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ComputationalPhotographyandVideo
Prof.MarcPollefeys
Dr.GabrielBrostow
Todaysschedule
IntroductionofComputationalPhotography Coursefacts Syllabus DigitalPhotography
Whatiscomputationalphotography
Convergenceofimageprocessing,computervision,computergraphicsandphotography
Digitalphotography: Simplyreplacestraditionalsensorsandrecordingbydigitaltechnology
Involvesonlysimpleimageprocessing Computationalphotography
Moreelaborateimagemanipulation,morecomputation
Newtypesofmedia(panorama,3D,etc.) Cameradesignthattakecomputationintoaccount
(severalslidesinspired/borrowedfromFredoDurand,MIT)
Tonemapping
Before After
DurandandDorsey.Siggraph02
http://www-users.mat.uni.torun.pl/~olka/http://www.loc.gov/exhibits/empire/
Flash/NoFlash
Petschniggetal.Siggraph04
Photomontage
Agarwalaetal.Siggraph04
Panoramicimages
BrownandLoweICCV03
Defocusmatting
McGuireetal.Siggraph05
Videotextures
Schoedletal.Siggraph00
Motionmagnification
Liuetal.Siggraph05
Todaysschedule
IntroductionofComputationalPhotography Coursefacts Syllabus DigitalPhotography
Administrivia
Staff Prof.MarcPollefeys Dr.GabrielBrostow RolandAngst
Timeandlocation: Lectures:Wednesday1315inCABH57 Exercises:Thursday1112inCABH56
Webpage:http://www.inf.ethz.ch/personal/pomarc/courses/CompPhoto/
http://www.inf.ethz.ch/personal/pomarc/courses/CompPhoto/
Courseorganization
Lectures Exercises
Firstafewassignments Laterprojectandpaperpresentations
Smallclassproject Individualorsmallgroups
Gradingpolicy
50%assignments 10%paperpresentation 40%classproject(report+presentation) Bonusforparticipation
Noseparateexam
Textbook
Notextbookrequired Slidesavailableoncoursewebpage Lotmoreresourcesonline
Interestingreference:ComputationalPhotography:MasteringNewTechniquesforLenses,Lighting,andSensors.RaskarandTumblin,toappearsoon,AKPeters.
Todaysschedule
IntroductionofComputationalPhotography Coursefacts Syllabus DigitalPhotography
Topics
Imageformation,Imagesensor,Optics Pixelresolution,Exposure,Aperture,Focus,DynamicRange Color,whitebalance,Bayerpattern,demosaicking, Motionblur,shutter,deblurring Dynamicrange,HDRimaging,tonemapping,bilateralfiltering Imagepyramids,opticalflow,gradients Mattingandcompositing,graphcuts Warpingandmorphing,panoramas Texturesynthesis Illumination,flash/noflash,depthedges Codedaperture,defocus Videotextures,timelapse,videosummarization Lightfield imaging
Todaysschedule
IntroductionofComputationalPhotography Coursefacts Syllabus DigitalPhotography
Overview
Lensandviewpointdetermineperspective Apertureandshutterspeeddetermineexposure Apertureandothereffectsdeterminedepthoffield Sensorrecordsimage
(thisandfollowingslidesborrowedfromFredoDurand,MIT)
Reference
http://en.wikipedia.org/wiki/Lens_(optics)
Theslidesuseillustrationsfromthesebooks
http://en.wikipedia.org/wiki/Lens_(optics)
Morereferences
Plan
Pinholeoptics Lenses Exposure
Whyistherenoimageonawhitepieceofpaper?
Itreceiveslightfromalldirections
FromPhotography,Londonetal.
Pinhole
FromPhotography,Londonetal.
Focallength
pinhole
Film/sensor scene
f
s
Focallength:pinholeoptics
Whathappenswhenthefocallengthisdoubled? Projectedobjectsize Amountoflightgathered
pinhole
Film/sensor scene
f d
s
2f
isdoubledisdividedby4
Questions?
Pinholesize?
FromPhotography,Londonetal.
Diffractionlimit
Optimalsizeforvisiblelight:sqrt(f)/28(inmillimiters)wherefisfocallength
FromWandell
Problemwithpinhole?
Notenoughlight! Diffractionlimitssharpness
Solution:refraction!
FromPhotography,Londonetal.
Lenses
gathermorelight!
Butneedtobefocused
FromPhotography,Londonetal.
Thinlensoptics
Simplificationofgeometricalopticsforwellbehavedlenses Allparallelraysconvergetoonepointonaplanelocatedatthe
focallengthf
Allraysgoingthroughthecenterarenotdeviated Hencesameperspectiveaspinhole
f
Howtotracerays
Startbyraysthroughthecenter
Howtotracerays
Startbyraysthroughthecenter Choosefocallength,traceparallels
f
Howtotracerays Startbyraysthroughthecenter Choosefocallength,traceparallels Yougetthefocusplaneforagivensceneplane
Allrayscomingfrompointsonaplaneparalleltothelensarefocusedonanotherplaneparalleltothelens
f
Focusing
Tofocuscloserthaninfinity Movethesensor/filmfurther thanthefocallength
f
Thinlensformula
fDD
Thinlensformula
fDD
Similartriangleseverywhere!
