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Accepted papers to appear in an upcoming issue

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Sparse coding generates curvature selectivity in V4 neurons

Yasuhiro Hatori, Tatsuroh Mashita, and Ko Sakai

Doc ID: 252524 Received 22 Oct 2015; Accepted 05 Feb 2016; Posted 05 Feb 2016  View: PDF

Abstract: The cortical area V4 produces a representation of curvature as the intermediate-level representation of an object’s shape. We investigated whether sparse coding is the principle driving the generation of the spatial properties of the receptive-field in V4 that exhibit curvature selectivity. To investigate the role of sparseness in the construction of curvature representations, we applied component analysis with a sparseness constraint to the activity of model V2 neurons that were responding to shapes derived from natural images. Our simulation results showed that single basis functions with medium degrees of sparseness (0.7–0.8) produced curvature selectivity, and their population activity produced acute curvature bias. The results support the hypothesis that sparseness plays an essential role in the construction of curvature selectivity in V4.

Spectrum of an electromagnetic light wave on scattering from an anisotropic semisoft-boundary medium

Tao Wang, Zhenfei Jiang, Xiaoling Ji, and Daomu Zhao

Doc ID: 253168 Received 09 Nov 2015; Accepted 05 Feb 2016; Posted 05 Feb 2016  View: PDF

Abstract: Spectral shifts and spectral switches of a polychromatic electromagnetic light wave on scattering from an anisotropic semisoft-boundary medium are discussed. It is shown that both the property of the incident field and the character of the scattering medium play roles in the change of spectrum of far-zone scattered field. It is also shown that the distribution of far-zone scattered spectrum, including the magnitude of the spectral shift and the direction at which the spectral switch occurs is rotational non-symmetry.

Color constancy of color deficient observers under illuminations defined by individual color discrimination ellipsoid.

Keizo Shinomori, Ruiqing Ma, and Ken-ichiro Kawamoto

Doc ID: 252086 Received 15 Oct 2015; Accepted 04 Feb 2016; Posted 04 Feb 2016  View: PDF

Abstract: We explored color constancy mechanisms of color deficient observers under red, green, blue and yellow illuminations. The red and green illuminations were defined individually by the longer axis of color discrimination ellipsoid measured by the Cambridge Color Test. Four dichromats (3 protanopes and 1 deuteranope), two anomalous trichromats (2 deuteranomalous observers) and five color normal observers were asked to complete the color constancy task by making a simultaneous surface (paper) match under asymmetrical illuminations in haploscopic view on a monitor. The von Kries adaptation model was applied to estimate cone responses. The model fits showed that for all color deficient observers under all illuminations, the adjustment of S-cone response or blue-yellow chromatically opponent responses modeled with the simple assumption of cone deletion in a certain type (S-M, S-L or S-(L+M)) was consistent with the principle of von Kries model. The degree of adaptations was similar with that for color normal observers. The results indicate that the color constancy of color deficient observers is mediated by the simplified blue-yellow color system with von Kries type adaptation effect, even in the case of brightness match, as well as by possible cone-level adaptation to S-cone when illumination produces strong S-cone stimulation, such as blue illumination.

Shaping the Arago-Poisson spot with incomplete spiral phase modulation

Lixiang Chen, Yuanying Zhang, Wuhong Zhang, and Ming Su

Doc ID: 252747 Received 29 Oct 2015; Accepted 03 Feb 2016; Posted 04 Feb 2016  View: PDF

Abstract: The Arago-Poisson spot played an important role in the discovery of the wave nature of light. We demonstrate a novel way to shape the Arago-Poisson spot by partially twisting the phase fronts of the incident light beam. We use a spatial light modulator to generate the holographic gratings both for mimicking the circular opaque objects and for modulating the spiral phase profiles. For incomplete spiral phase of five-fold and ten-fold symmetry, we observe the gradual formation of the on-axis bright spots upon propagation. Our results show that two fundamental but seemingly independent optical phenomena, namely, the Arago-Poisson spot and the OAM of light can be well connected by changing the phase height $\vartheta$ gradualy from 0 to $2\pi$. The experimental results are well interpreted visually by plotting the Poynting vector flows. Besides, based on the decomposed orbital angular momentum (OAM) spectrum, the observations can also be understood well from the controllable mixture of a fundamental Gaussian beam and an OAM beam. Our work is an elegant demonstration that spiral phase modulation can add to the optical tool to shape effectively the diffraction of light, and may have potential applications in the field of optical manipulations.

Strong suppression of forward or backward Mie scattering by using spatial coherence

Taco Visser, Hugo Schouten, and yangyundou wang

Doc ID: 257365 Received 13 Jan 2016; Accepted 03 Feb 2016; Posted 04 Feb 2016  View: PDF

Abstract: We derive analytic expressions relating Mie scattering with partially coherent fields to scattering with fully coherent fields. These equations are then used to demonstrate how the intensity of the forward- or the backward-scattered field can be suppressed several orders of magnitude by tuning the spatial coherenceproperties of the incident field. This method allows the creation of cone-like scattered fields, with the angle of maximum intensity given by a simple formula.

Refraction in electrically-thin inhomogeneous media

Omar Ramahi and Miguel Ruphuy

Doc ID: 252546 Received 23 Oct 2015; Accepted 03 Feb 2016; Posted 05 Feb 2016  View: PDF

Abstract: This work presents a new formulation for refraction from at electrically-thin lenses and reflectors comprised of inhomogeneous material. Inhomogeneous electrically-thin at lenses and reflectors cannot make use of Snell law since this classical formulation works solely at interfaces of planar homogeneous media. The refraction of a perpendicularly incident plane wave at a planar interface is physically explained through the phase advance of the rays within the medium. Huygen principle is then used to construct the refracted wave-front. The formulation is validated using numerical full wave simulation for several examples where the refractive angle is predicted with good accuracy. Furthermore, the formulation gives a physical insight of the phenomenon of refraction from electrically-thin inhomogeneous media.

