Lidé

Ing. Jan Bednář, Ph.D.

Všechny publikace

Broadband Wollaston prism with a large output beam separation based on mercurous halides

  • DOI: 10.1364/OE.477544
  • Odkaz: https://doi.org/10.1364/OE.477544
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper proposes a Wollaston-type crystal polarizer suitable for broadband operation within the visible spectral band up to the far infrared band based on unique optical materials, mercurous halides (Hg2X2). This paper introduces the general characteristics and optical properties of these birefringent tetragonal optical materials, as well as the general description of a Wollaston prism and the process of its parameter optimization. In general, the Wollaston polarizer is constructed from two combined wedge-shaped prisms. The key parameters that affect the properties of the Wollaston polarizer are then the cut angle of these two prisms and the refractive index of the exploited optical cement (immersion) that bonds the prisms together. The optimal prism cut angles and immersion refractive index are investigated to maximize the Wollaston parameters, such as the transmittance of the polarized radiation and the separation angle of the output orthogonally polarized beams. This process is significantly dependent on the characteristics of all selected mercurous halides (Hg2Cl2, Hg2Br2, Hg2I2). The optimal values of the prism cut angle for each material are selected based on the outlined results. In addition, the Wollaston prism behaviour regarding real radiation propagation is modelled in detail via the Zemax optical studio. The presented models aim to aid in the real design and fabrication of a broadband Wollaston polarizer based on mercurous halides.

Quasi-collinear IR AOTF based on mercurous halide single crystals for spatio-spectral hyperspectral imaging

  • DOI: 10.1364/OE.420571
  • Odkaz: https://doi.org/10.1364/OE.420571
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper aims to show the advantages of the infrared-optimised quasi-collinear AOTF (acousto-optic tunable filter) for the spatio-spectral hyperspectral imaging system. The optimisation process is presented based on the selected tetragonal anisotropic materials with exceptional optical and acousto-optical properties in IR (infrared) spectral region. These materials are further compared in terms of their features and suitability for AOTF design. The spectral resolution is considered as the main optimising parameter. Resulting from the analysis, the mercurous chloride (Hg2Cl2) single crystal is selected as a representative of the mercurous halide family for the presentation of the quasi-collinear AOTF model operating in LWIR (long-wave infrared) spectral band. The overall parameters of the AOTF model such as spectral resolution, chromatic field of view, acoustic frequency, and operational power requirements are estimated and discussed in results.

Experimental setup for the quality evaluation of optical materials

  • DOI: 10.1109/RADIOELEK.2018.8376400
  • Odkaz: https://doi.org/10.1109/RADIOELEK.2018.8376400
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Modern photonic elements and systems are based upon novel optical materials. The material optical quality is a crucial parameter for any photonic application. The paper deals with the design and initial verification of optical quality evaluation system allowing fast near-mass-production evaluation of several qualitative parameters both spatially distributed and integral. The semi-automatic setup includes the schlieren-optics imaging, OFT (optical Fourier transform) imaging and integral metrics for overall quantitative assessment. Initial experimental results are demonstrated on mercurous chloride samples.

Toward astrometric calibration of ultrawide‐field images

  • DOI: 10.1002/asna.201813514
  • Odkaz: https://doi.org/10.1002/asna.201813514
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    In this paper, we introduce a new method of astrometric calibration tailored especially for ultrawide‐field systems like WILLIAM. The standard astrometric solution often fails to provide any result if the processed image contains a large amount of distortion, such as from a fisheye lens. Some algorithms yield the result, but the accuracy is satisfactory only at the center of the field of view. This work analyzes such images and proposes a new method that leads to much higher accuracy and success ratio of the calibration.

Pole searching algorithm for Wide-field all-sky image analyzing monitoring system

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Paper show how to find coordinates of the celestial pole. The algorithm is useful as the first hint for blind astrometry in order to help or speed up the process. The algorithm uses a principle of Hough transformation commonly used in computer vision.

