DOCSLIB.ORG

3D-Visualization of Caustics' Formation in Laser Refractography

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
3D-Visualization of Caustics' Formation in Laser Refractography Available online at www.sciencedirect.com ScienceDirect Physics Procedia 73 ( 2015 ) 205 – 210 4th International Conference Photonics and Infoformation Optics, PhIO 2015, 28-30 January 2015 3D-visualization of caustics’ formation in laser refractography problems A.V. Vedyashkina*, B.S. Rinkevichyus Nattional Research University “Moscow Power Engineering Institute”, V.A. Fabricant Physics Department, Krasnokazarmennaya st. 14, Moscow 111250, Russia Abstract In an optically homoogeneous medium (a medium in which the refractive index is the same in any point) light spreads rectilinearly without being refracted. However, the refractive index can be changed, its gradient can be created as a result of making inhomogeneity. Such inhomogeneity can be made by diffusion of liquids or their heating, cooling, and so on. One actual and promising method of researching optically inhomogeneous media is the method of the laser refractography. It is based on the phenomenon of refraction of structured laser radiation in optically inhomogeneous media and registration of its form deviations with the digital camera. Two types of optical inhomogeneitiees are researched in this work: a diffusion llayer of liquids and temperature fields near heated or cooled objects. It was considered conditions for the occurrence of caustics in longitudinal probing of optical sttratified inhomogeneous media by plane and cylindrical laser beams in this paper. Experimental setup for 3D- visualization of laser beams’ refraction was shown. © 20152015 The The Authors. Author s.Published Published by bElseviery Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of the National). Research Nuclear University MEPhI (Moscow Engineering PPhysics Institute). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Keywords: caustics; structured laser radiation; laser refractography; refraction’s dynamics; 3D-visualization; optical inhomogeneous medium; diffusive layer. 1. Introduction Currently research of optically inhomogeneous media represents great scientific interest. IIn such media the refractive index is not the same in any point and light spreads due to refraction not rectilinearly. Itt is often important to know what occurs when two or more mediums with diffferent physical characteristics contact eaach other, how the * Corresponding author. Tel.: +79152265230. E-mail address: [email protected] 1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) doi: 10.1016/j.phpro.2015.09.158 206 A.V. Vedyashkina and B.S. Rinkevichyus / Physics Procedia 73 ( 2015 ) 205 – 210 refractive index of liquid changes by heating or cooling objects inside it. Methods for optically inhomogeneity exploration can be significant in researches of the diffusion process, optimization of heating or cooling elements’ work. One method of investigation optically inhomogeneous media is the method of laser refractography. It is based on the phenomenon of refraction of structured laser radiation (SLR) in optically inhomogeneous media and registration of its form deviations with the digital camera [Rinkevichyus, Evtikhieva, Raskovskaya (2011), Raskovskaya, Rinkevichyus, Tolkachev (2011)]. This method is in essence different from the previously known methods for researching of optically inhomogeneity such as schlieren and shadowgraph techniques [Settles (2001)]. Application of laser techniques for the reconstruction of physical characteristics of medium, causing inhomogeneity of the refractive index it is advisable to probe medium by structured laser beams (SLB) formed by diffractive optical elements (DOE). Use of structured laser radiation as opposed to wide light beams allows with high accuracy to estimate changes of the refractive index in the boundary layer. Bright light fanciful curves arise on the lit table, on which a glass of water was put. Similar moving curves can be seen at the bottom of a shallow pond, water surface of which is roughness. This curves are caustics. Caustic is the envelope of light rays reflected or refracted by the curved surface or object [Born, Wolf (1999)]. But in this method, caustics are special lines and special surfaces near which the intensity of the light field increases sharply [Vedyashkina (2013)]. Other optical methods of caustics are widely used in various problems such as [Pazis, Agioutantis, Kourkoulis (2011), Gao, Li, Negehban (2014)]. When probing inhomogeneity by SLB caustics appears, its location can be determined using refractogram processing program with high precision, it is possible to solve the inverse task of finding properties of the inhomogeneous medium. Theory of caustics is directly related with one of mathematical section – the theory of catastrophes [Arnold, Gusein-Zade, Varchenko (2012)]. Computer and experimental 3D-visualization in laser refractography technique helps better understand the structure of inhomogeneity in liquids. 