A Simple Principled Approach for Modeling andUnderstanding Uniform Color Metrics

Michael Webster, Lorne Whitehead, and Kevin Smet

Doc ID: 251232 Received 05 Oct 2015; Accepted 01 Feb 2016; Posted 02 Feb 2016  View: PDF

Abstract: An important goal in characterizing human color vision is to order color percepts in a way that captures theirsimilarities and differences. This has resulted in the continuing evolution of “uniform color spaces,” in which thedistances within the space represent the perceptual differences between the stimuli. While these metrics are nowvery successful in predicting how color percepts are scaled, they do so in largely empirical, ad hoc ways, withlimited reference to actual mechanisms of color vision. In this article our aim is to instead begin with general andplausible assumptions about color coding, and then develop a model of color appearance that explicitlyincorporates them. We show that many of the features of empirically-defined color order systems (such as those ofMunsell, Pantone, NCS, and others) as well as many of the basic phenomena of color perception, emerge naturallyfrom simple and plausible assumptions about how color information is encoded in the visual system and how it isoptimized for the spectral characteristics of the environment.

Modified anisotropic turbulence refractive-indexfluctuations spectral model and its application inmoderate-to-strong anisotropic turbulence

Linyan Cui, Bindang Xue, and Fugen Zhou

Doc ID: 254918 Received 01 Dec 2015; Accepted 30 Jan 2016; Posted 02 Feb 2016  View: PDF

Abstract: In this study, the modified anisotropic turbulence refractive-index fluctuations spectral model is derived based onthe extended Rytov approximation theory for the theoretical investigations of optical plane and spherical wavespropagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. The anisotropic factor whichparameterizes the asymmetry of turbulence cells or eddies in the horizontal and vertical directions is introduced.General spectral power law in the range of 3-4 is also considered compared with the conventional classic value of11/3 for the Kolmogorov turbulence. Based on the modified anisotropic turbulence refractive-index fluctuationsspectrum, the analytic expressions of the irradiance scintillation index are also derived for optical plane andspherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. They areapplicable in a wide range of turbulence strength and can reduce correctly to the previously published results inthe special cases of weak anisotropic turbulence and moderate-to-strong isotropic turbulence. Calculations areperformed to analyze the derived models.

Frontally Placed Eyes vs Laterally Placed Eyes: Computational Comparison of Their Functions for Ego-motion Estimation

zhi gao, Pengfei Wang, and Ruifang Zhai

Doc ID: 248404 Received 26 Aug 2015; Accepted 29 Jan 2016; Posted 02 Feb 2016  View: PDF

Abstract: Both frontally placed eyes and laterally placed eyes are popular in nature, which one is better, this couldbe one of the most intuitive question to ask, but hardest to answer. Their most obvious difference isthat, at least as supposed in the computer vision community, stereopsis plays the central role in the visualsystem composed of frontally placed eyes (or cameras), however it is not available in the lateral configurationdue to the lack of overlapping between the visual fields. As a result, researchers have adoptedcompletely different approaches to model such two configurations and developed computational mimicsof them to address various vision problems. Recently, the advent of novel quasi-parallax conception unifiesthe ego-motion estimation procedure of these two eye configurations into the same framework andmakes systematic comparison feasible. In this paper, we intend to establish the computational superiorityof eye topography from the perspective of ego-motion estimation. Specifically, quasi-parallax is appliedto fuse motion cues from individual cameras at early stage, pixel level, and recover the translation androtation separately with high accuracy and efficiency without the need of feature matching. Furthermore,its applicability on the extended sideway arrangements are studied successfully to make our comparisonmore general and insightful. Extensive experiments on both synthetic and real data have been done, andthe computational superiority of lateral configuration is verified convincingly.

Light scattering of a Laguerre-Gaussian vortex beam by a chiral sphere

Tan Qu, Zhen-Sen Wu, Qingchao Shang, and Zheng-Jun Li

Doc ID: 255514 Received 11 Dec 2015; Accepted 28 Jan 2016; Posted 29 Jan 2016  View: PDF

Abstract: The analytical solution to the scattering of a chiral sphere by a Laguerre-Guassian vortex beam (LG) is investigated. Based on the transformation between Laguerre and Hermite Gaussian modes, and using the expansion of Hermite Gaussian beam by complex source point method, we derive a general expansion of LG vortex beam in terms of Spherical Vector Wave Functions (SVWFs). Combing with the continuous boundary conditions of electromagnetic field components, the scattering coefficients and internal field coefficients are solved. The internal field and the angular distribution of scattered field by chiral sphere located in the LG vortex beam with different topological charge are numerically simulated. The influences of beam mode, topological charge, chiral parameter and sphere radius on the scattered field are analyzed in detail. The results shown that the scattering intensity does not always increase with the increase of beam width as Gaussian beam does.

Non-coaxial Bessel-Gauss Beams

Chaohong Huang, Yishu Zheng, and Hanqing Li

Doc ID: 251947 Received 20 Oct 2015; Accepted 28 Jan 2016; Posted 02 Feb 2016  View: PDF

Abstract: We proposed a new family of non-coaxial Gauss-truncated Bessel beams through multiplying conventional symmetric Bessel beams by a non-coaxial Gauss function. These beams can also be regard as the exponential-truncated version of Bessel-Gauss beams since they can be transformed into the product of Bessel-Gauss beams and a exponential window function along a certain Cartesian axis. The close-form solutions of angular spectra and paraxial propagation of these beams were derived. These beams have asymmetric intensity distributions and carry the same orbit angular momentum per photon as the corresponding Bessel-Gauss beams. While propagating along z axis, the mth (m≠0) non-coaxial Bessel-Gauss beams rotate their intensity distributions and the mth-order vortex at the beam center have a transverse shift along the direction perpendicular to offset axis. Depending on the product of transverse scalar factor of Bessel beams and offset between Gaussian window function and the center of Bessel beams, the non-coaxial Bessel-Gauss beams can produce unit vortices with opposite signs in pairs during propagation.

Bias effects of short- and long-term color memory for unique objects

Marina Bloj, David WEIß, and Karl Gegenfurtner

Doc ID: 250827 Received 18 Dec 2015; Accepted 27 Jan 2016; Posted 29 Jan 2016  View: PDF

Abstract: Are objects remembered with a more saturated color? Some of the evidence supporting this statement comes from research using ‘memory colors’ – the typical colors of particular objects, for example the green of grass. The problematic aspect of these findings is that many different exemplars exist, some of which might exhibit a higher saturation than the one measured by the experimenter. Here we avoid this problem by using unique personal items and comparing long- and short-term color memory matches with those obtained with the object present. Our results, on average, confirm that objects are remembered as more saturated than they are.