PSF Estimation of Space-Variant Ultra-Wide Field of View Imaging Systems

  • DOI: 10.3390/app7020151
  • Odkaz: https://doi.org/10.3390/app7020151
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Ultra-wide-field of view (UWFOV) imaging systems are affected by various aberrations, most of which are highly angle-dependent. A description of UWFOV imaging systems, such as microscopy optics, security camera systems and other special space-variant imaging systems, is a difficult task that can be achieved by estimating the Point Spread Function (PSF) of the system. This paper proposes a novel method for modeling the space-variant PSF of an imaging system using the Zernike polynomials wavefront description. The PSF estimation algorithm is based on obtaining field-dependent expansion coefficients of the Zernike polynomials by fitting real image data of the analyzed imaging system using an iterative approach in an initial estimate of the fitting parameters to ensure convergence robustness. The method is promising as an alternative to the standard approach based on Shack-Hartmann interferometry, since the estimate of the aberration coefficients is processed directly in the image plane. This approach is tested on simulated and laboratory-acquired image data that generally show good agreement. The resulting data are compared with the results of other modeling methods. The proposed PSF estimation method provides around 5% accuracy of the optical system model.

Application of field dependent polynomial model

  • DOI: 10.1117/12.2237310
  • Odkaz: https://doi.org/10.1117/12.2237310
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Extremely wide-field imaging systems have many advantages regarding large display scenes whether for use in microscopy, all sky cameras, or in security technologies. The Large viewing angle is paid by the amount of aberrations, which are included with these imaging systems. Modeling wavefront aberrations using the Zernike polynomials is known a longer time and is widely used. Our method does not model system aberrations in a way of modeling wavefront, but directly modeling of aberration Point Spread Function of used imaging system. This is a very complicated task, and with conventional methods, it was difficult to achieve the desired accuracy. Our optimization techniques of searching coefficients space-variant Zernike polynomials can be described as a comprehensive model for ultra-wide-field imaging systems. The advantage of this model is that the model describes the whole space-variant system, unlike the majority models which are partly invariant systems. The issue that this model is the attempt to equalize the size of the modeled Point Spread Function, which is comparable to the pixel size. Issues associated with sampling, pixel size, pixel sensitivity profile must be taken into account in the design. The model was verified in a series of laboratory test patterns, test images of laboratory light sources and consequently on real images obtained by an extremely wide-field imaging system WILLIAM. Results of modeling of this system are listed in this article.

Měření vlastností extrémně širokoúhlých zobrazovacích systémů

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Měření parametrů extrémně širokoúhlých zobrazovacích systémů představuje problematickou úlohu, jak z hlediska korektního měřicího uspořádání, tak z hlediska vyhodnocení výsledků měření. Širokoúhlé objektivy používané v takových systémech, mezi které patří objektivy označované jako rybí oko, mají zorné pole až 180° u cirkulárních objektivů nebo 160° u diagonálních objektivů typu rybí oko. Objektivy s takto širokým zorným polem trpí několika optickými vadami, jako například distorzí, chromatickou aberací nebo nerovnoměrným osvětlením scény. Zvláštní pozornost je třeba věnovat obrazové kvalitě. V mnoha aplikacích, například u bezpečnostních kamer, astronomických kamer a dalších, je požadovaná uniformita obrazu v celém zorném poli, protože celé zorné pole může obsahovat důležité detaily. Stejně jako u méně extrémních objektivů je jedním z hledisek jak posuzovat kvalitu zobrazení měření MTF (Modulation Transfer Function) a rozlišovací schopnosti. Měření těchto charakteristik u širokoúhlých objektivů přináší nové výzvy a je nutné přizpůsobit měřicí metody distorzním vlastnostem objektivu. Tento článek se zabývá právě korekcí měření MTF, rozlišovací schopnosti a chromatické aberace, tak aby výsledky reflektovaly netypické zobrazení scény.

OFT Sectorization Approach to Analysis of Optical Scattering in Mercurous Chloride Single Crystals

  • DOI: 10.1364/OE.23.021509
  • Odkaz: https://doi.org/10.1364/OE.23.021509
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper is devoted to the application of the optical Fourier transform (OFT) to the study and evaluation of optical scattering in the latest generation of calomel single crystals ready for application in several possible devices such as IR polarizers and acoustooptic tunable filters (AOTF). There are numerous effects that are responsible for the scattering of an optical wave passing through the crystal sample volume and surface layers, and they affect the optical crystal quality. The scattering level is a crucial and limiting parameter in many technical applications of an evaluated crystal. The proposed approach is based upon the high dynamic range optical FT configuration, creating the amplitude spectrum in the focal plane and its spatial angular distribution analysis based on the spectrum sectorization. The optical scattering pattern was tested in nine locations within each crystal sample volume and on numerous crystal samples. The experimental results are presented and discussed.