2. Description of the method of shots modelling Diffusive layer of liquid is a special type of inhomogeneity, which appears near interface of two liquid media with various physical characteristics. In this work liquids with various refraction indexes are considered. The diffusion layer is a stratified medium, the refractive index depends only on the one Cartesian coordinate. Thus, when slowly pouring thin layer of less dense liquid with the refractive index n1 on the surface of optically denser liquid with the refractive index n2 eventually between them the diffusion layer is formed, its refractive index can be described by the following expression of hyperbolic tangent [Raskovskaya (2014)]: nn12 nn 12§· xx s nx() th¨¸, (1) 22©¹h where h – characteristic half-width of layer, xs – middle of layer. Layer’s boundaries x1 and x2 are determined by the -5 level of deviation from the refractive index values n1 and n2 at 10 respectively. This type of optical inhomogeneity can be probed by SLR of various forms: line, matrix of dots, set of conical rings, cross lines and etc. Computer and experimental 3D-visualization of the plane laser beam refraction and dynamics of the caustics’ formation when changing laser plane’s elevation angle and the refractive index gradient are described in [Vedyashkina, Pavlov, Raskovskaya, Rinkevichyus (2014)]. Relation (2) is the equation of the ray trajectory in a plane-layered medium, given the refractive index distribution n(x) and the initial conditions z0 = z(0), Į0 – the angle under which the ray enters the medium, n0 – refraction index in entry point of the ray in medium: A.V. Vedyashkina and B.S. Rinkevichyus / Physics Procedia 73 ( 2015 ) 205 – 210 207 x n0 sinĮ0dx zx() z . (2) 0 ³ 2 22 0 r nx( ) n0 sin Į0 Using this exprression it is possible to simulate propagation of a parallel cylindrical laser beam in diffusion layer of liquid. Let layered-inhomogeneous medium in which there is the diffusive layer has the following parameters: n1 = 1.3380, n2 = 1.3320, xs = 50 mm, h = 1.1 mm. For visualization of caustics there are three characteristic main positions: laser beam’s center lies in the planes of the upper, lower booundaries layer and in the plane of middle of layer. Fig. 1 shows this causes, different colors show the different radii of the cylinders (red – 8 mm, green – 16 mm). a b c Fig. 1. Modeling of 3D-visualization of cylindrical laser beam’s refraction in diffusive layer of liquid and caustics (1) formation: (a)) beam’s center lies in the plane of middle of layer; (b) beam’s center lies in the plane of upper bounddaary; (c) beam’s center lies in the plane of lower boundary In order to observe and register refractogram of cylinddrrical laser beam propagation in inhomogeneous media it is possible to use experimental setup, which is presented in Fig. 2. To form cylindrical laser beeam it was created optical system, which consists of laser 1, lens 2 for focusinng beam in registration area, DOE 3 and lens 4 for making beam parallel. In order to receive 3D-refractograms without distortion it was suggested to use two cuvettes [Yesin, Raskovskaya, Rinkevichyus, Tolkachev (2012)]. Creation of diffusive layer is taking place in cuvette 5, registration of refractogram is implementeed in the second cuvette 6. Registration of 3D-refractoram 8 was made by digital camera 7 and processed on personal computer 9. For creation of diffusive layer of liquid we used distilled water and watere -NaCl mixture. Refractogram storing was made by recording the scattered radiation on special particles added in water. Parameters of medium: refractive indexes of salinne water n1 = 1.3410 and distilled water n2 = 1.3320. Fig. 2. Experimental setup: 1 – laser, 2, 4 – lenses, 3 – DOE, 5 – cuvette with diffusive layer of liquid, 6 – cuvette with sscattering particles in water, 7 – digital camera, 8 – 3D-refractogram, 9 – PC 208 A.V. Vedyashkina and B.S. Rinkevichyus / Physics Procedia 73 ( 2015 ) 205 – 210 3D-refractogram of the laser beam propagating in the inhomogeneous medium is shown in Figg. 3. 1 a b 1 1 c d Fig. 3. Experimental 3D-refractogram of cylindrical laser beam’s refraction in diffusive layer of liquid and caustics (1) foormation: (a) laser beam propagation in homogeneous medium; (b) beam’s center lies in the plane of middle of layer; (c) beam’s center lies in the plane upper boundary; (d) beam’s center lies in the plane lower boundary 3. Spherically inhomogeneous mediums Distribution of refraction index in spherically symmetric temperature field near cold ball withh the radius R in hot water can by described by the radial temperature dependence: 2 rR (3) a2 Tr TT0 'e, where T 0, 'T, a – are the parameters of the temperature field model, the T 0 parameter is determine by temperature of cuvette’s wallls with liquid, and the relation of 'T/a corresponds to the gradient of the temperature field in A.V.