Changes in unique hues induced by chromatic surrounds

Thomas Wachtler and Susanne Klauke

Doc ID: 251577 Received 08 Oct 2015; Accepted 26 Jan 2016; Posted 26 Jan 2016  View: PDF

Abstract: A chromatic surround can have a strong influence on the perceived hue of a stimulus. We investigated whether chromatic induction has similar effects on the perception of colors that appear pure and unmixed (unique red, green, blue, and yellow) as on other colors. Subjects performed unique hue settings of stimuli in isoluminant surrounds of different chromaticities. Compared to the settings in a neutral gray surround, unique hue settings were systematically altered with chromatic surrounds. The amount of induced hue shift depended on the difference between stimulus and surround hue, and was similar for unique hue settings as for settings of non-unique hues. Variabilities in unique hue settings were roughly twice as high than settings obtained in asymmetric matching experiments, which may reflect the presence of a reference stimulus in the matching task. Variabilities were also larger with chromatic surrounds than with neutral gray surrounds, for both unique hue settings and matching of non-uniqe hues. The results suggest that the neural representations underlying unique hue percepts are influenced by the same neural processing mechanisms as the percepts of other colors.

Development of an Ideal Observer that Incorporates Nuisance Parameters and Processed List-Mode Data

Christopher MacGahan, Matthew Kupinski, Erik Brubaker, Nathan Hilton, and William Johnson

Doc ID: 251858 Received 21 Oct 2015; Accepted 25 Jan 2016; Posted 26 Jan 2016  View: PDF

Abstract: Observer models were developed to process data in list-mode format in order to perform binary discriminationtasks for use in an arms-control-treaty context. Data used in this study was generated usingGEANT4 Monte Carlo simulations for photons using custom models of plutonium inspection objectsand a radiation imaging system. Observer model performance was evaluated and presented using thearea under the receiver operating characteristic curve. The ideal observer was studied under both signalknown-exactly conditions and in the presence of unknowns such as object orientation and absolute countratevariability; when these additional sources of randomness were present, their incorporation into theobserver yielded superior performance.

Singular Mueller matrices

Jose Gil, Razvigor Ossikovski, and Ignacio San José

Doc ID: 255952 Received 18 Dec 2015; Accepted 25 Jan 2016; Posted 26 Jan 2016  View: PDF

Abstract: Singular Mueller matrices play an important role in polarization algebra and have peculiar properties that stem from the fact that either the medium exhibits maximum diattenuation and/or polarizance, or because its associated canonical depolarizer has the property of fully randomizing, the circular component (at least) of the states of polarization of light incident on it. The formal reasons for which the Mueller matrix M of a given medium is singular are systematically investigated, analyzed and interpreted in the framework of the serial decompositions and the characteristic ellipsoids of M. The analysis allows for a general classification and geometric representation of singular Mueller matrices, of potential usefulness to experimentalists dealing with such media.

ExpressionsforparalleldecompositionoftheMüllermatrix

Colin Sheppard, Marco Castello, and Alberto Diaspro

Doc ID: 249674 Received 07 Sep 2015; Accepted 25 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: It is useful to convert between the Müller matrix and two different Hermitian matrices, representing an optical material or system, which are in the literature. We introduce explicit transformation matrices for converting the column vector forms of these different matrices. We find that there is no great advantage, from the point of view of matrix manipulation, in using the quantum mechanics ordering rather than the optical ordering of the Stokes parameters, as has been claimed elsewhere.

Unique hue correction applied to the color rendering of LED light sources

Pedro Pardo, Eduardo Cordero, Isabel Suero, and Angel Luis Perez

Doc ID: 249809 Received 02 Oct 2015; Accepted 24 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: Existing color quality indices for light sources provide broad information about different dimensions related withcolor quality. Color fidelity, harmony or gamut area are concepts related with these indices and industry requeststhis information. During the last years, LED light sources have been widely used at home and at work and now acolor rendering index that solves the problem of underestimation of this type of light sources is needed, to providea score of subjective assessment made by real observers related with color fidelity. In this work, this problem hasbeen studied in two ways: theoretically and experimentally and the results show discrepancies between the huecomposition calculated theoretically using a color appearance model and hue composition evaluated by realobservers. These discrepancies could originate divergences in the color fidelity score and the subjective evaluationof naturalness of a scene.

Low levels of specularity support operational color constancy when surface and illumination geometry can be inferred

Robert Lee and Hannah Smithson

Doc ID: 251243 Received 02 Oct 2015; Accepted 24 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: We tested whether surface specularity alone supports operational color constancy – the ability to discriminate changes in illumination or reflectance. Observers viewed short animations of illuminant or reflectance changes in rendered scenes containing a single surface, and were asked to classify the change. Performance improved with increasing specularity, as predicted from regularities in chromatic statistics. Performance was impaired by spatial rearrangements of image pixels that disrupted the perception of illuminated surfaces, but was maintained with increased surface complexity. The characteristic chromatic transformations that are available with non-zero specularity are useful for operational color constancy, particularly if accompanied by appropriate perceptual organisation.

Collaborative Multi-cue Fusion Using Cross DiffusionProcess for Salient Object Detection

Changxin Gao, Jin-Gang Yu, and Jinwen Tian

Doc ID: 254110 Received 16 Nov 2015; Accepted 24 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: Salient object detection is very useful in a large variety of image and vision related applications. A recenttrend in salient object detection is to explore novel top-down visual cues and combine them with bottomupsaliency to improve the performance. However, a basic and important problem, i.e., how to effectivelyfuse multiple visual cues, has rarely been addressed in previous works. To this end, the paper presentsa multi-cue fusion method using Cross Diffusion Process (CDP) for salient object detection. The CDPalgorithm is deployed to combine the affinity matrices constructed over individual visual cue channels,which is then embedded into a saliency propagation framework to accomplish salient object detection.Different from other multi-cue fusion strategies, our proposed approach allows for collaborative fusion,that is, the individual visual cues to be fused are able to interact and exchange information with eachother during the fusion procedure, which can possibly correct the noise or corruption included in theindividual visual cue channels, leading to more robust and effective fusion results. Intensive experimentson publicly available datasets demonstrate the effectiveness and superior performance of our proposedmethod.