Optická Fourierova transformace

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    V současné době se v různých oblastech zpracování signálů setkáváme s využitím Fourierovy transformace nejen při zpracování jednorozměrných signálů, ale také vícerozměrných signálů, např. obrazů. Ať již popisujeme transformaci prováděnou se signály některou z metod Fourierovy transformace - diskrétní Fourierovou transformací (DFT), krátkodobou Fourierovou transformací (STFT), vždy při digitálním zpracování dojdeme k použití algoritmu rychlé Fourierovy transformace (FFT). Pro zpracování obrazu se nabízí i jiná alternativa, přímé využití optiky, kdy Fourierovu transformaci obrazu provádí samotný optický systém. Jednoduše se tak dá realizovat filtrace např. horní nebo dolní propustí (HP - high pass, resp. LP - low pass). V následujícím textu bude předvedeno jedno z možných odvození optické Fourierovy transformace (OFT), bude představen princip činnosti systému realizujícího OFT a budou ukázány příklady typických obrazových předloh, jejich spekter a podoby po prostorové filtraci..

Performance evaluation of image deconvolution techniques in space-variant astronomical imaging systems with nonlinearities

  • DOI: 10.1117/12.2187888
  • Odkaz: https://doi.org/10.1117/12.2187888
  • Pracoviště: Katedra kybernetiky, Katedra radioelektroniky
  • Anotace:
    There are various deconvolution methods for suppression of blur in images. In this paper a survey of image deconvolution techniques is presented with focus on methods designed to handle images acquired with wide-field astronomical imaging systems. Image blur present in such images is space-variant especially due to space-variant point spread function (PSF) of the lens. The imaging system can contain also nonlinear electro-optical elements. Analysis of nonlinear and space-variant imaging systems is usually simplified so that the system is considered as linear and space-invariant (LSI) under specific constraints. Performance analysis of selected image deconvolution methods is presented in this paper, while considering space-variant nature of wide-field astronomical imaging system. Impact of nonlinearity on the overall performance of image deconvolution technique is also analyzed. Test images with characteristics obtained from the real system with space-variant wide-field input lens and nonlinear image intensifier are used for the performance analysis.

Stellar objects identification using wide-field camera

  • Autoři: Janout, P., prof. Mgr. Petr Páta, Ph.D., Ing. Jan Bednář, Ph.D., Anisimova, E., Blažek, M., Skala, P.
  • Publikace: Proc. SPIE 9450, Photonics, Devices, and Systems VI. Bellingham: SPIE, 2015. p. 94501I-1-94501I-9. Proceedings of SPIE. ISSN 0277-786X. ISBN 978-1-62841-566-7.
  • Rok: 2015
  • DOI: 10.1117/12.2074255
  • Odkaz: https://doi.org/10.1117/12.2074255
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper deals with evaluation and processing of astronomical image data, which are obtained by a wide- field all-sky image analyzing monitoring system (WILLIAM). The WILLIAM is an additional experimental camera for project MAIA equipped with wide-field lens. The system can detect stellar objects as faint as 6th magnitude. Acquired image data are processed by an algorithm for stellar object detection and identification which is based on coordinates transfer function. Cartesian coordinates at the image data are transformed to horizontal coordinate system. This coordinate system allows searching in astronomical catalogues of stellar objects. This paper presents the components of WILLIAM, its measured electro-optical characteristics and some results of identification.

Estimation and measurement of space-variant features of imaging systems and influence of this knowledge on accuracy of astronomical measurement

  • DOI: 10.1117/12.2061736
  • Odkaz: https://doi.org/10.1117/12.2061736
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Additional monitoring equipment is commonly used in astronomical imaging. This electro-optical system usually complements the main telescope during acquisition of astronomical phenomena or supports its operation e.g. evaluating the weather conditions. Typically it is a wide-field imaging system, which consists of a digital camera equipped with fish-eye lens. The wide-field imaging system cannot be considered as a space-invariant because of space-variant nature of its input lens. In our previous research efforts we have focused on measurement and analysis of images obtained from the subsidiary all-sky monitor WILLIAM (WIde-field aLL-sky Images Analyzing Monitoring system). Space-variant part of this imaging system consists of input lens with 180 fi angle of view in horizontal and 154 fi in vertical direction. For a precise astronomical measurement over the entire field of view, it is very important to know how the optical aberrations affect characteristics of the imaging system, especially its PSF (Point Spread Function). Two methods were used for characterization of the space-variant PSF, i.e. measurement in the optical laboratory and estimation using acquired images and Zernike polynomials. Analysis of results obtained using these two methods is presented in the paper. Accuracy of astronomical measurements is also discussed while considering the space-variant PSF of the system.