Load more

Recommended publications
  • Classical and Modern Diffraction Theory
    Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3701993/frontmatter.pdf by guest on 29 September 2021 Classical and Modern Diffraction Theory Edited by Kamill Klem-Musatov Henning C. Hoeber Tijmen Jan Moser Michael A. Pelissier SEG Geophysics Reprint Series No. 29 Sergey Fomel, managing editor Evgeny Landa, volume editor Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3701993/frontmatter.pdf by guest on 29 September 2021 Society of Exploration Geophysicists 8801 S. Yale, Ste. 500 Tulsa, OK 74137-3575 U.S.A. # 2016 by Society of Exploration Geophysicists All rights reserved. This book or parts hereof may not be reproduced in any form without permission in writing from the publisher. Published 2016 Printed in the United States of America ISBN 978-1-931830-00-6 (Series) ISBN 978-1-56080-322-5 (Volume) Library of Congress Control Number: 2015951229 Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3701993/frontmatter.pdf by guest on 29 September 2021 Dedication We dedicate this volume to the memory Dr. Kamill Klem-Musatov. In reading this volume, you will find that the history of diffraction We worked with Kamill over a period of several years to compile theory was filled with many controversies and feuds as new theories this volume. This volume was virtually ready for publication when came to displace or revise previous ones. Kamill Klem-Musatov’s Kamill passed away. He is greatly missed. new theory also met opposition; he paid a great personal price in Kamill’s role in Classical and Modern Diffraction Theory goes putting forth his theory for the seismic diffraction forward problem.
    [Show full text]
  • Image-Space Caustics and Curvatures
    Image-space Caustics and Curvatures Xuan Yu Feng Li Jingyi Yu Department of Computer and Information Sciences University of Delaware Newark, DE 19716, USA fxuan,feng,[email protected] Abstract Caustics are important visual phenomena, as well as challenging global illumination effects in computer graph- ics. Physically caustics can be interpreted from one of two perspectives: in terms of photons gathered on scene geom- etry, or in terms of a pair of caustic surfaces. These caustic surfaces are swept by the foci of light rays. In this paper, we develop a novel algorithm to approximate caustic sur- faces of sampled rays. Our approach locally parameterizes rays by their intersections with a pair of parallel planes. We show neighboring ray triplets are constrained to pass simul- taneously through two slits, which rule the caustic surfaces. We derive a ray characteristic equation to compute the two slits, and hence, the caustic surfaces. Using the characteris- tic equation, we develop a GPU-based algorithm to render the caustics. Our approach produces sharp and clear caus- tics using much fewer ray samples than the photon mapping method and it also maintains high spatial and temporal co- herency. Finally, we present a normal-ray surface repre- Figure 1. We use our caustic-surface-based sentation that locally parameterizes the normals about a algorithm to render the refraction caustics surface point as rays. Computing the normal ray caustic cast by a crystal bunny of 69473 triangles. On surfaces leads to a novel real-time discrete shape operator. an NVidia GeForce7800, our method renders at 115 fps at an image resolution of 512x512.
