector of the partially coherent AHB take on a periodical change. Theevolution properties of the partially coherent AHB in a quadratic-index medium are closely relevant to its transversecoherence width and the quadratic-index parameter of media.

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