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Accurate wavelength calibration method for compact CCD-spectrometer

Yanchao Sun, Guo Xia, Chan Huang, Shiqun Jin, and hongbo lu

Doc ID: 283742 Received 28 Dec 2016; Accepted 17 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: Wavelength calibration is an important step in CCD-spectrometer. In this paper, an accurate calibration method is proposed. A model of line profile spectrum is built at the beginning, followed by noise reduction, bandwidth correction and automatic peak-seeking treatment. Experimental tests are conducted on USB4000 spectrometer with mercury-argon calibration light source. Compared with the traditional method, the results show that this wavelength calibration procedure obtains higher accuracy and the deviations are within 0.1nm.

Wave-Amplitude Synthesis Applied to Gaussian-Beam Scattering by an Off-Axis Sphere

Dimitrios Chrissoulidis and Elodie Richalot

Doc ID: 281458 Received 23 Nov 2016; Accepted 15 Feb 2017; Posted 16 Feb 2017  View: PDF

Abstract: Electromagnetic scattering of a Gaussian beam by an off-axis dielectric sphere is treated by the sum-of-waves formulation which is inherent in Lorenz-Mie theory. Each “wave" is a spherical eigenvector, defined in the natural frame of the scatterer, and the coefficient of that wave is the “wave amplitude."Decomposition of the beam into homogeneous plane waves lays the ground for a synthesis of the wave amplitudes, which is done by an integration over the polar angle that defines the direction of propagation of the plane-wave constituents of the beam. Concise analytical results are developed for (a) the electric-field intensity in every part of space, (b) the bistatic and monostatic radar cross sections of the scatterer, and (c) the power extracted from the beam by scattering and absorption. Numerical calculations are made for a spherical glycerol droplet of radius 1.5um that is excited by an adjacent, infrared, Gaussian beam of wavelength 1.1424um and spot size 2um. The numerical application manifests (a) how the beam is coupled with the droplet and (b) the effect of the droplet on the power intercepted by a receiver-end fibre placed on the beam axis, beyond the focal plane. Comparisons to numerical results obtained by a FEM software (a) validate the sum-of-waves theory, (b) evaluate the performance of the code implementing that theory, and, succinctly, (c) manifest the limits of the plane-wave decomposition of the beam.

GREAT: A Gradient-based Color Sampling Scheme for Retinex

Michela Lecca, Alessandro Rizzi, and Raul Paolo Serapioni

Doc ID: 279301 Received 24 Oct 2016; Accepted 15 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: Modeling the local color spatial distribution is a crucial step for the algorithms of the Milano-Retinex family. Here we present GREAT, a novel, noise free Retinex implementation, based on an image aware spatial color sampling. As a member of the Retinex family, GREAT processes the chromatic channels of an input RGB image separately and outputs a new color image, said {\em color filtering}, which is a qualitative estimate of the human color sensation. For each channel, GREAT computes a 2D set of edges whose magnitude exceeds a pre-defined threshold. Then GREAT re-scales the chromatic intensity of each image pixel, said target, by the average of the intensities of the selected edges, weighted by a function of their positions, gradient magnitudes and intensity relative to the target. In this way, GREAT enhances the input image, adjusting its brightness, contrast and dynamic range. The use of the edges as pixels relevant to color filtering is justified by the importance that edges play in human color formation.The name GREAT comes from the expression "Gradient RElevAnce for reTinex", that refers to the threshold-based definition of a gradient relevance map for the edge selection and thus for the estimation of the color filtering.

Transformation of a High-dimensional Colour Space for Material Classification

Huajian Liu, Sang-heon lee, and Javaan Chahl

Doc ID: 279565 Received 27 Oct 2016; Accepted 15 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: Images in red-green-blue (RGB) colour space need to be transformed to other colour space for image processing or analysis. E.g., the well-known hue-saturation-intensity (HSI) colour space, which is similar to the colour perception of humans, can aid many computer vision applications. Some birds are tetrachromatic or pentachromatic and their visual systems can sense ultraviolet besides visible light. Similar to humans, the brain of birds might transform the optical signals received to a colour perception of hue, saturation and intensity. Inspired by this fact, the transformation of multispectral or hyperspectral images to a colour space which can separate ‘hue’ from saturation and intensity would be useful computer vision, however, the related works are limited. Some methods can transform hyperspectral images to new colour spaces which are for displaying or human observation, however, most of them usually need dimension reduction which could cause loss or distortion of original data, and therefore the transformed colour spaces are not suitable for material classification. This paper describes a method which can transform high-dimensional images to a colour space called hyper-hue-saturation-intensity (HHSI) which is analogous to HSI in high dimensions. The transformation does not need dimension reduction and therefore it can preserve the original information. Experimental results showed that the hyper-hue is independent of saturation and intensity and it is more suitable for material classification of proximal or remote sensing images of natural environment where illumination is usually out of control.