    [Show full text]
  • Caustic Architecture Article
    Tricks'of'the'light' An#extended#version#of#an#article#in#New$Scientist,#30#January#2013# # Two#men#enter#the#darkened#stage,#apparently#carrying#a#thick#slab#of#badly# made#glass,#like#the#stuff#in#the#windows#of#old#houses#that#turns#the#world# outside#wobbly.#They#hold#it#up,#and#computer#scientist#Mark#Pauly#shines#a# torch#at#it.#The#crowd#in#this#Parisian#auditorium#gasps#and#then#breaks#into# spontaneous#applause.# For#there#on#the#screen#behind,#conjured#out#of#this#piece#of#nearFfeatureless# material#–#not#glass,#in#fact,#but#transparent#acrylic#plastic#(Perspex)#–#is#a# projected#image#of#Alan#Turing,#the#computer#pioneer#whose#centenary#is# celebrated#this#year.#Every#thread#of#his#thick#tweed#jacket#is#picked#out#in#light# and#shadow.#But#where#is#the#image#coming#from?#It#can#only#be#the#transparent# slab,#but#there#seems#to#be#nothing#there#to#produce#it,#nothing#but#a#slightly# uneven#surface.# # An#image#of#Alan#Turing#conjured#from#light#passing#through#a#slab#of#Perspex#at#the# Advances#in#Architectural#Geometry#conference#in#Paris,#September#2012.# This#image#is#made#from#rays#refracted,#folded#and#focused#by#the#slightly# uneven#surface#of#the#acrylic#block.#It’s#similar#to#the#filigree#of#bright#bands#seen# on#the#bottom#of#a#swimming#pool#in#the#sunlight,#called#a#caustic#and#caused#by# the#way#the#wavy#surface#refracts#and#focuses#light.#Caustics#are#familiar#enough,# but#they#never#looked#like#this#before.#Those#made#by#sunlight#shining#through# an#empty#glass#are#a#random#mass#of#cusps#and#squiggles.#Pauly,#a#specialist#in#
    [Show full text]
  • Real-Time Caustics
    EUROGRAPHICS 2003 / P. Brunet and D. Fellner Volume 22 (2003), Number 3 (Guest Editors) Real-Time Caustics M. Wand and W. Straßer WSI/GRIS, University of Tübingen Abstract We present a new algorithm to render caustics. The algorithm discretizes the specular surfaces into sample points. Each of the sample points is treated as a pinhole camera that projects an image of the incoming light onto the diffuse receiver surfaces. Anti-aliasing is performed by considering the local surface curvature at the sample points to filter the projected images. The algorithm can be implemented using programmable texture mapping hardware. It allows to render caustics in fully dynamic scenes in real-time on current PC hardware. Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture / Image Generation – Display Algo- rithms; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism 1. Introduction tion step has to be performed that is often even more ex- pensive. Thus, the technique is usually not very efficient. A real-time simulation of the interaction of light with Although the implementation techniques for raytracing complex, dynamically changing scenery is still one of the queries have made impressive advances in the last few major challenges in computer graphics. In this paper, we years29, raytracing based algorithms still need a consider- look at a special global illumination problem, rendering of able amount of computational power (such as a cluster of caustics. Caustics occur if light is reflected (or refracted) at several high end CPUs) to calculate global illumination one or more specular surfaces, focused into ray bundles of solutions in real time30.
    [Show full text]
  • Adaptive Spectral Mapping for Real-Time Dispersive Refraction By
    Adaptive Spectral Mapping for Real-Time Dispersive Refraction by Damon Blanchette A Thesis Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Master of Science in Computer Science by ___________________________________ January 2012 APPROVED: ___________________________________ Professor Emmanuel Agu, Thesis Adviser ___________________________________ Professor Matthew Ward, Thesis Reader ___________________________________ Professor Craig Wills, Head of Department Abstract Spectral rendering, or the synthesis of images by taking into account the wavelengths of light, allows effects otherwise impossible with other methods. One of these effects is dispersion, the phenomenon that creates a rainbow when white light shines through a prism. Spectral rendering has previously remained in the realm of off-line rendering (with a few exceptions) due to the extensive computation required to keep track of individual light wavelengths. Caustics, the focusing and de-focusing of light through a refractive medium, can be interpreted as a special case of dispersion where all the wavelengths travel together. This thesis extends Adaptive Caustic Mapping, a previously proposed caustics mapping algorithm, to handle spectral dispersion. Because ACM can display caustics in real-time, it is quite amenable to be extended to handle the more general case of dispersion. A method is presented that runs in screen-space and is fast enough to display plausible dispersion phenomena in real-time at interactive frame rates. i Acknowledgments I would like to thank my adviser, Professor Emmanuel Agu, for his guidance, laughs, and answering my hundreds of questions over the year it took to complete this thesis. The beautiful video card helped, too.
