ScannersCaptureDevicesHomeDepartmentofComputerscannerscapture設(shè)備計(jì)算機(jī)家系

ScannersCaptureDevicesHomeDepartmentofComputerscannerscapture設(shè)備計(jì)算機(jī)家系第1頁/共50頁CULBiasonImageCapture:Createrichimagesthatareusefulovertimeinthemostcost-effectivemanner.SetconversionrequirementsgreaterthanimmediateapplicationPromotereuseofcontentEnablesharingofcomparableandtrustedresourcesacrossdisciplines,users,andinstitutions第2頁/共50頁WhyRichDigitalMasters?PreservationOriginalmayonlywithstandonescanMaintenanceofdigitalfilesCostOnescanmaybeallthatisaffordableConversioncostsdwarfedbyothercostsAccessManyfromoneThericherthefile,thebetterthederivativeintermsofqualityandprocessibility第3頁/共50頁Howtodeterminewhat’sgoodenough?ConnoisseurshipofdocumentattributesIdentifykeyinformationcontentObjectivelycharacterizeormeasureattributes:size,detail,tone,andcolorAppreciateimagingfactorsaffectingqualityandcostTranslatebetweenanaloganddigitalEquatemeasurementstodigitalequivalenciesandcorrespondingmetrics,e.g.,detailsizeresolutionMTF第4頁/共50頁CUL’sApproachtoImaging:“NoMore,NoLess”Imagerequirementsandcostimagequalityandutilitydesiredpointofcapture第5頁/共50頁DigitalImageQualityis

GovernedBy:resolutionandthresholdbitdepthcolormanagementimageenhancementcompressionandfileformatsystemperformance第6頁/共50頁ResolutionDeterminedbynumberofpixelsusedtorepresenttheimageIncreasingresolutionincreaseslevelofdetailcapturedandgeometricallyincreasesfilesizezoomin第7頁/共50頁EffectsofResolution600dpi300dpi200dpi第8頁/共50頁ThresholdSettinginBitonalScanning definesthepointonascalefrom0to255atwhichgrayvalueswillbeinterpretedeitherasblackorwhite第9頁/共50頁10EffectsofThresholdthreshold=100threshold=60第10頁/共50頁BitDepthDeterminedbythenumberofbinarydigits(bits)usedtorepresenteachpixel1-bit8-bit24-bit第11頁/共50頁BitDepthincreasingbitdepthincreasesthelevelofgrayorcolorinformationthatcanberepresentedandarithmeticallyincreasesfilesizeBitdepth,dynamicrange,andcolorappearance第12頁/共50頁UtilizingSufficientBit-Depth3-bitgray8-bitgray第13頁/共50頁UtilizingSufficientBitDepth8-bitcolor24-bitcolor第14頁/共50頁BitDepthvs.DynamicRangeTherangeoftonaldifferencebetweenlightestlightandthedarkestdark第15頁/共50頁MappingTonesCorrectly:UseofHistograms第16頁/共50頁RepresentingColorAppearanceBalancedColorColorShiftTowardsRed第17頁/共50頁ImageEnhancementImageeditingtomodifyorimproveanimagefilters(brightness,contrast,sharpness,blur)toneandcolorcorrectionUseraisesconcernsaboutfidelityandauthenticity第18頁/共50頁EffectsofFiltersnofiltersusedmaximumenhancement第19頁/共50頁ImageEditing第20頁/共50頁Compressionreducesfilesizeforprocessing,storage,transmission,anddisplayimagequalitymaybeaffectedbythecompressiontechniquesusedandthelevelofcompressionapplied第21頁/共50頁CompressionVariableslosslessversuslossycompressionproprietaryvs.openschemeslevelofindustrysupportbitonalvs.gray/colorseeattributesofcommoncompressiontechniquesat:/preservation/tutorial/presentation/table7-3.html第22頁/共50頁EffectsofJPEGCompression300dpi,8-bitgrayscaleuncompressedTIFFJPEG18.5:1compression第23頁/共50頁Compression/FileFormatComparisonGIF(lossless)FileSize:60KBJPEG(lossy)FileSize:49KBimagescourtesyofEdisonPapers第24頁/共50頁FileFormatsConsistofboththebitsthatcompriseimageinformationandheaderinformationonhowtoreadandinterpretthefileImagequalityaffectedbyformatsupportfor:BitdepthCompressiontechniquesColormanagementHardware,software,andnetworksupportSeecommonfileformatschartat:/preservation/tutorial/presentation/table7-1.html第25頁/共50頁EquipmentusedanditsperformanceovertimescannerswithsamestatedfunctionalitycanproducedifferentresultsFactorsaffectingimagequality:Optical,mechanical,andsensingcomponentsCalibrationAgeofequipmentEnvironment第26頁/共50頁300dpi,scannerA300dpi,scannerBVariationsinImageQualityduetoScannerPerformance第27頁/共50頁CorrelatingDocumentAttributestoImageRequirementsExample:DeterminingResolutionRequirementsWhat’syoufinestfeature?What’syourqualityrequirement?What’syourimagingapproach?第28頁/共50頁CaseStudy:BrittleBooksVariables:featuresize,quality,imagingapproachfixedmetric:smallestlowercaseletterQIvalues:8(excellent),5(good),3.6(marginal)Resolutionkeytotextcapture,e.g.,dpiBitonalQIformulafortextDPI=3QI/.039h600dpi1-bitcaptureadequatelypreservesinformationalcontentofcleanlyproducedtextandsupportsimageprocessing(e.g.,OCR)第29頁/共50頁第30頁/共50頁第31頁/共50頁TextualDocumentsMayRequireTonalCapturePagesbadlystainedPagesexhibitlowcontrastbetweentextandbackgroundFinefeaturesnotfullyresolvedPagescontaincomplexgraphics,colororimportantcontextualinformationGray/colorQIformulafortextDpi=2QI/.039h第32頁/共50頁DeterminingResolutionRequirementsbeyondTextStrokewidthFinestscaleVisualperception第33頁/共50頁DefiningDetailasStrokeEdge-basedrepresentationsVariables:featuresize,quality,imagingapproachfixedmetric:widthoffinestline,stroke,dot,ormarkingQIvaluesbasedonsamplingfrequency:2(excellent),1.5(good),1(marginal)Resolutionandbitdepthkeytoquality第34頁/共50頁DefiningDetailasStrokeQIformulasforstrokeGray/color:dpi=QI/.039w

QI=dpix.039wBitonal:dpi=(1.5QI)/.039w第35頁/共50頁AdequatelyRenderedStroke第36頁/共50頁InadequatelyRenderedStroke第37頁/共50頁ExampleManuscriptpagewithfinestsignificantstrokemeasuring.2mm,whichmustbefullycapturedGray/color:dpi=QI/.039wQI=2,w=.2Dpi=2/[.039(.2)]=256dpi第38頁/共50頁DefiningDetailasScaleSmallestsignificantscaleorrepeatablepattern,e.g.,knotsinarugvs.strandsinthethreadCanresultinveryhighresolutionrequirements(e.g.,photographs,bookillustrations)Halftones:scanat4timesthescreenruling,utilizespecialdescreen/rescreening,orscaningrayscale(400dpiisagooddefault)第39頁/共50頁HalftoneScannedat150DPI第40頁/共50頁HalftoneScannedat400DPI第41頁/共50頁DefiningDetailBasedonVisualPerceptionHumaneyecandetectdetailsapproximately1/215inchwideFinerdetailsareopticallyaveragedUsingtwopixelrule,visualperceptionrequirementsmetat430dpiIllustratedBookStudy:400dpigrayscalerecommendation第42頁/共50頁/preservation/illbk/AdComm.htmy.第43頁/共50頁DetailRepresentedat400dpi

第44頁/共50頁TranslatingBetweenDigitalResolutionandScannerPerformanceDetailcapturegovernedbyresolution,threshold,bit-depth,andsystemperformanceSamplingresolution(DPI)isnotatrueindicatorofimagequality,althoughitmaysufficeforscanninginthe300-600dpirangeMonitorEmergingSystemPerformanceMetrics(e.g.,MTF)第45頁/共50頁AligningDocumentAttributeswithDigitalRequirementsIdentifykeydocumentattributesTone,color,anddetailCharacterizethem,ifpossiblethroughobjectivemeasurementsDeterminequalityrequirementsandtolerancelevelsTranslatebetweenanaloganddigitalandbetweenscanningrequirementsandscanningperformance第46頁/共50頁AligningDocumentAttribu