Cavity-backed metasurface antennas and their application to frequency diversity imaging

Daniel Marks, Okan Yurduseven, and David Smith

Doc ID: 281777 Received 29 Nov 2016; Accepted 13 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: Frequency diversity antennas with spatially structured radiation patterns reduce the reliance on actively switched elements for beamforming which become increasingly expensive and impractical as frequency increases. As the quality factor Q of a frequency diverse antenna increases, the antenna samples more spatial structure as the number of unique radiated coded spatial patterns correspondingly increases. Antennas that combine hollow cavities and metamaterial apertures achieve both large fractional bandwidth, in excess of 40%, and a high Q of 1600, so that each antenna radiates over 640 unique coded patterns. As compared to switched active antennas, such a passive antenna replaces the 50 antennas and switches that would produce at most (50/2)^2=625 unique patterns. Furthermore, the engineered metamaterial apertures enable a radiation efficiency exceeding 60% to be achieved in a single desired polarization. The theory of cavity-backed metasurface antennas is explained, and frequency diverse imaging is demonstrated with a pair of these antennas.

High performance analysis of layered nanolithography masks by a surface impedance generating operator

Alireza Gholipour, Reza Faraji-Dana, and Guy Vandenbosch

Doc ID: 279075 Received 26 Oct 2016; Accepted 12 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: A fast computational algorithm is presented for the analysis of multilayered nanolitography masks (M-NLM). The technique used is an exact field-theoretical approach which can model the diffraction effects in subwavelength propagation regimes. The field scattered by the mask pattern is obtained in two steps. First a surface impedance generating operator (SIGO) that relates the tangential electric field on the boundary of each etched area to its equivalent surface electric current is computed. Second the exterior problem is formulated based on the equivalence theorem in electromagnetics and is combined with the SIGO model. These two steps may be executed in parallel, making the lithography simulation fast and numerically efficient. For an arbitrary 2D mask illuminated by a TMy-polarized incident wave, the required Green's functions are obtained. The Green's function of the interior problem is calculated directly in spatial domain while the complex images method is used for computing the Green's functions of the exterior multilayer problem. Based on this forward modeling procedure, a parameter sweep is performed and a binary mask pattern under normal incident coherent illumination is analyzed.

Optical performance characterisations of light-logging actigraphy dosimeters

Luke Price, Andrey Lyachev, and Marina Khazova

Doc ID: 280192 Received 10 Nov 2016; Accepted 10 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: There are several wearable products specially developed or marketed for studying sleep, circadian rhythms and light levels. However, new recommendations relating to human physiological responses to light have changed what measurements researchers may demand. The performance of eleven light-logging dosimeters from eight manufacturers were compared. The directional and spectral sensitivities, linearity, dynamic range and resolution were tested for seven models, and compared along with other published data. The sample mainly comprised light-logging actigraphy dosimeters wearable as badges, in accordance with measurement protocols for larger scale field studies. A proposed standard for optical performance assessments is set out.

The spectral shift of light wave on scattering fromellipsoidal particle with arbitrary orientation

Zhimin Shi, Tao Wang, Darrick Hay, and Hao Wu

Doc ID: 282941 Received 15 Dec 2016; Accepted 10 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: Within the accuracy of the first-order Born approximation, a general expression for the far-zone spectrum of a light wave on scattering from an arbitrarily-orientated ellipsoidal particle is derived. We show that the spectrum of the scattered field, in general, changes with the scattering azimuthal angle, displaying rotational non-symmetry. The influence of the orientation of the particle on the spectrum of the scattered field is discussed, and the relationship between the orientation of scattering particle and the distribution of the relative spectral shift of the scattered field is investigated.