    [Show full text]
  • Advanced Computer Graphics CS 563: Adaptive Caustic Maps Using Deferred Shading
    Advanced Computer Graphics CS 563: Adaptive Caustic Maps Using Deferred Shading Frederik Clinckemaillie Computer Science Dept. Worcester Polytechnic Institute (WPI) ItIntrod ucti on: CtiCaustics Reflective Caustics Refractive Caustics IdiIntroduction: CiCaustic MiMapping Much faster than path tracing algorithms Two‐pass process Similar to photon mapping Creates a caustic intensity map CtiCaustic MiMapping Three Step Process 1) Photon Emission 2) Rearrangement into Caustic Map 3) Caustic Map Projection CtiCaustic MiMapping Phot on EiiEmission Rasterizes from light view to generate grid of photons Creates photon buffer 2D image storing final photon hit points In conjunction with shadow maps Allows quick lookups to determine Indirect lighting from caustics CtiCaustic Map CtiCreation Controls lighting quality and cost Splatting photons into caustic map becomes bo ttlenec k Crisp noise‐free images require millions of phthotons Not feasible in interactive time Hierarchical caustic maps: discard unimportant parts of photon buffer to improve speed Uses multi‐resolution caustic map to reduce splatting costs Problems Poor photon sampling due to rasterization leads to under and over sampling Proper sampling resolution cannot be determined Millions of photons are required for high‐quality caustics. Processing each is too expensive Photon sampling location can change between frames, leading to coherency problems Photon sampling is not dynamic DfDeferre d Shadi ng Good sampling rates cannot be computed Ideally, number of photons is determined adtildaptively Hierarchical Caustic Map(HCM) Has a maximum number of photons, not all are processed Pho ton EiiEmission and CtiCaustic Map GtiGeneration should be coupled DfDeferre d Shadi ng Postpones final illumination computations until visible fragments are identified HCMs generates grid of phthotons and only processes relevant ones DfDeferre d Sha ding never generates ilirrelevan t photons.
    [Show full text]
  • Controlling Caustics
    Controlling Caustics Mark Pauly1, Michael Eigensatz, Philippe Bompas, Florian Rist2, Raimund Krenmuller2 1 EPFL 2 TU Wien Keywords 1 = Caustic 2 = Refraction 3 = Refl ection 4 = Design 5 = Milling 6 = Slumping Abstract Caustics are captivating light patterns created by materials focusing or diverting Figure 1 Left: A typical caustic created by a curved glass object appears chaotic and random. Right: Our light by refraction or refl ection. We know method creates glass objects that cast controlled caustics by optimization of the glass surface geometry alone. caustics as random side effects, appearing, The portrait of Alan Turing emerges from a beam of uniform light that is refracted by the circular glass piece. for example, at the bottom of a swimming pool, or generated by many glass objects, like drinking glasses or bottles. In this paper we show that it is possible to control caustic patterns to form almost any desired shape by optimizing the geometry of the refl ective or refractive surface generating the caustic. A seemingly fl at glass window, for example, can produce the image of a person as a caustic pattern on the fl oor, generated solely by the sunlight entering through that window. We demonstrate how this surprising result offers a new perspective on light control and the use of caustics as an inspiring design element in architecture, product design and beyond. Several produced samples illustrate that physical realizations of such optimized geometry are feasible. 1 Introduction The interaction of light with glass plays an important role for the perception and functionality of many glass products. One of the most fascinating light phenomena with glass objects are caustics: light gets focused and diverted when passing through the glass, creating an intriguing pattern of varying light intensity.
