Image Quality—Factors affecting image quality

[Pages:20]ThistechnicalbriefprovidesdetailedinformationontheImageQuality,Performance,andFlexibilityofEpson Scanners.

ImageQuality--Factorsaffectingimagequality

Whencomparingscanners,hardwareresolutionandcolorpixeldeptharetwofeaturesoftenusedtogauge imagequality.Thesetwofeaturesareimportant,butthereareanumberoffactorsthatdetermineimage qualityinascanner,suchasthefollowing:(Manyoftheseelementswillbediscussedindetailinupcoming sectionsofthisdocument.)

Precisionsteppermotor forhighqualitysub-scan

resolution

Opticalresolutionand colorbitdepth

Dynamicrangecontrol

Typeoflampsystemused

QualityoftheAnalogtoDigitalconverter(ADC);Epsonscannershave optimumperformanceforminimal noiseandtightcolorregistration.

Typeoffocusmethod

Opticsystem

Colorvs.monochromeCCD

TheEpsonExpression?andGTseriesscannersareEpson'sprofessionalseriesscannersdesignedforexcellencewithrespecttoimagequality,speed,usability,versatility,anddurability.Thesescannersincludethe highestqualitycomponents.

TheEpsonPerfection?seriesscannersaredesignedforhomeandentry-levelcorporateandgraphicsarts users,andaredesignedwiththehighestqualitycomponentsintheirpriceclass.

ImageQuality--Resolution

Ascanner'sresolutiondeterminestheamountofdatathatisreadbythescanner.Asresolutionincreases,so doesthefilesize.Resolutionismeasuredinavarietyofways.

1.Opticalresolution:ThisistheactualnumberofpixelsreadbytheCCD(ChargeCoupledDevice),which measurestheintensityofthelightthatisreflectedfromtheimagetobescanned,andconvertsittoan analogvoltage.Ifascannerhasaresolutionof600x2400dpi,itsopticalresolutionis600dpi,which meansthatitcanresolve600bitsofdataperinch.

2.Hardwareresolution:Usingaprecisionsteppermotortodouble-stepor quadruple-stepthecarriage,thescanner'ssub-scannerresolutioncanbe increased.Forexample,ascannercanhaveanopticalresolutionof1200 dpi,butahardwareresolutionof1200x2400dpi(becauseitdouble-steps thecarriagetoincreasetheverticalresolution).

1200dpi

2400dpi

ScannerTechnicalBrief--Page1

6/07

ImageQuality--Resolution(cont.)

3.Interpolatedresolution:Interpolationisamethodtoincreasetheresolutionofanimage.Itusesa complexalgorithmto"add"pixelstoanimagebasedonthemathematicalprobabilityofsurrounding pixels.

Forexample,ifascannerhasahardwareresolutionof1200x2400dpi,andamaximumresolutionof 9600x9600dpi,thescanningsoftwareusesinterpolationtocreatescannedimageswithresolutions greaterthanthehardwareresolution.

4.Benefitsofhigheropticalresolution:Higherresolutionallowsyoutoscanthefollowingtypesofimageswithoutusinginterpolation.Usingactualimagedatainsteadofinterpolateddataresultsinmore accurateimages.

LineArt Whenscanningblackandwhitelineart,imagepixelstranslateexactly totheprinteddots.Therefore,highresolutionisrequiredtocapture andprintthesharplinesandedgesofanimage.

2x2.5inch imagescanned at1200dpi

Ifenlargedto8x

10inches,effective

resolution:300dpi

Enlargingasmalloriginal Inordertocaptureenoughdetailtoenlargeanimage,youmust increasethescannedresolutioninproportiontotheincreaseinimage size.Ifyoudon't,thenyouwillhavetointerpolateimagedatato maintainthesameresolutioninthelargerimage.

Precisepixelediting Manygraphicartistsscanimagesathighresolutionsforprecisepixel editing.Itisalwaysbettertocapturetheimagedatawhentheimage isbeingscannedandusetrueimagedatathantouseinterpolationif moredataisneededlater.

ImageQuality--Pixeldepth

Pixeldepthreferstothenumberofbitsofdatacapturedforeachpictureelement(pixel).Eachpixelcan havetwostates(OnorOff );thereforethenumberofcolorsorgrayscalesthatascannercanrecognizeis computedbytakingthepizeldepthasanexponentoftwo.Thefollowingchartsliststhenumberofcolors recognizedforeachdifferentscanmode.

Scanmode

Numberofcolorsrecognized

Bi-level(1bitperpixel) 21=2colors(blackandwhite)

8-bitgrayscale 28=256shadesofgray

10-bitgrayscale 210=1,024shadesofgray

8-bitcolor(indexedcolor) 28=256colors

24-bitRGB(8bitsperpixel,percolor) 224=16.7millionscolors

36-bitRGB(12bitsperpixel,percolor 236=Over68billioncolors

48-bitRGB(16bitsperpixel,percolor) 248=Over250trillioncolors

ScannerTechnicalBrief--Page2

6/07

ImageQuality--Pixeldepth(cont.)

AllEpsonscannershavea42-bitor48-bitcolordepth.butsomeofthemodelssupport24-bitexternalcolor depth,whichisthedatathatissentfromthescannertothecomputer.Herearethedifferencesbetween outputcolordepth:

KeyDifferences 42-bit,or48-bitInternal/24-bitExternalColor 36-bit,42-bit,or48-bitInternalandExternal

Depth

ColorDepth

Howitworks Thescannercaptures42-,or48-bitimage Thescannercaptures36-,42-,or48-

data,but"downsamples"animageto

bitimagedataandoutputsalldatatoa

24-bits,keepingthemostsignificantcolor softwareaplicationthatsupports48-bit

data.

imagefi les(suchasAdobe?Photoshop?).