Fractal and spinodal-decomposed turbidities of nanoporous glass: Fluctuation picture in turbid and transparent Vycor

Shigeo Ogawa and Jiro Nakamura

Doc ID: 275751 Received 12 Sep 2016; Accepted 10 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: The light propagation and scattering in monolithic transparent nanoporous materials such as Vycor glasses exhibittwo optical turbidities, both of which are slightly deviated from the λ−4 Rayleigh wavelength dependence in thevisible (Vis) region: one is a transient white turbidity f τ , characterized by the convex-upward dependence on theinverse fourth power of wavelength, and the other is turbidity sp τ inherent to the structural inhomogeneity,characterized by the convex-downward dependence. The former is attributed to a fractal-like percolation networkof imbibed or drained pores as a consequence of transient imbibition or drainage of wetting fluid into or from thepore space. The latter is attributed to the structural inhomogeneities inherent to the original dry porous glass,which is produced by spinodal decomposition. In this paper, we develop a general scheme to estimate thetransmittance spectra of Vycor through the turbidities f τ and sp τ in the visible region on the basis of the theory ofdielectric constant fluctuations. We show that the applicability and its limitation of the turbidity analysis of thephotospectroscopically measured data as a method to study the correlation functions that characterize the porespace and the structural features of isotropic transparent nanoporous media, on the presupposition that thereexists no light attenuation other than the scattering.

Generalization of the Minkwitz Theorem to Non-Umbilical Lines of Symmetrical Surfaces

Gregor Esser, Wolfgang Becken, Helmut Altheimer, and Werner Müller

Doc ID: 281950 Received 01 Dec 2016; Accepted 06 Feb 2017; Posted 08 Feb 2017  View: PDF

Abstract: The linear relation between the increase of peripheral astigmatism and the increase of power along an umbilical line wasdescribed by Minkwitz and is known as the “Minkwitz Theorem”. However, in many cases, modern progressive addition lensesdo not show an umbilical principal line. Therefore, we propose to extend the Minkwitz Theorem to non-umbilical lines andhigher order terms than the linear term of the increase in the peripheral astigmatism. We were able to derive a “GeneralizedMinkwitz Theorem” which holds true for a prescribed astigmatism at the principal line. The derived Generalized MinkwitzTheorem also indicates that the increase of the astigmatism perpendicular to the principal line not only depends on the powerincrease, as described by the “Minkwitz Theorem”, but also on the astigmatism increase along the principal line. The “MinkwitzTheorem” itself is a special case of this generalization.

Interaction of aberrations, diffraction, and quantal fluctuations determine the impact of pupil size on visual quality

Renfeng Xu, Huachun Wang, Larry Thibos, and Arthur Bradley

Doc ID: 279244 Received 20 Oct 2016; Accepted 06 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Purpose: To develop a computational approach that jointly assesses the impact of stimulus luminance and pupil size on visual quality. Methods: We compared traditional optical measures of image quality and those that incorporate the impact of retinal illuminance dependent neural contrast sensitivity. Visually-weighted image quality was calculated for a presbyopic model eye with representative levels of chromatic and monochromatic aberrations as pupil diameter was varied from 7mm to 1mm, stimulus luminance varied from 2000 to 0.1 cd/m2 and defocus varied from zero to -2 diopters. The model included the effects of quantal fluctuations on neural contrast sensitivity. We tested the model’s predictions for 5 cycles per degree gratings by measuring contrast sensitivity at 5 cyc/deg. Results: Unlike the traditional Strehl Ratio and the visually-weighted area under the modulation transfer function, the visual Strehl Ratio derived from the optical transfer function was able to capture the combined impact of optics and quantal noise on visual quality. In a well-focused eye, provided retinal illuminance is held constant as pupil size varies, visual image quality scales approximately as the square root of illuminance because of quantum fluctuations, but optimum pupil size is essentially independent of retinal illuminance and quantum fluctuations. Conversely, when stimulus luminance is held constant (and therefore illuminance varies with pupil size), optimum pupil size increases as luminance decreases, thereby compensating partially for increased quantum fluctuations. However, in the presence of -1 and -2 diopters of defocus and at high photopic levels where Weber’s law operates, optical aberrations and diffraction dominate image quality and pupil optimization. Similar behavior was observed in human observers viewing sinusoidal gratings. Conclusions: Optimum pupil size increases as stimulus luminance drops for the well-focused eye, and the benefits of small pupils for improving defocused image quality remain throughout the photopic and mesopic ranges. However, restricting pupils to <2mm will cause significant reductions in the best focus vision at low photopic and mesopic luminances.