    [Show full text]
  • Geometric Optics 1 7.1 Overview
    Contents III OPTICS ii 7 Geometric Optics 1 7.1 Overview...................................... 1 7.2 Waves in a Homogeneous Medium . 2 7.2.1 Monochromatic, Plane Waves; Dispersion Relation . ........ 2 7.2.2 WavePackets ............................... 4 7.3 Waves in an Inhomogeneous, Time-Varying Medium: The Eikonal Approxi- mationandGeometricOptics . .. .. .. 7 7.3.1 Geometric Optics for a Prototypical Wave Equation . ....... 8 7.3.2 Connection of Geometric Optics to Quantum Theory . ..... 11 7.3.3 GeometricOpticsforaGeneralWave . .. 15 7.3.4 Examples of Geometric-Optics Wave Propagation . ...... 17 7.3.5 Relation to Wave Packets; Breakdown of the Eikonal Approximation andGeometricOptics .......................... 19 7.3.6 Fermat’sPrinciple ............................ 19 7.4 ParaxialOptics .................................. 23 7.4.1 Axisymmetric, Paraxial Systems; Lenses, Mirrors, Telescope, Micro- scopeandOpticalCavity. 25 7.4.2 Converging Magnetic Lens for Charged Particle Beam . ....... 29 7.5 Catastrophe Optics — Multiple Images; Formation of Caustics and their Prop- erties........................................ 31 7.6 T2 Gravitational Lenses; Their Multiple Images and Caustics . ...... 39 7.6.1 T2 Refractive-Index Model of Gravitational Lensing . 39 7.6.2 T2 LensingbyaPointMass . .. .. 40 7.6.3 T2 LensingofaQuasarbyaGalaxy . 42 7.7 Polarization .................................... 46 7.7.1 Polarization Vector and its Geometric-Optics PropagationLaw. 47 7.7.2 T2 GeometricPhase .......................... 48 i Part III OPTICS ii Optics Version 1207.1.K.pdf, 28 October 2012 Prior to the twentieth century’s quantum mechanics and opening of the electromagnetic spectrum observationally, the study of optics was concerned solely with visible light. Reflection and refraction of light were first described by the Greeks and further studied by medieval scholastics such as Roger Bacon (thirteenth century), who explained the rain- bow and used refraction in the design of crude magnifying lenses and spectacles.
    [Show full text]
  • Rendering Techniques for Transparent Objects
    173 Rendering Techniques for Transparent Objects Mikio Shinya* Takafumi Saito Tokiichiro Takahashi NTT Human Interface Laboratories 1-2356, Take, Yokosuka-shi, Kanagawa, Japan Abstract situations, however, simple application of ray tracing is not Three techniques are proposed for more realistic adequate to render photo-realistic images of transparent objects, because other important phenomena occur due to image synthesis of transparent objects. The tech­ refraction and/or reflection. For example: niques simulate important phenomena due to refrac­ tion and/or reflection, such as focuses and disper­ • caustics and focuses; Refraction and reflection sion. For efficient simulation of focuses and caus­ causes light concentration, resulting in a complex pat­ tics, a method called grid-pencil tracing is proposed, tern of caustics and fo cuses. This phenomenon is of­ based on the ideas of pencil tracing and backward ten observed in water scenes (swimming pools, sea­ ray tracing. An anti-aliasing filter is designed for side, and so on) and can even be produced by a glass grid-pencil tracing in area-source illumination envi­ of water. ronments. The theory of pencil tracing is also ap­ • dispersion; Due to dispersion, a rainbow spectrum plied to dispersion simulation. An extension of the is often produced by transparent objects, such as prisms, theory provides a basis for dispersi ve pencil tracing, gemstones, and cut-glass. where both spatial coherency and 'wavelength co­ herency' is effectively used for fast image synthesis • extremely bright spots; Reflection of primary of dispersive objects. light sources are manifested as extremely bright spots. Furthermore, a linear filtering technique is ap­ The glint off a knife or shimmering light reflected off plied to effectively express extremely bright spots a body of water, for example.