Analysis of images obtained from space-variant astronomical imaging systems

  • DOI: 10.1117/12.2023904
  • Odkaz: https://doi.org/10.1117/12.2023904
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Most of the classical approaches to the measurement and modeling of electro-optical imaging systems rely on the principles of linearity and space invariance (LSI). In our previous research efforts we have focused on measurement and analysis of images obtained from a double station video observation system MAIA (Meteor Automatic Imager and Analyzer). The video acquisition module of this system contains wide-field input lens which contributes to space-variability of the imaging system. For a precise astronomical measurement over the entire field of view, it is very important to comprehend how the characteristics of the imaging system can affect astrometric and photometric outputs. This paper presents an analysis of how the space-variance of the imaging system can affect precision of astrometric and photometric results. This analysis is based on image data acquired in laboratory experiments and astronomical observations with the wide-field system. Methods for efficient calibration of this system to obtain precise astrometric and photometric measurements are also proposed.

Astronomical Image Denoising using Curvelet and Starlet Transform

  • DOI: 10.1109/RadioElek.2013.6530927
  • Odkaz: https://doi.org/10.1109/RadioElek.2013.6530927
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    Astronomical image data acquisition under low light conditions causes higher noise occurrence in these data. There are a lot of noise sources including also the thermally generated noise (dark current) inside used astronomical CCD sensor and the Poisson noise of the photon flux. There are specific image quality criteria in astronomy. These criteria are derived from the algorithms for astronomical image processing and are specific in the field of multimedia signal processing. Astrometric and photometric algorithms provide information about stellar objects: their brightness profile (PSF), position and magnitude. They could fail because of lower SNR. This problem can be solved by subtraction a dark frame from a captured image nowadays. However, this method couldn't work properly in systems with shorter shutter speed and nonlinear sensitivity, such as for example the system MAIA (Meteor Automatic Imager and Analyser). Image data from these system could not been processed by conventional algorithms. Denoising of the astronomical images is therefore still a big challenge for astronomers and people who process astronomical data. Therefore new algorithms are proposed in this paper. We describe our experiences with astronomical image data denoising based on Curvelet and Starlet transform. Novel algorithms have been tested on image data from MAIA system. Their influence on the stellar object detecting algorithms and on important photometric data like stellar magnitude and FWHM (Full Width at Half Maximum) has been studied and compared with conventional denoising methods.

Efficiency of Wavelet Coefficients Thresholding Techniques used for Multimedia and Astronomical Image Denoising

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper deals with image denoising based on the wavelet transform realized by Mallat algorithm and À trous algorithm. The effectiveness of global and subband thresholding techniques are studied on multimedia and astronomical images contaminated by Gaussian noise. Experimental results on several testing images are compared with each other from two objective quality aspects (PSNR, RMSE). Astronomical image denoising techniques differ from those used for multimedia images, because astronomical data are processed by computers and are not evaluated by humans. Thus we show especially the difference between quality criteria related with both types of images after denoising. In case of astronomical data, important scientific criteria as stellar magnitude and FWHM (Full Width at Half Maximum) changes are studied in processed images after noise removal.

The Point Spread Function Variations inside Wide-field Astonomical Images

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The Point Spread Function (PSF) of the astronomical imaging system is usually approximated by a Gaussian or Moffat function. For simplification, the astronomical imaging system is considered to be time and space invariant. This means that invariable PSF within an exposed image is assumed. If real wide-field imaging systems are considered, this presumption is not fulfilled. In real systems, stronger optical aberrations are expected (especially coma) at greater distances from the center of the captured image. This impacts the efficiency of stellar astrometry and photometry algorithms, so it is necessary to know the PSF variation. In this paper, we perform the first step toward assigning PSF changes: we study the dependence of the Moffat function fitting parameters (FWHM and the atmospheric scattering coefficient) on the position of a stellar object.

Zpracování obrazu pomocí vlnkové transformace

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    V tomto článku autoři shrnuli vlastnosti vlnkové transformace tak, aby z nich vyplývaly důvody k použití tohoto užitečného nástroje za účelem analýzy a zpracování jak jednorozměrných, tak i dvourozměrných signálů, a to počínaje odstraněním šumu, přes kódování a doostření signálů až po detekci objektů. Autoři se snažili pojmout výklad co nejvíce pochopitelnou formou, zahrnující co největší počet slovního vysvětlení a přehledných obrázků.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk