Imatest-training-class-1-2013原版完整课件

Imatest:

Courseoutline1Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCImatestLLCBoulder,Coloradowww.imatestcomBackground

History–Products/Modules–

WorkflowBasicimageconcepts

Sharpness–gamma–colorspace–

Rawimages&demosaicingImagequalityfactors

–SummaryExample

–

SFRplusmoduleTheImatestLab

EquipmentandSetup

PhotographingImatestchartsImatest:

Courseoutline2Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCImatestsettingsinifileforsettingsOptionsandmenusCommonoperations

–File&ROIselection,dialogboxes,savingresultsImatestmodules

(outline)IntroductionKeyimagequalityfactors:detailedInstructionsRegionselectionandinputoptionsOutput–describedisplays.Livedemonstration/exerciseImatest:

Courseoutline3Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCImatestmodules(bymodule)SFRplusStepchart–DynamicrangeColorcheck–MultichartsDistortionUniformity–Uniformity-

Interactive–BlemishDetectSharpnessmeasurements:SFR–Batchview–MTFCompare–Sharpening–Slanted-edge–SQF/AcutanceRescharts:SFR–SFRplus–Star–LogF–LogF-Contrast–Wedge–Random–AnyscenesharpnessIndustrialTesting(IT)

Non-GUImodulesforindustrialtesting.EXEorDLLversionsPart1:ContentsImatestintroductionBackground/historyProductlineupModulesummaryandworkflowBasicimageconceptsSharpnessintroductionRawfiles&rawconversionImagequalityfactorsFeb.2012Imatest2dayclassNormanKoren©2008-2013,ImatestLLCImatest:

BackgroundFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCCreatedtoenablephotographerstotestlensesandcameras.SharpnessTonalresponseanddynamicrangeColoraccuracyStartedworkJuly2003.Releasedv1.0September2004.Consistsofseveralmodulesthatanalyzeimagesofstandardandcustomtargets.CompiledinMatlab,includesruntimelibraryininstallerpackage(Matlabnotrequired)FrequentenhancementsappliedtotheBetaversion(now3.10-Beta).Imatest:

ProductlineupFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCImatestMaster:Fullfeaturedversionforimagingsystemdevelopers.Forcorporate/businessusers.ImatestIS(ImageSensor):

Interfacesdirectlytomanufacturer’sdevelopmentsystems.Allowsrealtimeupdates.ImatestIT:

Non-GUI(GraphicsUserInterface)DOS-callableEXEandDLLprogramsforautomatedtesting&qualitycontrol.Nowimplementedonproductionlines.ImatestStudio:Everythinganindividualphotographerneedstotestcamerasandlenses.

Onlysoldtoindividualphotographers.Gamutvision

(separateprogram):Analyzetheresponse,colorgamut,andgamutmappingbehaviorofICCprofiles.Shownonright.Gamutvision3DL*a*b*colorgamutSharpnessmodulesFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCModuleImagequalityfactorSharpness(MTF)LateralchromaticaberrationNoiseSFR,SFRplus

(Spatialfrequencyresponse)(StandardorRescharts)LogFrequency

(Rescharts)Lossindetaildue

tosoftware

noisereductionContrast(gamma)StarChart(Rescharts)LogF-Contrast(Rescharts)Colormoiré(Reschartsmoduleshaveahighlyinteractiveinterface.)Wedge(Rescharts)Random/Dead.

Leaves

(Rescharts)OtheranalysismodulesFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCModuleImagequalityfactorColoraccuracyTonalresponseandcontrastDynamicrangeExposureaccuracyLightfalloffLensdistortionNoiseColorcheck,Multicharts

Stepchart,

DynamicRangeSFRplusUniformity,

Uniformity-InteractiveDistortion,DotPatternISOSensitivitySensordefectsBlemishDetectUtilitymodules1Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCTestCharts:Createbitmap

orScalableVectorGraphics

testcharts.

Printingskillrequired.ScreenPatterns:

Displaysalargevarietyoftestpatternsonflatscreenmonitors.View/Renamefiles:RenamefilesusingEXIFdata(addsAperture,ISOspeed,shutterspeed,etc.).Utilitymodules2Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCFindsharpestfiles:

Findthesharpestfile

inagroupoffiles

takenofasimilarimage.

Sharpnessmetricsarenotstandard–forcomparison-only.dcraw:Frontendtodcrawrawconverter.Candemosaicimages(withminimalprocessing)orcreateBayerrawimages.Rawview:DisplaysBayerrawimages.Letsyoucorrelatecolorwithpixellocation.EXIF:ViewdetailedimagefileEXIFdata.Images,imagefiles,andconceptsFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCAnimageisamxnxkarray.mrows(heightinpixels).ncolumns(widthinpixels).k=1formonochrome;3forcolor.eachpixelmaybe8bits(onebyte;24-bitcolor),or16bits(twobytes;48bitcolor).Standardfileformats:TIF,BMP(usuallyuncompressed),JPG(lossycompression;size,qualityselectable),PNG(losslesscompression)Wepresentseveralfile-relatedconcepts.PixelsSpatialandfrequencydomainsFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCAcomplexsignal(audioorimage)canbecreatedbycombiningsignalsconsistingofpuretones(sinewaves),whicharecharacterizedbyaperiod.Frequency

isdefinedas1/period(shorterperiod=higherfrequency.)Thebetterthesystemresponseathighfrequencies(shortperiods),themoredetailthesystemcanconvey.Spatialdomain(theactualimage)andfrequencydomainarerelatedbytheFouriertransform.(we’llomittheequations.)Period

(1cycle)Periodhasunitsoftimeordistance.SpatialfrequencyFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLC1Cycle=1LinePair(LP)=2LineWidths(LW)Thechoiceofunitsdependsonwhatyouwanttomeasure:Howwellarepixelsutilized?Howmuchdetailintheimageasawhole?Howmuchdetailperdistance?SpatialFrequencyf

ismeasuredinCycles(periods)orLineWidthsperdistance,wheredcanbepixels,physicaldistance(mm,inches)on

thesensoror(infrequently)objectPictureHeightAnglePerioddf=1/dSpatialfrequencyf(increaseslogarithmically)KeySharpnessmeasurement:

SFR/MTFSFR(SpatialFrequencyResponse)

MTF(ModulationTransferFunction)

asinepatternatspatialfrequencyfrelativetocontrastatlowspatialfrequencies.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCContrastatf=C(f)=(Vmax-Vmin)/(Vmax+Vmin)forluminanceV.MTF(f)=100%C(f)/C(0)100%atlowspatialfrequenciesBar(showsedges)Original(constantcontrast)MTFdropswithfrequencySine(usedforMTF)isthecontrastofSpatialfrequencyunitsFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLC1Cycle=1LinePair(LP)=2LineWidths(LW)SpatialfrequencyunitsApplicationCycles/pixelShowshowwellpixelsareusedCycles/distance

(cycles/mmor

cycles/inch)Usedinforcomparingresolutionintheolddaysofstandardfilmformats(e.g.,24x36mmfor35mmfilm).LineWidths/Picture

Height(LW/PH)Measuresoverallimagesharpness.TraditionalforTVLinePairs/Picture

Height(LP/PH)Measuresoverallimagesharpness.UsedbyLineWidths/Angle

(mRadordegree)MeasuresangularsharpnessDifferentunitsscaledifferentlywithimagesensorandpixelsize(mxn).Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCMTFdisplay(foratypicaledge)Upper:Averageslantededge

FromISO12233chart,Imatest

SFRpluschart,orbitmaporSVGchartsfromTestCharts

Measure

averageedgeandrisedistanceLower:SFR/MTF(sharpness)curveResultsderivedfromMTF:MTF50,MTF50P,others.Moreextendedresponseisbetter,butcanresultinaliasing–tobediscussedlater.AliasingThesharperthebetter,BUTFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCBadaliasingBayercolorarraysworsensaliasing–colormoiréishighlyvisible.artificiallowfresponseforsignalsabovefN(Moirépatterns).Toomuchresponseabove0.5cycles/pixel(NyquistfrequencyfN)maybeundesirableduetoaliasing:Anti-aliasing(lowpass)filtershelp,butreducesharpness.