Theoretical analyses of liquid crystal adaptive lens with optically hidden dielectric double layer

Tigran Galstian, Oleksandr Sova, and Victor Reshetnyak

Doc ID: 282380 Received 07 Dec 2016; Accepted 31 Jan 2017; Posted 01 Feb 2017  View: PDF

Abstract: In this work we theoretically analyze the performance trends of a liquid crystal lens based on the optically hidden dielectric double layer principle. We demonstrate possible optimization ways of the lens versus the material and geometric parameters used. The impact of relative dielectric constants, conductivities and dimensions of the hidden dielectric layer’s components as well as the thickness and the temperature of the liquid crystal material are demonstrated. Corresponding trade-offs are briefly discussed.

A historical revision of the differential Stokes-Mueller formalism: discussion

Oriol Arteaga

Doc ID: 281336 Received 21 Nov 2016; Accepted 30 Jan 2017; Posted 31 Jan 2017  View: PDF

Abstract: The differential Stokes-Mueller matrix formalism expresses the local evolution of the Mueller matrix or the Stokes parameters for light propagating through a homogeneous optical medium. This manuscript presents a historical revision of the development of the differential Stokes-Mueller matrix formalism and highlights several important early contributions that have been overlooked. Particularly relevant is that this formalism was pioneered as early as 1929 by Paul Soleillet, almost 50 years earlier than it has been usually assumed. This historical revision demonstrates that several different authors independently formulated the differential Stokes-Mueller formalism during the XXth century and they found equivalent results studying the propagation problem from different approaches.

Correction of turbulence-degraded underwater images using shift map analysis

Kalyan Halder, Manoranjan Paul, Murat Tahtali, Sreenatha Anavatti, and Manzur Murshed

Doc ID: 278065 Received 03 Oct 2016; Accepted 12 Dec 2016; Posted 13 Dec 2016  View: PDF

Abstract: In underwater imaging, the water waves cause severe geometric distortions and blurring of the acquiredshort-exposure images. Corrections for these distortions have been tackled reasonably well by previousefforts, but still need improvement in the estimation of pixel shift maps to increase the restoration accuracy.This paper presents a new algorithm that efficiently estimates the shift maps from the geometricallydistorted video sequences and uses those maps to restore the sequences. A non-rigid image registrationmethod is employed to estimate the shift maps of the distorted frames against a reference frame. Thesharpest frame of the sequence, determined using a sharpness metric, is chosen as the reference frame.A k-means clustering technique is employed to discard too blurry frames that could result in inaccuracyin the shift maps’ estimation. The estimated pixel shift maps are processed to generate the accurate shiftmap that is used to dewarp the input frames into their non-distorted forms. The proposed method isapplied on several synthetic and real-world video sequences and the obtained results exhibit significantimprovements over the state-of-the-art methods.

A Vision-based Technique for Circle Detection and Measurement Using Look-up Table and Bitwise Center Accumulator

Hancheng Yu and Tuo Wang

Doc ID: 267297 Received 02 Jun 2016; Accepted 09 Dec 2016; Posted 12 Dec 2016  View: PDF

Abstract: In this paper, a fast algorithm for circle detection and measurement is proposed, which uses look-up table and bitwise center accumulator (LUT-BCA). The LUT-BCA is a two stage procedure. The first stage determines the candidate circle centers with normal lines produced by the look-up table and recorded by the bitwise center accumulator. The second stage computes the radius of each candidate circle centers and validates these centers, which eliminates the false detections. The proposed LUT-BCA can also be easily implemented on massively parallel high-performance graphics hardware using the Compute Unified Device Architecture (CUDA). Experimental results indicate that LUT-BCA can locate circle centers and measure their radii accurately and is very suitable for real-time circle detection and measurement.

Multi-focus image fusion via dictionary learning with rolling guidance filter

Xiang Yan, Hanlin Qin, and Jia Li

Doc ID: 274017 Received 18 Aug 2016; Accepted 04 Dec 2016; Posted 27 Jan 2017  View: PDF

Abstract: We present a new multi-focus image fusion method based on dictionary learning with rolling guidance filter to fusion of multi-focus images with registration and misregistration. First, we learn a dictionary via several classical multi-focus images blurred by rolling guidance filter. Subsequently, present a new model for focus regions identification via applying the learned dictionary to input images to obtain the corresponding focus feature maps. Then, determine the initial decision map via comparing the difference of the focus feature maps. The latter is to optimize the initial decision map and perform it on input images to obtain the fused images. Experimental results demonstrate that the suggested algorithm is competitive with the current state-of-the-art and superior to some representative methods when input images are well registered and misregistered.

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