48-bitcapture

48-bitcapture

24-bittransfer

48-bittransfer

Imagequality Becausethescannercapturesdatathat nevercouldhavebeenreadbya24-bitor 30-bitscanner(suchasthedetailindark areasandslightcolortransitions),the scannerdeliversmoreaccurateimages

Witha48-bitimagefi le,youalwayshave accesstofullimagedata,whichisespeciallyimportanttographicartistsand designers.

Agreatercolorbitdepthgenerallyresultsinmoreaccuratecolorreproduction,smoothergradationswith fewersuddenshiftsincolor,anddetailedshadowsandhighlights.

ImageQuality--EpsonColorTrue?ImagingSystem

EpsonscannersusetheEpsonColorTrueIIImagingSystemwhichismadeupofthreemainelements (hardware,optics,andprocessing)andresultinsuperiorimagequalitywithfastprocessingspeeds.

Precisescancarriage SimultaneousRGBscanning

HighresolutionCCD Customglasslenses

Pixeloptimization CustomASIC

ScannerTechnicalBrief--Page3

6/07

ImageQuality--EpsonColorTrue?ImagingSystem(cont.)

Throughacombinationofthesehardware,optics,andprocessingfeatures,theEpsonColorTrueImaging SystemandEpsonColorTrueIIImagingSystemdeliverscannedimageswith:

Smoothgradations

Accuratecolors

Smoothedgesand minimalcolorfringing

Greaterdetailinshadows

Greaterdetailin highlights

Sharpimagequality withoutdistortion

1.Hardwarecomponents:Epsonscannersuseaprecisescancarriagewithbettermotorstoachievesubscan resolutionsthataredoubleorquadruplethescanner'sopticalresolution.Additionally,Epsonscanners captureRed,Green,andBluesimultaneously,versusotherscannersthatuseone-passscanningbut alternateRed,Green,andBluelightsforeachlineofascan.Epsonadvantagesare:

Bettercolorregistration Fasterscanningspeeds Higherqualitysub-scanresolutions

EpsonMethod (1/2or1/4stepcarriagemovement)

SimultaneousRGBCapture Onepass

Single-PassAlternateRGBMethod (1/2stepcarriagemovement)

RedCapture GreenCapture BlueCapture Onepass

2.Optics:EpsonscannersusecustomlensesthataredesignedspecificallytoworkwithEpsontechnology andthescanner'sCCD.Theselensesfeature:

Larger"sweetspot"andprecisionlensesforreduceddistortion Accuratelyalignedlenselementstocontrolsharpness Glasslenses(versusplasticlensesusedbymanycompetitors)

whichofferbetterreflectivequalities,providinggreaterimage quality. Betterimagequalitythancompetitiveoff-the-shelflenses becauseEpsonscannersfeaturecustom-madelensesthat matchtheCCD.

Small"sweetspot" canallowedge distortion

Larger"sweet spot"minimizes distortion

ScannerTechnicalBrief--Page4

6/07

ImageQuality--EpsonColorTrue?ImagingSystem(cont.)

3.Processing:ManyEpsonscannersuseacustomASIC(ApplicationSpecifi cIntegratedCircuit)forfast scanning.Keyfeaturesinclude:

LinecorrectioncapturesandprocessesfullRGBcolorforeverypixelandminimizescolorfringingin

subscandirection.

Zoomcapabilityenablessmoothestedgesalongdiagonalorcurvedlinesandachieveshigher

interpolatedresolution

On-boardmemoryallowsforAutoAreaSegmentation(AAS)andTextEnhancementTechnology(TET)

processingwithinthescanner--AASandTETareindependentfromPCorMacintoshprocessing,

allowingthescannertoworkwithbetter"raw"data.

Additionally,Epsonscannershaveapixeloptimizationfeature thatusesthefullresolutionofthescanner'sCCD,evenscanning

600dpi

EpsonMethod:

atalesserresolution.Thebenefi tofthisfeatureistruerimage quality.

300dpi

Forexample,ononeoftheEpson600dpiPerfection

Average Average Average

scanners,whenscanninganimageat300dpi,thescanner stillusesall600pixelsperinchtoscantheimage,then averagesthedatatoyieldthelowerresolutionimage.

CompetitiveMethod: 600dpi On Off On Off On Off

Somecompetitivemodelslowerresolutionbyturningoff

somepixelstocapturelessimagedata.

300dpi

ImageQuality--ColorCCD

AllEpsonscannersuseacolorCCDwhichusesasinglewhitelightsource,insteadofamonochromeCCD andthreelightsources.ThecolorCCDresultsinfasterscanningspeedsandtheabilitytoscanthreedimensionalobjectswithoutproducingcolor"ghosts."

KeyDifferences Howitworks

ColorCCD

Red,green,andbluearequicklycaptured inthecolorCCDilluminatedbyasingle lightsource.

Glass

MonochromeCCD threeseparatelampsarefi redforeachline ofascan,slowingthescanningspeed.

Glass

ColorCCD

Whitelight source

Resultwhen Singlelightsourceallowsprecise scanningthree- alignmentwhenscanningnon-flat dimensionalobjects surfaces

Monochrome CCD

Redlight source

Greenlight source

Bluelight source

Thethreelampscancausemisalignment whenrefl ectedfromnon-fl atsurfaces.

ScannerTechnicalBrief--Page5

6/07

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download