Retrieval of refractive index fields in two-dimensional gradient-index elements from external deflectometry data

Di Lin and James Leger

Doc ID: 248969 Received 31 Aug 2015; Accepted 24 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: In a previous work, we presented a numerical method for retrieving inhomogeneous refractive index fields in rectangular gradient-index (GRIN) elements from boundary positions and internal boundary slopes associated with a set of interrogating probe beams that transits the medium. The present work extends this method to external boundary beam slopes without knowledge of the refractive index along the surface of the optical element. The inverse problem is cast as a linear algebraic system describing the deflection of probe beams inside the optical material and an iterative inversion algorithm is used to generate an index field that produces the boundary value data. By incorporating Snell’s law into the system equation through surface values derived from tentative reconstructions of the refractive index, we show in simulation that a series of inversion cycles applied to the system equation accurately recovers the index profile used to generate the test data.

Fast semi-analytical solution of Maxwell’s equations inBorn approximation for periodic structures

Maxim Pisarenco, Richard Quintanilha, Mark van Kraaij, and Wim Coene

Doc ID: 253278 Received 04 Nov 2015; Accepted 24 Jan 2016; Posted 02 Feb 2016  View: PDF

Abstract: We propose a fast semi-analytical approach for solving Maxwell’s equations in Born approximation basedon the Fourier modal method (FMM). We show that, as a result of the Born approximation, most of thematrices in the FMM algorithm become diagonal, thus allowing a reduction of computational complexityfrom cubic to linear. Moreover, due to the analytical representation of the solution in the vertical direction,the number of degrees of freedom in this direction is independent of the wavelength. The method isderived for planar illumination with two basic polarizations (TE/TM) and an arbitrary two-dimensionalgeometry infinitely periodic in one horizontal direction.

Orthogonality breaking sensing model by the instantaneous Stokes vector and the Mueller calculus

Noé Ortega-Quijano, Julien FADE, Muriel Roche, François PARNET, and Mehdi Alouini

Doc ID: 246794 Received 27 Jul 2015; Accepted 23 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: Polarimetric sensing by orthogonality breaking has been recently proposed as an alternative technique for performing direct and fast polarimetric measurements using a specific dual-frequency dual-polarization (DFDP) source. Based on the instantaneous Stokes-Mueller formalism to describe the high-frequency evolution of the DFDP beam intensity, we thoroughly analyze the interaction of such beam with birefringent, dichroic and depolarizing samples. This allows us to confirm that orthogonality breaking is produced by the sample diattenuation, whereas this technique is immune to both birefringence and diagonal depolarization. We further analyze the robustness of this technique when polarimetric sensing is performed through a birefringent waveguide, and the optimal DFDP source configuration for fiber-based endoscopic measurements is subsequently identified. Finally, we consider a stochastic depolarization model based on an ensemble of random linear diattenuators, which makes it possible to understand the progressive vanishing of the detected orthogonality breaking signal as the spatial heterogeneity of the sample increases, thus confirming the insensitivity of this method to diagonal depolarization. The fact that the orthogonality breaking signal is exclusively due to the sample dichroism is an advantageous feature for the precise decoupled characterization of such anisotropic parameter in samples showing several simultaneous effects.

Structure Tensor Based Automated Detection ofMacular Edema and Central Serous Retinopathy usingOptical Coherence Tomography Images

Bilal Hassan, Gulistan Raja, and Taimur Hassan

Doc ID: 254162 Received 19 Nov 2015; Accepted 23 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: Macular Edema (ME) and Central Serous Retinopathy (CSR) are the two macular diseases that affect the centralvision of a person if they are left untreated. Optical Coherence Tomography (OCT) imaging is the latest eyeexamination technique which shows the cross sectional region of retinal layers that can be used to detect manyretinal disorders in an early stage. Many researchers have done clinical studies about ME and CSR and reportedsignificant findings in macular OCT scans. However, this paper proposes an automated method for classification ofME and CSR from OCT images using Support Vector Machine (SVM) classifier. 5 distinct features (3 based onthickness profile of sub-retinal layers and 2 based on cyst fluid within sub-retinal layers) are extracted from 30labeled images (10 ME, 10 CSR and 10 healthy) on which SVM is trained. We applied our proposed algorithm on 90Time Domain OCT (TD-OCT) images (30 ME, 30 CSR, 30 Healthy) of 73 patients. Our algorithm correctly classified88 out of 90 subjects with accuracy, sensitivity and specificity of 97.77%, 100% and 93.33% respectively.

Two efficient approaches for modelling of Raman scattering in homogeneous turbid media

Ilya Krasnikov, CHRISTIAN SUHR, Alexey Seteikin, Bernhard Roth, and Merve Wollweber

Doc ID: 253828 Received 12 Nov 2015; Accepted 23 Jan 2016; Posted 25 Jan 2016  View: PDF

Abstract: The quantitative analysis of Raman spectroscopic signals in biological tissue is generally difficult. Typical samples contain a multitude of molecular species and, in addition, measurements are altered by attenuation of the Raman signal. Realistic numerical modelling of the Raman process can help to facilitate the quantitative analysis of the Raman spectra, but approaches so far are scarce and often time-consuming. In this work, we report on two different and very efficient approaches for modelling of Raman scattering in turbid media irradiated by laser light. Both approaches utilize the Monte Carlo method to simulate the Raman scattering process. We compare the efficiency of both approaches and discuss possible future extensions and experimental validation.

Partially-coherent contrast-transfer-function approximation

Yakov Nesterets and Timur Gureyev

Doc ID: 254340 Received 20 Nov 2015; Accepted 21 Jan 2016; Posted 01 Feb 2016  View: PDF

Abstract: The contrast-transfer-function (CTF) approximation, widely used in various phase-contrast imaging techniques, is revisited. CTF validity conditions are extended to a wide class of strongly absorbing and refracting objects as well as to non-uniform partially-coherent incident illumination. Partially-coherent free-space propagators, describing amplitude and phase in-line contrast, are introduced and their properties are investigated. The presented results are relevant to design of imaging experiments with partially-coherent sources, as well as to analysis and interpretation of the corresponding images.

Investigation of the moire patterns of defected radial and circular gratings using reciprocal vectors approach

Saifollah Rasouli and Mohammad Yeganeh

Doc ID: 253093 Received 02 Nov 2015; Accepted 20 Jan 2016; Posted 20 Jan 2016  View: PDF

Abstract: In this work, for the first time, an investigation on the moire patterns of superimpositions of two radial or two circular gratings consisting topological defects and their mutual superimpositions with each other or with linear forked gratings or defected zone plats is presented. For characterization of the resulting moire patterns, we use the reciprocal vectors approach. In this approach, by considering local spatial frequenciesfor the superimposed structures, their reciprocal vectors are determined from the transmission function of the structures. The local reciprocal vector of the resulting moire pattern at a given point is determined in terms of the local reciprocal vectors of the superimposed structures defined at the same point. In this approach, the topological singularities of the superimposed structures are described by the azimuthal component of the reciprocal vectors. This formulation is very simple, uniform, and comprehensive. In this work we offer detailed discussions on the different resulting moire patterns for the above-mentioned superimpositions and some potential applications of the proposed superimpositions are introduced. In addition, different resulting moire patterns are simulated.

A analytical model of the influence of cone sensitivity and numerosity on the Rayleigh match

Li Zhaoping and Joseph Carroll

Doc ID: 250942 Received 28 Sep 2015; Accepted 16 Jan 2016; Posted 19 Jan 2016  View: PDF

Abstract: The Rayleigh match is defined by the range of mixtures of red and green lights that appear the same as anintensity-adjustable monochromatic yellow light. The perceptual match indicates that the red/green mixture and the yellow lighthave evoked the same respective cone absorptions in the L- and M-cone pathways. Going beyond the existing models(e.g., Pokorny et al 1973, He \& Shevell, 1995; Thomas \& Mollon, 2004; Barbur et al 2008), the Poisson noise in cone absorptions is proposed to makethe matching proportion of red-green mixtures span a finite range, since any mixture in that range evokes cone absorptionsthat do not differ from those by a yellow light by more than the variations in the absorption noise. We derive a mathematicalformula linking the match midpoint or match range with the sensitivities and numerosities of the two cones.The noise-free, exact, matching point, close to the mid-point of the matching range, depends only on the L- and M-conesensitivities to each of the red, green, and yellow lights (these sensitivities in turn dependon the preferred wavelengths ($\lambda_{max}$) and optical densities of the cone pigments and the various pre-receptorretinal light filtering properties). Meanwhile, the matching range depends on both these cone sensitivitiesand the relative numerosity of the L- and M-cones. The model predicts that, in normal trichromats, all other thingsbeing equal, the match range is smallest when the ratio r between L and M cone densities is r=R^{-½} with R as the ratio betweenthe sensitivities of the L and M cones to the yellow light, i.e., when L and M cones are similarly abundant in typical cases,and as r departs from R^{-½} the match range increases by up to (e.g.) 2--3 fold (depending on R) when one cone type isabout 10 times as numerous as the other. Testing these model predictions requires either a large data set to identify theeffect of one factor (e.g., cone numerosity) while averaging out the effects of the other factors (e.g., cone sensitivities),or when all factors are known in a data set. A corollary of this prediction is that the matching ranges of normalfemale trichromats who are carriers of dichromacy (but not anomalous trichromacy) are likely to have alarger matching range than usual, particularly for the deutan carriers.In addition, the model predicts that in strong tetrachromats (whose four dimensions of color are preserved post-receptorally),the Rayleigh matching is either impossible or the matching range is typically smaller than usual.

Stimulus size dependence of hue changes induced by chromatic surrounds

Christian Kellner and Thomas Wachtler

Doc ID: 251587 Received 08 Oct 2015; Accepted 16 Jan 2016; Posted 19 Jan 2016  View: PDF

Abstract: A chromatic surround induces a change in the perceived hue of a stimulus. This shift in hue depends on the chromatic difference between stimulus and surround. We investigated how chromatic induction varies with stimulus size and whether the size dependence depends on the surround hue. Subjects per- formed asymmetric matching of color stimuli with different sizes in surrounds of different chromaticities. Generally, induced hue shifts decreased with increasing stimulus size. This decrease was quantitatively different for different surround hues. However, when size effects were normalized to overall induction strength, the chromatic specificity was largely reduced. The separability of inducer chromaticity and stim- ulus size suggests that these effects are mediated by different neural mechanisms.

Noise Robustness of a Combined Phase Retrieval and Reconstruction Method for Phase-Contrast Tomography

Rasmus Kongskov, Jakob Jørgensen, Henning Poulsen, and Per Christian Hansen

Doc ID: 249501 Received 04 Sep 2015; Accepted 15 Jan 2016; Posted 20 Jan 2016  View: PDF

Abstract: Classical reconstruction methods for phase-contrast tomography consist of two stages: phase retrieval and tomographic reconstruction. A novel algebraic method combining the two was suggested by Kostenko et al. (Opt. Express, 21, 12185, 2013) and preliminary results demonstrating improved reconstruction com- pared to a two-stage method given. Using simulated free-space propagation experiments with a single sample-detector distance, we thoroughly compare the novel method with the two-stage method to address limitations of the preliminary results. We demonstrate that the novel method is substantially more robust towards noise; our simulations point to a possible reduction in counting times by an order of magnitude.

Near- and far-field scattering resonances frequency shift in dielectric and PEC cylinders

Alex Yuffa, Yael Gutierrez, Juan Sanz, Rodrigo alcaraz, Jose Saiz, Francisco González, Fernando Moreno, and Gorden Videen

Doc ID: 255504 Received 09 Dec 2015; Accepted 13 Jan 2016; Posted 20 Jan 2016  View: PDF

Abstract: The ability to infer near-field scattering properties from far-field measurements is of paramount importance in nano-optics. Recently, we derived an approximate formula for predicting the frequency shift between near- and far-field intensity peaks in the case of a dielectric sphere. In this work, we demonstrate that almost an identical formula can be used to predict the resonance shift of a dielectric cylinder and a perfectly conducting cylinder. We find the redshift of the resonance peak of the perfect electric conducting (PEC) cylinder to be approximately two orders of magnitude greater than for the dielectric cylinder. The errors in our approximate analytic formula for predicting the redshift are only approximately twice as great. Furthermore, we apply the redshift formula to a silicon cylinder and discuss its magneto-dielectric properties, which may be of interest in design of metamaterials.

Particle Filter based Phase Estimation in Digital Holographic Interferometry

Rahul Waghmare, Sai Subrahmanyam Gorthi, Deepak Mishra, Rakesh Singh, and Pothuri Ram Sukumar

Doc ID: 251863 Received 13 Oct 2015; Accepted 12 Jan 2016; Posted 13 Jan 2016  View: PDF

Abstract: In this article, we propose a Particle Filter based technique for the analysis of reconstructed interference field. Particle filter and its variants are well proven as tracking filters in non-Gaussian and non-linear situations. We propose to apply the particle filter for direct estimation of phase and its derivatives from digital holographic interferometric fringes via signal tracking approach on a Taylor series expanded state model and polar to Cartesian conversion based measurement model. Computation of sample weights through non-Gaussian likelihood forms the major contribution of the proposed particle filter based approach compared to the existing Unscented Kalman Filter based approach. It is observed that the proposed approach is highly robust to noise and outperforms the state-of-the-art especially at very low Signal to Noise ratio (i.e., especially in the range of -5 dB to 20 dB). The proposed approach, to the best of our knowledge, is the only method available for phase estimation from severely noisy fringe patterns even when the underlying phase patterns is rapidly varying and having larger dynamic range. Simulation results and experimental data demonstrates the fact that the proposed approach is a better choice for direct phase estimation.

Light transport in refractive turbid media

Vadim Soloviev

Doc ID: 252484 Received 22 Oct 2015; Accepted 11 Jan 2016; Posted 12 Jan 2016  View: PDF

Abstract: Light scattering in refractive media can be used for visualization of caustics and singularities of wave fronts of the incident radiation. Its modeling requires solving the radiative transfer equation. Numerical solution of the radiative transfer equation in turbid media with a spatially varying refractive index is presented and discussed in this paper. The approach is based on the self-consistent approximation of the RTE and results in relatively inexpensive and robust numerical algorithm. Simulations are presented for several cases including a weakly scattering medium with varying refractive index and a refractive weakly scattering medium with embedded highly scattering objects.

Segregating animals in naturalistic surroundings: Interaction of color distributions and mechanisms.

michael jansen, Qasim Zaidi, and Martin Giesel

Doc ID: 251227 Received 01 Oct 2015; Accepted 10 Jan 2016; Posted 13 Jan 2016  View: PDF

Abstract: Humans have been shown to rapidly detect animals in naturalistic scenes, but the role of color in this task is unclear. We first analyze the color information contained in a large number of images of salient and camouflaged animals. We found that color distributions of most animals and of their immediate backgrounds were oriented along other than the cardinal directions of color space. In addition, the maximum distances between animal and background distributions also tended to be along non-cardinal directions, suggesting a role for higher-order cortical color mechanisms whose preferred axes are distributed widely in color space. We measured temporal thresholds for segmenting animal color distributions from background distributions in the absence of spatial cues. Thresholds for segmenting isoluminant projections of these distributions were sometimes lower than for segmenting the original distributions, and considerably lower than for segmenting achromatic projections. Color information is thus likely to be useful in segregating animals in generic views, i.e. views not purposely chosen by the photographer to enhance the visibility of the animal. However, a comparison of thresholds with distances between distributions failed to reveal any advantage conferred by higher-order color mechanisms.

Metamer Mismatching in Practice versus Theory

Xiandou Zhang, Brian Funt, and Hamidreza Mirzaei

Doc ID: 251604 Received 08 Oct 2015; Accepted 10 Jan 2016; Posted 11 Jan 2016  View: PDF

Abstract: Metamer mismatching (the phenomena that two objects matching in color under one illuminant may not match under a different illuminant) potentially has important consequences for color perception. Logvinenko et al. [1] show that in theory the extent of metamer mismatching can be very significant. This paper examines metamer mismatching in practice by computing empirical metamer mismatch bodies and comparing them to the theoretical mismatch bodies. A set of more than 40 million unique reflectance spectra is assembled using datasets from several sources. For a given color signal (i.e., CIE XYZ, cone LMS, or camera RGB) recorded under a given first illuminant, its empirical metamer mismatch body for a change to a second illuminant is computed as follows: the reflectances having the same color signal when lit by the first illuminant (i.e., reflect metameric light) are computationally relit by the second illuminant and the convex hull of the resulting color signals then defines the empirical metamer mismatch body. The volume of these bodies is shown to vary systematically with Munsell value and chroma. The empirical mismatch bodies are compared to the theoretical mismatch bodies computed using the algorithm of Logvinenko et al. [2]. There are three key findings: (1) The empirical bodies are found to be substantially smaller than the theoretical ones; (2) The sizes of both the empirical and theoretical bodies show a systematic variation with Munsell value and chroma; (3) Applied to the problem of color-signal prediction, the centroid of the empirical metamer mismatch body is shown to be a better predictor of what a given color signal might become under a specified illuminant than state-of-the-art methods.

Propagation properties of a radially polarized partiallycoherent twisted beam in free space

Gaofeng Wu

Doc ID: 252291 Received 21 Oct 2015; Accepted 10 Jan 2016; Posted 11 Jan 2016  View: PDF

Abstract: We introduce a radially polarized partially coherent twisted (RPPCT) beam based on the unified theoryof coherence and polarization. We also derive expressions of this beam propagating in free space andexamine the influence of twist factor and coherence of source plane on its propagation properties. It isfound that both twist factor and coherence of source plane affect its average intensity, polarization andcoherence. Those results also show the beam is rotating with beam propagation and the beam’s rotationis independent of coherence of source plane.

Shannon information for joint estimation/detection tasks and complex imaging systems

Johnathan Cushing and Eric Clarkson

Doc ID: 251261 Received 02 Oct 2015; Accepted 05 Jan 2016; Posted 05 Jan 2016  View: PDF

Abstract: Shannon information is defined for imaging tasks where signal detection is combined with parameterestimation. The first task considered is when the parameters are associated with thesignal and parameter estimates are only produced when the signal is present. The second taskexamined is when the parameters are associated with the object being imaged, and parametersestimates are produced whether the signal is present or not. In each case the Shannoninformation expression has a simple additive form.

The role of extrinsic noise in the sensitivity of the rod pathway; rapid dark adaptation of nocturnal vision in humans.

Adam Reeves and rebecca grayhem

Doc ID: 249846 Received 10 Sep 2015; Accepted 05 Jan 2016; Posted 05 Jan 2016  View: PDF

Abstract: Rod-mediated test spots were flashed in Maxwellian view at 5deg eccentricity, both on steady 10.4deg fields of intensities (I) from 0.00001 to 1 sc td and from 0.2s to 1s after extinguishing the field. On dim fields, thresholds of tiny (5’) tests were proportional to √I (Rose-DeVries law), while thresholds after extinction fell within 0.6s to the fully dark-adapted absolute threshold. Thresholds of large (1.3deg) tests were proportional to I (Weber law) and extinction thresholds, to √I. Conclusions: rod thresholds are elevated by photon-driven noise from dim fields that disappears at field extinction; large spot thresholds are additionally elevated by neural light adaptation proportional to √I. At night, recovery from dimly lit fields is typically fast, not slow.

Change Detection in Underwater Imagery

karthik seemakurthy and Ambasamudram Rajagopalan

Doc ID: 250634 Received 25 Sep 2015; Accepted 03 Jan 2016; Posted 05 Jan 2016  View: PDF

Abstract: In this work, we deal with the problem of change detection in underwater scenario given an unblurred-blurred image pair of a planar scene taken at different instants of time. The blur is primarily due to thedynamic nature of water surface and its nature is space-invariant in the presence of cyclic water flows. Exploiting the sparsity of the induced blur as well as the occlusions, we propose a distort-difference pipelinethat employs an alternating minimization framework to perform change detection in the presence of geometric distortions (skew) as well as photometric degradations (blur and illumination variations). Themethod can effectively yield both sharp and blurred occluder maps. Using synthetic as well as real data, we demonstrate how the proposed technique advances the state-of-the-art.

Effects of surrounding stimulus properties on color constancy based on luminance balance

Takuma Morimoto, Kazuho Fukuda, and Keiji Uchikawa

Doc ID: 250930 Received 30 Sep 2015; Accepted 01 Jan 2016; Posted 05 Jan 2016  View: PDF

Abstract: The visual system needs to discount the influence of an illuminant to achieve color constancy. Uchikawa et al. (2012) showed that the luminance-balance change of surfaces in a scene contributes to estimating an illuminant in the scene, but its effect was substantially smaller than chromaticity change. The present study conducted three experiments aiming at reinforcing the previous findings and revealing the possible reason of the smaller effect of the luminance-balance. Results confirmed the luminance-balance plays an important role to estimate an illuminant in the scene where chromaticities of all surfaces are the same across illuminants. Also, unlike chromaticity-based color constancy, chromatic variation does not influence the effect of the luminance-balance. Moreover, it was shown that the luminance-balance based estimation of an illuminant performs better when scene has reddish or bluish surfaces. These suggested that visual system exploits the optimal color distribution to estimate an illuminant. K. Uchikawa, K. Fukuda, Y. Kitazawa, and D. I. A. MacLeod, “Estimating illuminant color based on luminance balance of surfaces,” J. Opt. Soc. Am. A, 29, 133-143 (2012)

Perception of saturation in natural scenes

Karl Gegenfurtner and Florian Schiller

Doc ID: 251193 Received 02 Oct 2015; Accepted 31 Dec 2015; Posted 05 Jan 2016  View: PDF

Abstract: We measured how well perceived color saturation when viewing natural scenes can be predicted by different measures that are available in the literature. We presented 80 color images of natural scenes or their grayscale counterparts to our observers, who were asked to choose the pixel from each image that appeared to be the most saturated. We compared our observers' choices to the predictions of seven popular saturation measures. For the color images, all of the measures predicted perception of saturation quite well, with CIECAM02 performing best. Differences between the measures were small but systematic. When grayscale images were viewed, observers still chose pixels whose counterparts in the color images were saturated above average. This indicates that image structure and prior knowledge can be relevant to perception of saturation. Nevertheless, our results also show that saturation in natural scenes can be specified quite well without taking these factors into account.

Phase shift effect of amplitude spread function on spectrum and image formation in coherent Raman scattering microspectroscopy

Naoki Fukutake

Doc ID: 251904 Received 15 Oct 2015; Accepted 31 Dec 2015; Posted 05 Jan 2016  View: PDF

Abstract: Coherent Raman scattering microspectroscopy, which includes coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microspectrpscopy, permits label-free hyperspectral imaging. We report the theoretical study of the phase-shift effect of the impulse response function on the spectral and image-forming properties of coherent Raman scattering microspectroscopy. We show that the spectrum and image are influenced by not only the NA of objective for excitation (NAex) but also that for signal collection (NAcol), in association with the phase-shift effect. We discuss that under the condition NAex≠NAcol, both the spectrum and the image become deformed by the phase-shift effect, which can be applied to the direct measurement of the imaginary part of the nonlinear susceptibility in CARS spectroscopy. We point out that even in SRS microscopy, the nonresonant background can contribute to the image formation and cause the artifact in the image.

Reflection of diffuse light from dielectric one-dimensional rough surfaces

Eugenio Mendez, Alma González-Alcalde, Emiliano Teran, Fabio Cuppo, Jose Alberto Olivares, and Augusto Garcia-Valenzuela

Doc ID: 251056 Received 29 Sep 2015; Accepted 30 Dec 2015; Posted 05 Jan 2016  View: PDF

Abstract: We study the reflection of diffuse light from one-dimensional, randomly rough dielectric interfaces. Resultsfor the reflectance under diffuse illumination are obtained by rigorous numerical simulations andcontrasted with those obtained for flat surfaces. We also explore the possibility of using perturbationtheories and conclude that they are very limited for this kind of studies. Numerical techniques basedon the Kirchhoff approximation and the reduced Rayleigh equations yield better results. We find that,depending on the refractive index contrast and the nature of the irregularities, the roughness can increaseor decrease the diffuse reflectance of the surface.

Effective impedance modeling of metamaterial structures

Kokou Dossou, Chris Poulton, and Lindsay Botten

Doc ID: 251592 Received 08 Oct 2015; Accepted 29 Dec 2015; Posted 05 Jan 2016  View: PDF

Abstract: We present methods for retrieving the effective impedance of metamaterials from the Fresnel reflection coefficients at the interface between two semi-infinite media.The derivation involves the projection of rigorous modal expansions onto the dominant modes of the two semi-infinite media.It is shown that the effective impedance can also be written as ratio of averaged field quantities.Thus a number of effective impedance formulas, previously obtained by field averaging techniques, can also be derived from the scattering-based formalism, by an appropriate choice of projection.Within the effective medium limit, it is observed that a simple semi-analytic modelling technique based on the effective impedancecan be used to reliably compute the reflection coefficients of metamaterials over a wide range of incidence angles.We use this technique to model planar metamaterial waveguides or surface modes.

A dim view of M-cone onsets

Neil Parry, Declan McKeefry, Jan Kremers, and Ian Murray

Doc ID: 250765 Received 01 Oct 2015; Accepted 27 Dec 2015; Posted 05 Jan 2016  View: PDF

Abstract: We investigated the brightness (i.e. perceived luminance) of isolated L- and M-cone pulses, to seek a perceptualcorrelate of our previous reports that M-on electroretinograms resemble L-off responses, implying the operation ofpost-receptoral opponent processing. Using triple silent substitutions, cone increments were generated in a 4-primary ganzfeld, masked by random positive or negative luminance bias. The results show that M-coneincrements decrease in brightness, whilst L-cone increments increase. These differences became smaller as fieldsize reduced; this was not eccentricity or area dependent. We speculate about early retinal input into brightnessperception.

Is discrimination enhanced at a category boundary? The case of unique red

Marina Danilova and John Mollon

Doc ID: 251230 Received 01 Oct 2015; Accepted 23 Dec 2015; Posted 24 Dec 2015  View: PDF

Abstract: Is chromatic discrimination enhanced at the boundary between different hues? In previous studies we have given a positive answer for the case of the locus of unique blues and yellows, the boundary that divides color space into reddish and greenish hues. But we did not find enhancement at the locus of unique green, the boundary between yellowish and bluish hues. In the present study we examined discrimination near the locus of unique red. In interleaved experimental runs, we measured chromatic discrimination using a four-alternative spatial forced choice and we measured the locus of unique red by means of phenomenological judgments. When the locus of unique red was traversed along -45° lines in a MacLeod-Boynton diagram, the locus of minimal thresholds coincided approximated with the locus of the equilibrium hue; but this was not the case when the unique red locus was traversed in +45° direction. To account for these several results, we suppose that the neural channel that determines the discrimination threshold will sometimes coincide with the channel that determines the perceptual hue equilibrium, and sometimes will not. If a given point in chromaticity space is a unique hue, then it is expected to remain a unique hue independently of the direction in which measurements are made; but discrimination thresholds almost certainly will depend on different underlying channels when measurements at made in different directions through the same point in chromaticity space.

Eye centre localisation and gaze gesture recognition for human computer interaction

WENHAO ZHANG, Melvyn Smith, Lyndon Smith, and Abdul Farooq

Doc ID: 246605 Received 24 Jul 2015; Accepted 21 Dec 2015; Posted 22 Dec 2015  View: PDF

Abstract: This paper introduces an unsupervised modular approach for accurate and real-time eye centre localisation in images and videos following a coarse-to-fine, global-to-regional scheme. The trajectories of eye centres in consecutive frames, i.e. gaze gestures, are further analysed, recognised and employed to boost human computer interaction (HCI) experience. This modular approach makes use of isophote and gradient features to estimate the eye centre locations. A Selective Oriented Gradient (SOG) filter has been specifically designed to remove strong gradients from eyebrows, eye corners and shadows, which sabotage most eye centre localisation methods. A real-world implementation utilising these algorithms has been designed in the form of an interactive advertising billboard to demonstrate the effectiveness of our method for HCI. The eye centre localisation algorithm has been compared with 10 other state-of-the-art algorithms and has outperformed all the other algorithms in comparison in terms of localisation accuracy. Further tests on self-collected data have proved this algorithm to be robust against head poses and poor illumination conditions. The interactive advertising billboard has manifested outstanding usability and effectiveness in our tests, which shows great potential in benefiting a wide range of real-world HCI applications.

Gender recognition from facial images: 2D or 3D?

WENHAO ZHANG, Melvyn Smith, Lyndon Smith, and Abdul Farooq

Doc ID: 245746 Received 17 Jul 2015; Accepted 13 Dec 2015; Posted 18 Dec 2015  View: PDF

Abstract: This paper seeks to compare encoded features from both 2D and 3D face images in order to achieve automatic gender recognition withhigh accuracy and robustness. The Fisher Vector encoding method is employed to produce 2D, 3D and fused features with escalateddiscriminative power. For 3D face analysis, a two-source Photometric Stereo (PS) method is introduced that enables 3D surfacereconstructions with accurate details as well as desirable efficiency. Moreover, a 2D+3D imaging device, taking the two-source PS methodas its core, has been developed that can simultaneously gather colour images for 2D evaluations and PS images for 3D analysis. This systeminherits the superior reconstruction accuracy from the standard (3 or more light) PS method, but simplifies the reconstruction algorithm aswell as the hardware design by only requiring two light sources. It also offers great potential for facilitating human computer interaction bybeing accurate, cheap, efficient and non-intrusive.10 types of low-level 2D and 3D features have been experimented with and encoded for Fisher Vector gender recognition. Evaluations ofthe Fisher Vector encoding method have been performed on the FERET database, Colour FERET database, LFW database and FRGCv2database, yielding 97.7%, 98.0%, 92.5% and 96.7% accuracy, respectively. In addition, the comparison of 2D and 3D features has beendrawn from a self-collected dataset, which is constructed with the aid of the 2D+3D imaging device in a series of data capture experiments.With a variety of experiments and evaluations, it can be proved that the Fisher Vector encoding method outperforms most state-of-the-artgender recognition methods. It has also been observed that 3D features reconstructed by the two-source PS method are able to furtherboost the Fisher Vector gender recognition performance, i.e. up to a 6% increase on the self-collected database.

Radiative transport and optical tomography with large data sets

Manabu Machida, George Panasyuk, Zheng-Min Wang, Vadim Markel, and John Schotland

Doc ID: 250385 Received 21 Sep 2015; Accepted 16 Nov 2015; Posted 11 Dec 2015  View: PDF

Abstract: We consider the inverse problem of optical tomography in the radiative transport regime. We report numerical tests of a direct reconstruction method that is suitable for use with large data sets. Reconstructions of experimental data obtained from a noncontact optical tomography system are also reported.

(CV) Independence and interaction of luminance and chromatic contributions to spatial hyperacuity performance

Bonnie Cooper and Barry Lee

Doc ID: 198653 Received 30 Sep 2013; Accepted 02 Feb 2014; Posted 03 Feb 2014  View: PDF

Abstract: Here we test interactions of luminance and chromatic input to spatial hyperacuity mechanisms. First, we tested alignment with matching or mismatching (contrast polarity or modality) grating pairs that were adjusted to detection threshold. Thresholds with mismatched pairs were significantly elevated. Second, we determined alignment acuity as a function of luminance or chromatic contrast alone or in the presence of contrast pedestals. For in-phase pedestal conditions, performance followed the envelope of the more sensitive mechanism. However, polarity reversals revealed an asymmetric effect for luminance and chromatic conditions. This suggests that luminance can overrule chromatic mechanisms in hyperacuity; we interpret these findings in the context of spatial mechanisms.

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