Thinlensformula
fDD
Similartriangleseverywhere!
y
y
y/y=D/D
Thinlensformula
fDD
Similartriangleseverywhere!
y
y
y/y=D/D
y/y=(Df)/D
Thinlensformula
fDD
1D D
1 1f
+ =
Minimumfocusingdistance
Bysymmetry,anobjectatthefocallengthrequiresthefilmtobeatinfinity.
sensor
Raysfrominfinity
Raysfromobjectatf
Extensionstubes
Allowustoputsensorfartherfocuscloser
Fieldofview&focusing
Whathappenstothefieldofviewwhenonefocusescloser? It'sreduced
sensorfocused at infinity
sensorfocused close
Questions?
http://www.pinhole.cz/en/pinholecameras/dirkon_01.html
Focallengthinpractice
24mm
50mm
135mm
Perspectivevs.viewpoint
Telephotomakesiteasiertoselectbackground(asmallchangeinviewpointisabigchangeinbackground).
Perspectivevs.viewpoint
Movescameraasyouzoomin HitchcockVertigoeffect
Perspectivevs.viewpoint
Portrait:distortionwithwideangle Why?
Wideangle Standard Telephoto
Focallength&sensor Whathappenswhenthefilmishalfthesize? Application:
Realfilmis36x24mm Onthe20D,thesensoris22.5x15.0mm Conversionfactoronthe20D? OntheSD500,itis1/1.8"(7.18x5.32mm) Whatisthe7.723.1mmzoomontheSD500?
pinhole
Film/sensor
scene
f d
s
Sensorsize
Similartocropping
source:canonredbook
http://www.photozone.de/3Technology/digital_1.htm
Recap
Pinholeisthesimplestmodelofimageformation Lensesgathermorelight
Butgetonlyoneplanefocused Focusbymovingsensor/film Cannotfocusinfinitelyclose
Focallengthdeterminesfieldofview Fromwideangletotelephoto Dependsonsensorsize
Moreinthelenslecture
Questions?
Exposure
Gettherightamountoflighttosensor/film Twomainparameters:
Shutterspeed Aperture(areaoflens)
Shutterspeed
Controlshowlongthefilm/sensorisexposed Prettymuchlineareffectonexposure Usuallyinfractionofasecond:
1/30,1/60,1/125,1/250,1/500 Getthepattern?
Onanormallens,normalhumanscanhandholddownto1/60 Ingeneral,theruleofthumbsaysthatthelimitistheinverseoffocallength,e.g.1/500fora500mm
Maineffectofshutterspeed
Motionblur
FromPhotography,Londonetal.
Effectofshutterspeed
Freezingmotion
1/125 1/250 1/500 1/1000
Walking people Running people Car Fast train
Shutter
Varioustechnologies Goal:achieveuniformexposureacrossimage
FromCameraTechnology,Goldberg
Flashsynchspeed?
Fastestshutterspeedforwhichtheshutteropenscompletelyatsomeinstant.
Forfasterspeeds,itopensandclosesatthesametimeandexposesaslit.
Modernhighspeedflashsynchusesmultipleflashbursts
FromPhotography,Londonetal.
Aperture
Diameterofthelensopening(controlledbydiaphragm) Expressedasafractionoffocallength,infnumber
f/2.0ona50mmmeansthattheapertureis25mm f/2.0ona100mmmeansthattheapertureis50mm
Disconcerting:smallfnumber=bigaperture Whathappenstotheareaoftheaperturewhengoingfromf/2.0to
f/4.0? Typicalfnumbersare
f/2.0,f/2.8,f/4,f/5.6,f/8,f/11,f/16,f/22,f/32 Seethepattern?
Maineffectofaperture
Depthoffield
FromPhotography,Londonetal.
Depthoffield
lenssensor
Pointinfocus
Objectwithtexture
Depthoffield
lenssensor
Pointinfocus
Objectwithtexture
Weallowforsometolerance
lenssensor
Pointinfocus
Objectwithtexture
Maxacceptablecircleofconfusion
Depthoffield
Depthoffocus
Depthoffield
Whathappenswhenweclosetheaperturebytwostop? Aperturediameterisdividedbytwo Depthoffieldisdoubled
lenssensor
Pointinfocus
Objectwithtexture
Diaphragm
Depthoffield
FromPhotography,Londonetal.
Depthoffield&focusingdistance
Whathappenswhenwedividefocusingdistancebytwo? Similartriangles=>dividedbytwoaswell
lenssensor
Pointinfocus
Halfdepthoffield
Halfdepthoffield
Depthoffield&focusingdistance
Whathappenswhenwedividefocusingdistancebytwo? Similartriangles=>dividedbytwoaswell
FromPhotography,Londonetal.
SLRviewfinder&aperture
Bydefault,anSLRalwaysshowsyouthebiggestaperture
Brighterimage Shallowdepthoffieldhelpjudgefocus Depthoffieldpreviewbutton:
Stopsdowntotheapertureyouhavechosen Darkerimage Largerdepthoffield
Questions?
Exposure
Twomainparameters: Aperture(infstop) Shutterspeed(infractionofasecond)
ReciprocityThesameexposureisobtainedwitanexposuretwiceaslongandanapertureareahalfasbig
Hencesquarerootoftwoprogressionoffstopsvs.poweroftwoprogressionofshutterspeed
Reciprocitycanfailforverylongexposures
FromPhotography,Londonetal.
Reciprocity
Assumeweknowhowmuchlightweneed Wehavethechoiceofaninfinityofshutterspeed/aperturepairs
Whatwillguideourchoiceofashutterspeed? Freezemotionvs.motionblur,camerashake
Whatwillguideourchoiceofanaperture? Depthoffield,diffractionlimit
Oftenwemustcompromise Openmoretoenablefasterspeed(butshallowDoF)
FromPhotography,Londonetal.
FromPhotography,Londonetal.
FromPhotography,Londonetal.
Questions?
Metering
Photosensitivesensorsmeasuresceneluminance UsuallyTTL(throughthelens) Simpleversion:centerweightedaverage
Assumption?Failurecases? Usuallyassumesthatasceneis18%gray Problemwithdarkandbrightscenes
FromPhotography,Londonetal.
Metering
Centeredaverage
Spot
Smartmetering Nikon3Dmatrix Canonevaluative
Incident Measureincominglight
Fromtheluminouslandscape
Nextslide
ChoiceonNikon
http://www.mir.com.my//
Nikon3DColorMatrix
http://www.mir.com.my/rb/photography/hardwares/classics/NikonF5/metering/
Learningfromdatabaseof30,000photos
Multiplecaptors(segments) Exposuredependson
Brightnessfromeachsegments Color Contrast Distance Focus(whereisthesubject)
Exposure&metering
Thecamerameteringsystemmeasureshowbrightthesceneis InApertureprioritymode,thephotographersetstheaperture,
thecamerasetstheshutterspeed
InShutterspeedprioritymode,thephotographerssetstheshutterspeedandthecameradeducestheaperture
Inbothcases,reciprocityisexploited InProgrammode,thecameradecidesbothexposureand
shutterspeed(middlevaluemoreorless)
InManual,theuserdecideseverything(butcangetfeedback)
Prosandconsofvariousmodes
Aperturepriority Directdepthoffieldcontrol Cons:canrequireimpossibleshutterspeed(e.g.withf/1.4fora
brightscene) Shutterspeedpriority
Directmotionblurcontrol Cons:canrequireimpossibleaperture(e.g.whenrequestinga
1/1000speedforadarkscene) Notethatapertureissomewhatmorerestricted
Program Almostnocontrol,butnoneedforneurons
Manual Fullcontrol,buttakesmoretimeandthinking
Recap:Metering
Measurescenebrightness Someadvancedmodesthattakemultiplesourcesofinformation
Stillanopenproblem
Questions?
Sensitivity(ISO)
Thirdvariableforexposure Lineareffect(200ISOneedshalfthelightas100ISO) Filmphotography:tradesensitivityforgrain
Digitalphotography:tradesensitivityfornoise
From
dpreview.com
Computational Photography and Video Todays scheduleWhat is computational photographyTone mappingFlash/No-FlashPhotomontagePanoramic imagesDefocus mattingSlide Number 9Video texturesMotion magnificationTodays scheduleAdministriviaCourse organizationGrading policyTextbookTodays scheduleTopics Todays scheduleOverviewReferenceMore referencesPlanWhy is there no image on a white piece of paper?PinholeFocal lengthFocal length: pinhole opticsQuestions?Pinhole size? Diffraction limitProblem with pinhole?Solution: refraction!Lenses Thin lens opticsHow to trace raysHow to trace raysHow to trace raysFocusingThin lens formulaThin lens formulaThin lens formulaThin lens formulaThin lens formulaMinimum focusing distanceExtensions tubesField of view & focusingQuestions?Focal length in practicePerspective vs. viewpointPerspective vs. viewpointPerspective vs. viewpointFocal length & sensorSensor sizehttp://www.photozone.de/3Technology/digital_1.htmRecapQuestions?ExposureShutter speedMain effect of shutter speedEffect of shutter speedShutter Slide Number 63Flash synch speed?ApertureMain effect of apertureDepth of fieldDepth of fieldSlide Number 69Depth of fieldDepth of fieldDepth of field & focusing distanceDepth of field & focusing distanceSLR viewfinder & apertureQuestions?ExposureReciprocitySlide Number 78Slide Number 79Slide Number 80Questions?MeteringSlide Number 83MeteringNikon 3D Color MatrixExposure & meteringPros and cons of various modesRecap: MeteringQuestions?Sensitivity (ISO)