基于TCS230颜色传感器的色彩识别器的设计 外文翻译

SensingcolorwiththeTAOSTCS230TheTAOSTCS230isasmall,highlyintegratedcolorsensingdevicepackagedinaclearplastic8-pinSOIC.Itreports,asanalogfrequency,theamountofshortwave(blue),mediumwave(green),longwave(red),andwideband(white)opticalpowerincidentontothedevice.Itcanbeusedinavarietyofcolorsensingapplications.Detailsofthedevicecanbefoundinitsdatasheet.ThiswhitepaperdetailstheconceptsandcalculationsinvolvedincolorsensingusingtheTCS230.WewillusetheColorCheckerchartasanopticalstimulustoworkthroughanumericalexampleofcolorsensing.Thechart,depictedinFigure1,ismanufacturedanddistributedbyGretagMacbeth.Thechartmeasuresapproximately13inchesby9inches(330mmby230mm);itcontains24coloredpatchesarrangedina6by4array.Figures2through5overleafshowthespectralreflectanceofthepatchesineachofthefourrowsofthechart–thatis,thefractionofincidentlightthatisreflected(withrespecttoanidealdiffusereflector),asafunctionofwavelengthfrom350nmto750nm.Figure1TheColorCheckercontains18coloredpatchesanda6-stepgrayseries.Figure2ColorCheckerspectra,toprow.Figure3ColorCheckerspectra,secondrow.Figure4ColorCheckerspectra,thirdrow.Figure5ColorCheckerspectra,bottomrow(neutralseries)Figure6Conesensitivitiesofconephotoreceptorsareshown.Theshortwave-sensitivephotoreceptorsaremuchlesssensitivethantheothertwotypes.Theresponsesofthemediumwaveandlongwavephotoreceptorshaveagreatdealofoverlap.Visionisnotsensitivetotheprecisewavelengthofthestimulus:Whatattersisopticalpowerintegratedundereachresponsecurve.IntroductiontocolorvisionPhotoreceptorcellscalledconesintheretinaareresponsibleforhumancolorvision.Therearethreetypesofconecells,sensitivetolongwave,mediumwave,andshortwaveradiationwithintheelectro-magneticspectrumbetweenabout400nmand700nm.Becausetheconesensitivitiesareveryroughlyinthepartsofthespectrumthatappearred,green,andblue,colorscientistsdenotethecelltypesasρ,γ,and,theGreeklettersforr,g,andb.(TodenotethesensorsR,G,andBwouldwronglysuggestaclosercorrespondence.)EstimatesofthespectralresponseoftheconetypesaregraphedinFigure6above.Lightinthephysicalworldcanbecharacterizedbyspectralpowerdistributions(SPDs).Coloredobjectscanbecharacterizedbyspectralreflectancecurves,suchasthoseoftheColorChecker.However,visionisinsensitivetotheexactwavelengthofastimulus:Accordingtothemoderntheoryofcolorscience,allthatmattersistheintegralofopticalpowerunderneatheachresponsecurve.Thatthereareexactlythreetypesofconecellsleadstothepropertyoftrichromaticity:Threecomponentsarenecessaryandsufficienttocharacterizecolor.Somepeoplemightusethephrase“colorassensedbytheeye,”butIcon-siderthatqualifiertoberedundantatbest,andmisleadingatworst:Colorisdefinedbyvision,sothereisnoneedtousethequalifyingphrase“assensedbytheeye,”ortousetheadjectivevisiblewhenreferringtocolor.OverviewofCIEColorimetryThespectralresponsesoftheconecellsthatIgraphedinFigure6wereunavailabletoresearchersinthe1920s.Researchersatthetimeusedpsychophysicalexperiments,suchasthefamouscolormatchingexperiment,toteaseoutthedata.TheCIEistheinternationalbodyresponsibleforcolorstandards.In1931,thatorganizationadoptedthecolormatchingfunctionsdenotedx(λ),y(λ),andz(λ),graphedinFigure7.Figure7CIE1931,2°color-matchingfunctions.Acamerawith3sensorsmusthavethesespectralresponsecurves,orlinearcombinationsofthem,inordertocaptureallcolors.However,practicalconsiderationsmakethisdifficult.Theseanalysisfunctionsarenotcomparabletospectralpowerdistributions!WeightingaphysicalSPDundereachofthesethreecurves(thatis,formingthewavelength-by-wavelengthproduct),andsummingtheresults,formsatripleofthreenumbers,denotedX,Y,andZ.Incontinuousmathematics,threeintegralsneedtobecomputed;indiscretemath,amatrixproductissufficient.TheX,Y,andZtristim-ulusvaluescharacterizecolor.Theyarelinear-lightquantities,propor-tionaltoopticalpower,thatincorporatethewavelengthsensitivityofhumanvision.TheYvalueisluminance,whichisordinarilyexpressedinunitsofcandelapermetersquared(cd·m-2).Ifyouaremeasuringreflectance,thereflectedtristimulusvaluesdependuponthespectralcharacteristicsoftheilluminant,andtheiramplitudesscalewiththepoweroftheillumination.Relativeluminanceistheratioofreflectedluminancetotheluminanceoftheillumination;itisalsoknownastheluminancefactor.Figure8SPDsofvariousilluminantsaregraphedhere.IlluminantA,showninorange,isrepresentativeoftungstenlightsources;itisdeficientinshortwavepower,andmaycauseerrorsinsensingbluecolors.ThebluelinegraphstheSPDofaNichiawhiteLED.Thereisapeakintheblueportionofthespectrum:Uncorrected,thesensorwouldreportexcessivebluevalues.TheotherfourlinesrepresentCIEstandardilluminantsC,D50,D55,andD65.Inmanyapplications,tristimulussignals(includingluminance)scalewiththeillumination,andareotherwiseuninterestinginthemselves.Whatismoreinterestingistheratiosamongthem,whichcharacterizecolordisregardingluminance.TheCIEhasstandardizedtheprojectivetransformationofEquation1,inthemargin,totransform[X,Y,Z]valuesintoapairof[x,y]chromaticitycoordinatesthatrepresentcolordisregardingluminance.Thesecoordinatesaresuitableforplottingintwodimensionsonachromaticitydiagram.x=𝑋/(𝑋+𝑌+𝑍