    [Show full text]
  • Efficient Freeform Lens Optimization for Computational Caustic Displays
    Efficient freeform lens optimization for computational caustic displays Gerwin Damberg1;3 and Wolfgang Heidrich2;1;4 1Department of Computer Science, University of British Columbia 2Visual Computing Center, King Abdullah University of Science and Technology [email protected] [email protected] www.cs.ubc.ca/ gdamberg/ Abstract: Phase-only light modulation shows great promise for many imaging applications, including future projection displays. While images can be formed efficiently by avoiding per-pixel attenuation of light most projection efforts utilizing phase-only modulators are based on holographic principles utilizing interference of coherent laser light and a Fourier lens. Limitations of this type of an approach include scaling to higher power as well as visible artifacts such as speckle and image noise. We propose an alternative approach: operating the spatial phase modulator with broadband illumination by treating it as a programmable freeform lens. We describe a simple optimization approach for generating phase modulation patterns or freeform lenses that, when illuminated by a colli- mated, broadband light source, will project a pre-defined caustic image on a designated image plane. The optimization procedure is based on a simple geometric optics image formation model and can be implemented compu- tationally efficient. We perform simulations and show early experimental results that suggest that the implementation on a phase-only modulator can create structured light fields suitable, for example, for efficient illumination of a spatial light modulator (SLM) within a traditional projector. In an alternative application, the algorithm provides a fast way to compute geometries for static, freeform lens manufacturing. © 2015 Optical Society of America OCIS codes: (080.4225) Nonspherical lens design; (120.2040) Displays; (100.3190) Inverse problems; (110.1758) Computational imaging.
    [Show full text]
  • Caustics Mapping: an Image-Space Technique for Real-Time Caustics Musawir Shah, Sumanta Pattanaik
    SCHOOL OF ENGINEERING AND COMPUTER SCIENCE, UNIVERSITY OF CENTRAL FLORIDA, CS TR 50-07 1 Caustics Mapping: An Image-space Technique for Real-time Caustics Musawir Shah, Sumanta Pattanaik Abstract— In this paper, we present a simple and prac- tical technique for real-time rendering of caustics from reflective and refractive objects. Our algorithm, concep- tually similar to shadow mapping, consists of two main parts: creation of a caustic map texture, and utilization of the map to render caustics onto non-shiny surfaces. Our approach avoids performing any expensive geometric tests, such as ray-object intersection, and involves no pre-computation; both of which are common features in previous work. The algorithm is well suited for the standard rasterization pipeline and runs entirely on the graphics hardware. I. INTRODUCTION AUSTICS are complex patterns of shimmering C light that can be seen on surfaces in presence of reflective or refractive objects, for example those formed on the floor of a swimming pool in sunlight. Caustics occur when light rays from a source, such as the sun, get refracted, or reflected, and converge at a single point on a non-shiny surface. This creates the non-uniform dis- Fig. 1. Image rendered using the caustics mapping algorithm. This result was obtained using double surface refraction (both for the tribution of bright and dark areas. Caustics are a highly appearance of the bunny as well as for the caustics) at the rate of desirable physical phenomenon in computer graphics due 31 fps. to their immersive visual appeal. Some very attractive results have been produced using off-line high quality rendering systems; however, real-time caustics remain open to more practical solutions.
    [Show full text]
  • Reparameterizing Discontinuous Integrands for Differentiable Rendering Guillaume Loubet, Nicolas Holzschuch, Wenzel Jakob
    Reparameterizing Discontinuous Integrands for Differentiable Rendering Guillaume Loubet, Nicolas Holzschuch, Wenzel Jakob To cite this version: Guillaume Loubet, Nicolas Holzschuch, Wenzel Jakob. Reparameterizing Discontinuous Integrands for Differentiable Rendering. ACM Transactions on Graphics, Association for Computing Machinery, 2019, 38 (6), pp.228:1 - 228:14. 10.1145/3355089.3356510. hal-02497191 HAL Id: hal-02497191 https://hal.inria.fr/hal-02497191 Submitted on 3 Mar 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Reparameterizing Discontinuous Integrands for Differentiable Rendering GUILLAUME LOUBET, École Polytechnique Fédérale de Lausanne (EPFL) NICOLAS HOLZSCHUCH, Inria, Univ. Grenoble-Alpes, CNRS, LJK WENZEL JAKOB, École Polytechnique Fédérale de Lausanne (EPFL) (a) (b) (c) (d) A scene with complex geometry and visibility (1.8M triangles) Gradients with respect to scene parameters that affect visibility Fig. 1. The solution of inverse rendering problems using gradient-based optimization requires estimates of pixel derivatives with respect to arbitrary scene parameters. We focus on the problem of computing such derivatives for parameters that affect visibility, such as the position and shape of scene geometry (a, c) and light sources (b, d). Our renderer re-parameterizes integrals so that their gradients can be estimated using standard Monte Carlo integration and automatic differentiation—even when visibility changes would normally make the integrands non-differentiable.
    [Show full text]