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Pixel Size. A pixel is the part of a sensor which collects photons so they can be converted into photoelectrons. Multiple pixels cover the surface of the ... PixelSizeandCameraResolutionEducationalNotes PixelSize Apixelisthepartofasensorwhichcollectsphotonssotheycanbeconvertedintophotoelectrons.Multiplepixelscoverthesurfaceofthesensorsothatboththenumberofphotonsdetected,andthelocationofthesephotonscanbedetermined. Pixelscomeinmanydifferentsizes,eachhavingtheiradvantagesanddisadvantages.Largerpixelsareabletocollectmorephotons,duetotheirincreaseinsurfacearea.Thisallowsmorephotonstobeconvertedintophotoelectrons,increasingthesensitivityofthesensor.However,thisisatthecostofresolution. Smallerpixelsareabletoprovidehigherspatialresolutionbutcapturelessphotonsperpixel.Totryandovercomethis,sensorscanbeback-illuminatedtomaximizetheamountoflightbeingcapturedandconvertedbyeachpixel.  Thesizeofthepixelalsodeterminestheoverallsizeofthesensor.Forexample,asensorwhichhas1024x1024pixels,eachwitha169μm2surfacearea,resultsinasensorsizeof13.3x13.3mm.Yet,asensorwiththesamenumberofpixels,nowwitha42.25μm2surfacearea,resultsinasensorsizeof6.7x6.7mm. CameraResolution Cameraresolutionistheabilityoftheimagingdevicetoresolvetwopointthatareclosetogether.Thehighertheresolution,thesmallerthedetailthatcanberesolvedfromanobject.Itisinfluencedbypixelsize,magnification,cameraopticsandtheNyquistlimit.Cameraresolutioncanbedeterminedbytheequation: CameraResolution= ( PixelSize Magnification ) * 2.3 Where2.3compensatesfortheNyquistlimit.ThislimitisdeterminedbytheRayleighCriterionofthesample.TheRayleighCriterionisdefinedbywhetherornottwoneighboringAirydisks(centralbrightspotofthediffractionpatternfromalightsource)canbedistinguishedfromoneanother,determiningthesmallestpointthatcanberesolved(asshowninFigure1). Figure1:Left:TwoneighboringAirydisksthatcanbedistinguishedfromeachother.Right:TwonieghboringAirydisksthatcannotbedistinguishedfromeachotherastheyarebelowtheRayleighCriterion. Nyquistlimitdetermineswhetherasensorcandifferentiatebetweentwoneighboringobjects.IfthedistancebetweentwoobjectsisgreaterthantheNyquistlimit,orexceedthislimitbyafactorofatleast2,asensorcandistinguishbetweenthetwoobjects.TheNyquistlimitisdeterminedbythespatialfrequency(numberofbrightspotswithinagivendistance)oftheobjectyouaretryingtoimage. Forexample,ifyouaretryingtomeasureafewbrightspotsthatareαnmapart,youwillneedtomeasureatleastevery nmtocapturethespatialfrequency(i.e.resolvethebrightspots).Thisspatialfrequencyallowsthegapsbetweenthebrightspotstobecapturedasablackpixel(i.e.apixelwithoutsignal).Ifthedistancebetweenthebrightspotsisgreaterthanthesizeofthepixel,ablackpixelwillnotbecapturedandthereforethebrightspotswillnotberesolved.Thisiswhysmallerpixelsprovidehigherresolution,asshowninFigure2. Figure2:SchematicshowingthatthereneedstobeatlestonepixelwidthbetweentwoobjectsfortheNyquistlimittobeovercome,allowingthetwoobjectstoberesolved.Thisiswhysmallerpixelsprovidehigherresolutionastheyareabletodistinguishbetweensmallerobjects. LensResolution Itisalsoimportanttoconsidertheresolutionofthecameralenswhendeterminingtheoverallsystemresolution.Theabilityforalenstoresolveanobjectislimitedbydiffraction.Whenthelightemittedfromanobjecttravelsthroughalensapertureitdiffracts,formingadiffractionpatternintheimage(asshowninFigure3A).ThisisknownasanAirypattern,andhasacentralspotsurroundedbybrightringswithdarkerregionsin-between(Figure3B).ThecentralbrightspotiscalledanAirydisk,ofwhichtheangularradiusisgivenby: θ= 1.22 λ D Whereθ istheangularresolution(radians),λisthewavelengthoflight(m),andDisthediameterofthelens(m). TwodifferentpointsonanobjectbeingimagedproducetwodifferentAirypatterns.IftheangularseparationbetweenthetwopointsisgreaterthantheangularradiusoftheirAirydisk,thetwoobjectscanberesolved(Rayleigh’sCriterion).Iftheangularseparationissmaller,however,thetwodistinctpointsontheobjectmerge.ThiscanbeseeninFigure3C. Figure3:(A)Depictionofadiffractionpatternproducedwhenalightsourcepassesthroughalensaperture.(B)AnexampleofanAirypatterndeterminedbylightdiffractedthroughanaperture.(C)Top:TwoneighboringAirypatternsthatcanbedistinguishedfromeachotherduetotheseparationoftheAirydisks.Middle:TwomergingAirydisks,preventingthemfrombeingdistinguished.Bottom:TwoneighboringAirypatternsfullymerged. TheangularradiusoftheAirydiskisdeterminedbytheapertureofthelens;therefore,thediameterofthelensaperturealsodeterminesresolution.AsthediameterofthelensapertureandtheangularradiusoftheAirydiskhaveaninverserelationship,thelargertheaperturethesmallertheangularradius.ThismeansthatalargerapertureresultsinhigherlensresolutionasthedistancebetweensmallerdetailscanremaingreaterthantheangularradiusoftheAirydisk.Thisisoftenwhyastronomicaltelescopeshavelargelensdiameterstobeabletoresolvethefinerdetailsinstars. Summary Pixelscomeinvarioussizesdependingonwhatisrequiredfortheapplication.Alargepixelsizeisoptimalforlowlightimagingconditionsthatarelessconcernedwithhighresolution.Incomparison,asmallerpixelsizeisoptimalforbrightimagingconditionsinwhichresolvingfinedetailisoftheutmostimportance. Thesizeofthepixelalsodeterminesthenumberofpixelsonasensor,withafixedsensorsizehavingmorepixelsonthesurfacewithsmallerpixelsurfacearea. Cameraresolutionisdeterminedbythepixelsize,lensaperture,magnificationandNyquistlimit.OvercomingtheNyquistlimitisdowntothepixelsize,withsmallerpixelsallowingforevensmallerdetailstoberesolved.Thisisbecausethedistancebetweentwoneighboringobjectsneedstobebiggerthanthatofonepixelsize,allowingforablackpixeltobecaptureddistinguishingagapbetweenthetwoobjects. Lensresolutionislimitedbydiffraction.Airypatternsareformedwhenlightfromanobjectdiffractsthroughalensaperture.TheseAirypatternshavebrightcentralspotscalledAirydisks,whichhaveanangularradiusdeterminedbythelensaperturediameter.TwoneighboringobjectscanberesolvediftheangularseparationbetweentheobjectsisgreaterthantheangularradiusoftheAirydisk.Asthisisinverselyrelatedtotheaperturediameter,alargerlensapertureresultsinhigherresolution. Bothpixelsizeandlensaperturediameterneedtobetakenintoconsiderationwhenchoosingtherightcameraforaresearchapplication.  FurtherReadingFieldOfViewFieldofviewisthemaximumareaofasamplethatacameracanimage,andisdeterminedbythefocallengthofthecameralensandthesizeofthesensor. FindOutMoreCameraGainThegainrelatesthenumberofphotoelectronsreleasedtothegraylevelsdisplayed,andcanbeusedtoenhancecontrastforlow-lightimaging. FindOutMoreEnhancingUVSensitivityfrom10–400nmTherearemanysubcategoriesofUVlight,eachwhichneeddifferentsensorrequirements.Theseincludebothphysicalandchemicalsensorchanges. FindOutMore Thiswebsiteusescookies.Byproceedingnavigationonthispage,youagreetotheuseofcookiesaccordingtothetermsofourPrivacyPolicy. IAgree