MITMAS_531F09_lec05_notes

MITMAS_531F09_lec05_notes - ClassNotesOctober9th2009...

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Unformatted text preview: ClassNotesOctober9th2009 ComputationalCamera TraditionalPhotography Photographersmaketheirtermssoundveryexotic.Fstopforexampleiscomplicatedand itiswrong,sotrytousesimplerlanguagetodescribe.Numericalapertureisusedin microscopy,whichismoreexact. Howtocapturetheentireworld Whyisarayis5Dandnot6D?Becausethereisnorollaroundtheray.Itcanbe4Difthere arenooccludingobjects.Canbedescribedas2dpositionoftwopointsontwoplains,or2d positionand2drotation Ifraysareparalleltoaplaneitishardtorepresentitin4D. CameraArrays ForacameraArea: EverycamerapositionisdefinedinUVcoordinates,andeachcamerasimagebuffer capturesintheSTplane. Raysarenotcapturediftheypassinbetweenthecameras Reallytheworldis4dnot3d,becauseitmatterswherethevieweristoo Thedifferencebetweenagiantlensandacameraareaisthatalensisreallysections ofaprism,andinthecameraareacaseitismoreofapinholearea 4Dcapturesallofthegeometricpropertiesofwhateverisseenthroughthelens HereyoucanseethatanoutoffocusobjectcreatesadiagonallineintheXThetagraph,soto refocustheimagetothatplaneyouhavetoessentiallyshiftthecamerasinacameraarraytothat diagonalline. Howyoushiftandaddthepixelsyoucapturedwiththelensletarraychangeswherethe planeoffocusesis.Ifyouwanttofocusatinfinity,justsumallcameras. Ifyouwanttofocusonadifferentplaneyouneedtoshifteachimagebyalittle. Whydoestraditionalcameranotcapturealightfield?Becauseitisonlycapturingthesum oftherayshittingapoint,notthevalueofeachray. Multipleraysyoucancapturea4dlightfield:timemultiplexing,spatialmultiplexing(give upspatialresolutionforangularresolution) Thegraphontheleftrepresentsacamerawithalensandalensletarrayandontherightit representsabaresensorandalensletarray.Thereisatradeoffbetweenangular resolutionandspatialresolution. WaverepresentationofLight Whenripplesareclosetheyarecurved,butfurtherouttheyappearflat. Torefocustheparallelraysalensisused Hereyoucanseethatclosetoalightsourcethereisalotofangularinformation,but furtherawayitismorespatial. Heatintheaircausestheretoberegionsofdifferentdensitiesofair.Pocketsofhotairend upeffectivelycreatinglenseswhichdistortlight.Thisissimilartowhathappenswhenyou seeheatrisingonthestreetanditlookslikewater. Thissameeffectcreatesmirrages Thesedeformedwavesduetoatomospherecreateproblemsfortelescopes,soadaptive lenseswerecreates.Theselensesaredeformableandchangeshapetomakethedeformed wavesparallelagain. Whencorrectingshape(phase)ofawavefrontPhasewrappingoccurs,becausecanonly capturemodularof2pi. Youcanuseamaskovertheaperturetoeffectivelytakemultipleimages,from slightlydifferentviews,usingthesamesensorandlens.Thisiswhatapinholearray accomplishes. MIT OpenCourseWare http://ocw.mit.edu MAS.531 / MAS.131 Computational Camera and Photography Fall 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms. ...
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