LogFrequency

measuresmoiré.Gamma(γ)introductionFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCEncodingDisplayTraditionalmonitorsarenonlinear:

Luminance=pixellevelγ;γ≈2.2Filesmustbeencodedwithapproximateinverseofdisplayresponse(γ≈1/2.2=0.454)Advantageofγ:morelevelsindarkareas(fewerinlightareas);greatereffectivedynamicrangein8-bit(255-level)files.Logarithmic(Log10)LinearGamma(γ)&responsecurvesFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCGammaiscontrast.averageslopeoflogpixelvs.logexposurecurve(H&Dorcharacteristiccurve)“S-curve”or“shoulder”isoftenaddedduringencoding(rawconversion).Reduceschancesofhighlightburnout.ImatestStepchartmeasurescameraresponse.Unlikesharpness,goodnessishardtodefine;dependsonapplication.CameraresponsefromImatestStepchartFilm+paperresponse(S-curvewhencombined)DensityandexposureunitsFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCLogarithmicscalesoftenusedforillumination&pixelstheeye’sresponseislogarithmicPerformanceindarkareasisclearer-3-2-10

Logexposure(-Density)Density=log10(lightin/lightout)(Log10)oftenabbreviatedLog.Logexposure=-targetdensityChangingdensityby1changeslightbyafactorof10Factorof2units:f-stop,EV(ExposureValue),zone1Densityunit=3.32f-stops(EV)Log(pixellevel/255)ColorspaceintroductionFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCMappingbetweenRGBpixelvalues(example:{255,0,0}andperceivedcolors:xy(xyYspace)ora*b*(fromL*a*b*space)Withoutacolorspace,RGBlevelshavenomeaning.Nostandardcolorrepresentation(space)forsensorsMustconvertcolorstoastandardcolorspace(gamutmapping).Colorspacesarecharacterizedbygamut(rangeofcolorsthatcanberepresented).sRGB(lowgamutfromCRT),AdobeRGB(mediumgamut)CIE1931xygamutsofAdobeRGBandsRGB(fromGamutvision)Colorspace:L*a*b*representationFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLC2Da*b*“slice”AdobeRGBandsRGB3DL*a*b*MoreperceptuallyuniformthanxyY(previousslide).DerivedfromY-B,R-Gopponentcolortheory.DistanceinL*a*b*(∆E)isroughlyproportionaltoperceivedcolordifference(therearebettermetrics).L*a*b*Rawfiles:whatthesensorsendsoutFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCRaw(unprocessed)filesfromimagesensorsProprietaryformats(AdobeDNGpossiblestandard.)Bayerfiltered(RGRGRG,GBGBGB…;onecolorperpixel)exceptforFoveonLinearresponse(uptosaturation)NowhitebalanceLittleornonoisereductionorsharpening12or14bitsperpixelNotveryusefuluntilconvertedtoastandardRGBfile4arrangements

(redinRmCn)RawconversionFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCTobeuseful,rawfilesmustbeconvertedtostandard(RGB)fileformats(TIF,JPG,PNG,etc.)Performedonoroffcamera.Fivefunctions.AllaffectImatest

results.Demosaicing:Interpolatesoeachpixelhas3colors.Oftensophisticated,especiallywhendoneoffcamera.Applygamma(γ)curve+tonalresponse(nextslides)Whitebalance&coloradjustment:convert

tostandardcolorspace(typicallysRGB).Sharpen(enhanceedges)Noisereduction(lowpassfiltering;awayfromedges)RGBineachpixelRawfileusageFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCRawfilesareusedtomeasureimagingsystemperformanceatthesensorpixellevelbeforeconversionbecauseallconversionfunctionsaffectimagequality,andhenceImatestmeasurements.tomeasuresensornoise(inMulticharts).byphotographersformaximumperformance

(highestdynamicrange,etc.)ImatestconvertsrawfilestoStandardRGBformatswithminimalprocessingBayerraw:standardfileformatwherepixels

are(mostly)thesameasinrawfiles(nodemosaicing,etc.)RawconversioninImatestFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCdcraw.exeisusedforrawconversion.ThereisaVistaversion.Imatest

hasaGUIfront-endfordcraw/Librawwithmanyoptions.RGBineachpixelImatestconvertsrawfilestoRGBorBayerrawwhenArawfile(CR2,NEF,TIFwithcertainproperties,etc.)isopenedbyanymoduleArawfilewithanextensionspecifiedbygeneralizedreadrawisopened.dcrawiscalled(buttononright)dcrawrawconversionFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCDOSprogramforconvertingcommer-cialrawfileswithminimalprocessing.Allowsyoutomeasureintrinsiccameraperformance:nosharpening,noisereduction,ortonalresponsecurve.Demosaicingisoptional:canconverttoBayerrawdcraw’sGUIfront-endiscalledbydcrawbuttonorwhenrawfileisread.Manyoptions:LivedemoGeneralizedReadRaw

forfilesfromdevelopmentsystemsFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCClickSettings,ReadRawsetuptoopen.Upto8fileextensionscanbespecified(.appshown).Settingsderivedfromdatasheets&trial-and-error.Whitebalance&levelcanbecontrolled.OutputisBayerRawordemosaicedimage.Ifsettingsaren’tcorrect(imagesize~=Width*Height),informationisprovidedtohelpfindcorrectimagedimensions.Rawview:BayerrawfileviewerFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCdcrawcanconverttoBayerrawfiles(undemosaicedTIFF,etc);samepixels(allegedly)asRAWfile.RawviewcandisplayBRfiles:Youcandeterminecolorarrangement(whichpixelisred).BRimagescanbesavedasdemosiacedfilesorasRGBfiles,withonegreenchannel(G(R),G(B),oralternating).Manyoptions:LivedemoImageQualityFactorsSharpnessLateralchromaticaberrationNoiseColoraccuracyTonalresponseandcontrastDynamicrangeExposureaccuracyLightfalloffLensdistortionISOsensitivityFeb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCThisimagefromUtah

willbeusedtoillustrateimagequalitydegradations.Sharpness(MTF/SFR)Derivedfromslanted-edgeorothertargetArguablythemostimportantIQfactorDetermineshowmuchdetailcanbeconveyedAffectedbythelens,sensor,anddigitalsharpening.DependsontargetMTF50,thespatialfrequencyfwhereMTFfallsto50%,isagoodsharpnessindicator.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCSFRresults:MTFtendstodecreasewithspatialfrequency–fasterforblurredimages.original|blurredSFR&othersharp-nessmodulesSFRplusSFRresults:Top:OversharpenededgeBottom:MTFSharpness(oversharpening)Digitalsharpeningenhancesedges;itboostsMTFandmaycausepeaking.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCSFR&othersharp-nessmodulesOversharpeningcausessevere“halos”atedges.Commonincompactdigitalcameras&cameraphones.original|oversharpenedSFRplusTexture(removedbysoftwarenoisereduction)-MTFmeasuredfromthechartsshownbelowcanmeasuretextureloss.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCSignalprocessingisnonuniforminmostconsumercameras:Sharpeningnearedges&contrastyfeatures;Noisereduction(blurring)intextureareasCancauselossoftexturedetail.original|noise-reducedRandom/Dead.

Leaves

(Rescharts)SpilledCoins/

(DeadLeaves)Random/

Scale-invariantLateralChromaticAberration(LCA)Seenas“colorfringing”nearcorners.Canbedigitallycorrected:bestbeforedemosaicing.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCSFR

original|withLCASFRplusNewDotPatternmoduledoesI3ACIPQLCAmeasurement.DotPatternNoiseRandomperturbationsofsignallevel.Aseriousdegradation;correspondstograininfilm.Softwarenoisereductioncanremovefinedetail.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCColorcheck,

MultichartsStepchartStepchartresults,showingnoiseintwodifferentscales.Top:Noiseinf-stops(referencedtosignal).Bottom:Noiseinpixels.original|noisyColoraccuracyUsesimageofGretagMacbethColorChecker.ErrorsdisplayedinL*a*b*space.Feb.2013Imatest2dayclassNormanKoren©2008-2013,ImatestLLCColorcheck,Multi