Sea Ice Image Processing with MATLAB® Signal and Image Processing of Earth Observations Series Series Editor C.H. Chen Published Titles Sea Ice Image Processing with MATLAB® Qin Zhang and Roger Skjetne Compressive Sensing of Earth Observations C.H. Chen Radar Imaging for Maritime Observation Fabrizio Berizzi, Marco Martorella, and Elisa Giusti Principles of Synthetic Aperture Radar Imaging: A System Simulation Approach Kun-Shan Chen Remote Sensing Image Fusion Luciano Alparone, Bruno Aiazzi, Stefano Baronti, and Andrea Garzelli Sea Ice Image Processing with MATLAB® Qin Zhang and Roger Skjetne MATLAB• is a trademark of The MathWorks, Inc. and is used with permission. The MathWorks does not warrant the accuracy of the text or exercises in this book. This book’s use or discussion of MATLAB• software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of the MATLAB• software. CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2018 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper Version Date: 20180129 International Standard Book Number-13: 978-1-1380-3266-8 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Dedication This isa reallyelaboratebookfor theimageprocessingtoextractice informationsuchasiceconcentration,icefloes sizedistribution,and icetype. To myknowledge, thisis thefirstworkthatattemptstofind themethodtoobtainicefloesizedistributionina systematicand sophisticatedway. Nowadays theiceconcentrationdataona global scalehasbecomeavailableonadailybasisduetothedevelopmentof microwavesatellitesensors. Accordingto thisinnovation,ithas becomepossibleto monitorthevariabilityofsea iceextent ona globalbasis. However, itisstillabig issuetopredict thesea ice behaviorinthenumericalsea icemodelduetothelackofour knowledgeaboutthesub-gridscaleinformationofsea ice. To solve this,theattentiontoicefloesizedistributionhasrecently been increasing. Not limitedto theclimateproblem,sea iceinformationon a sub-gridscaleis alsoan importantissueto themaintenanceof the infra-structurebuiltinthepolarocean. Despiteitsimportance,oneof thebiggestproblemshasbeen thedifficultyin imageprocessing analysis. Sincesea iceisa complicatedmatrix,itis noteasyto analyzetheseaice imagesquantitatively. Thishas hamperedour understandingof thesea icepropertiesona sub-gridscale. Thisbook aimsatsolvingthisproblemand hasachievedittosomeextent by elaboratelyexaminingthepreviousmethodsusinga tankmodeland improvingthesocalled thegradientvector flowsnakealgorithmfor thereal iceconditions. This workcertainlycontributesto thisissue andshedslighton collectingobservationaldataon anoperational basis. Therefore, Ihighlyevaluatethisworkandhopethealgorithm developedbytheauthorswillbeused toimproveourunderstanding of seaiceproperties. — Takenobu Toyota Instituteof LowTemperatureScience HokkaidoUniversity Contents Foreword................................................................................................................xiii Preface.....................................................................................................................xv Acknowledgments.................................................................................................xix Contributors..........................................................................................................xxi ListofFigures......................................................................................................xxiii ListofTables........................................................................................................xxix Chapter1 Introduction.....................................................................................1 1.1 Researchbackground..............................................................1 1.2 Seaiceparameters..................................................................3 1.2.1 Iceconcentration........................................................3 1.2.2 Icetypes.....................................................................4 1.2.3 Icefloesizeandfloesizedistribution........................4 1.3 Applicationsofdigitalimageprocessingtechniquesfor iceparameteridentification.....................................................5 1.3.1 Iceconcentrationcalculation.....................................5 1.3.2 Seaicetypeclassification..........................................6 1.3.3 Icefloeidentification..................................................7 1.4 Bookscopeandstructure........................................................8 Chapter2 DigitalImageProcessingPreliminaries........................................11 2.1 Imagetypes...........................................................................11 2.1.1 Grayscaleimage.......................................................11 2.1.2 Colorimage..............................................................13 2.1.2.1 TheRGBcolorspace...............................13 2.1.2.2 TheCMYandCMYKcolorspaces........13 2.1.2.3 TheHSIcolorspace................................15 2.1.3 Indexedimage..........................................................15 2.2 Imagehistogram...................................................................16 2.3 Basicrelationshipsbetweenpixels.......................................17 2.3.1 Pixelneighborhoods.................................................17 vii viii Contents 2.3.2 Adjacency................................................................18 2.3.3 Path..........................................................................19 2.3.4 Connectivity.............................................................19 2.3.5 Regionandboundary...............................................19 2.4 Distancetransform................................................................20 2.4.1 Euclideandistance...................................................21 2.4.2 City-blockdistance..................................................21 2.4.3 Chessboarddistance.................................................22 2.4.4 Performanceofthedistancemetrics........................22 2.5 Convolution...........................................................................22 2.6 Setandlogicaloperations.....................................................24 2.6.1 Setoperationsonbinaryimages..............................24 2.6.2 Setoperationsongrayscaleimages.........................27 2.6.3 Logicaloperations....................................................28 2.7 Chaincode............................................................................29 2.8 Imageinterpolation...............................................................32 2.8.1 Nearestneighborinterpolation.................................33 2.8.2 Bilinearinterpolation...............................................33 2.8.3 Bicubicinterpolation................................................35 Chapter3 IcePixelDetection.........................................................................37 3.1 Thresholding.........................................................................37 3.1.1 Globalthresholding..................................................38 3.1.1.1 Otsuthresholding.....................................40 3.1.2 Localthresholding...................................................43 3.1.3 Multithresholding.....................................................44 3.2 Clustering..............................................................................46 3.2.1 Clusteringtypes.......................................................47 3.2.2 K-meansclustering..................................................48 3.3 Experimentresultsanddiscussion........................................52 Chapter4 IceEdgeDetection........................................................................59 4.1 Derivativeedgedetection......................................................59 4.1.1 Gradientoperator.....................................................59 4.1.2 Laplacian..................................................................63 4.2 Morphologicaledgedetection..............................................66 4.2.1 Erosionanddilation.................................................67 4.2.1.1 Binaryerosionanddilation.....................68 4.2.1.2 Grayscaleerosionanddilation................69 4.2.2 Morphologicalclosingandopening.........................71 4.2.2.1 Morphologicalclosing.............................71 4.2.2.2 Morphologicalopening...........................73 4.2.3 Morphologicalreconstruction..................................73 4.2.3.1 Binarymorphologicalreconstruction......73 Contents ix 4.2.3.2 Grayscalemorphologicalreconstruction.75 4.2.4 Morphologicalgradient............................................77 4.3 Experimentalresultsanddiscussion.....................................78 Chapter5 Watershed-BasedIceFloeSegmentation......................................83 5.1 Watershedsegmentation.......................................................84 5.1.1 Watershedsegmentationusinggradients.................89 5.1.2 Watershed segmentation using the distance transform..................................................................90 5.1.3 Marker-controlledwatershedsegmentation.............95 5.2 Combination of the watershed and neighboring-region mergingalgorithms...............................................................96 5.2.1 Concavedetectionbychaincode.............................99 5.2.1.1 Boundarytracing.....................................99 5.2.1.2 Differentialchaincode..........................103 5.3 Experimentalresultsanddiscussion...................................104 Chapter6 GVFSnake-BasedIceFloeBoundaryIdentificationandIce Im- ageSegmentation.........................................................................109 6.1 Traditionalparametricsnakemodel...................................110 6.1.1 Theenergyfunctionals...........................................111 6.1.1.1 Internalenergy.......................................111 6.1.1.2 Externalenergy......................................113 6.1.2 Implementation......................................................115 6.1.3 Limitations.............................................................122 6.2 Gradientvectorflow(GVF)snake......................................123 6.3 Contours initialization for applying the GVF snake al- gorithminicefloeboundaryidentification.........................128 6.3.1 Thelocationofinitialcontour................................129 6.3.2 Theshapeandsizeoftheinitialcontour...............131 6.3.3 Automatic contour initialization based on the distancetransform..................................................133 6.4 Iceimagesegmentation......................................................135 6.5 Discussion...........................................................................137 6.5.1 Stoppingcriterionforthesnake.............................137 6.5.2 GVFcapturerange.................................................138 6.5.3 Bordereffects.........................................................139 Chapter7 SeaIceTypeIdentification..........................................................145 7.1 Iceshapeenhancement.......................................................145 7.1.1 Morphologicalcleaning.........................................146 7.1.2 Connectedcomponentextractionandlabeling......146 7.1.3 Holefilling.............................................................147