人眼視覺特性課件

要點(diǎn)：人眼視覺人眼非正常視覺人眼錯(cuò)覺人眼視覺特性人眼視覺感光細(xì)胞(photoreceptorcells)：

桿狀細(xì)胞(rod)：?jiǎn)紊挂曞F狀細(xì)胞(cone)：彩色視覺

紅(red)

綠(green)

藍(lán)(blue)PrimaryColor基色

Lightenterstheretinaonthesidecontainingtheopticnervesandtravelsthroughallthelayerbeforereachingthereceptors.RetinaThisanimatedcartoonillustrateshowlight(whitedot)enterstheretinaonthesidecontainingtheopticnervesandtravelsthroughalloftheretinallayersbeforefinallybeingabsorbedbythephotopigmentsintheoutersegmentsofthereceptors.Aneuralsignal(yellowdot)isgeneratedinthereceptorswhichthentravelsthroughtheneuronsofthevariousretinallayersandfinallytravelsoutthroughtheopticnerveuptothelateralgeniculatenucleus.Howlightenterstheretinaandistransmittedouttheopticnerve

ElectronMicrographofHumanVisualReceptorsWhenlookingatanobjectthatisfarawaythelensiskindofskinny.Whathappenswhenlookingatanearbyobject?RefractionWhenlookingatnearbyobjectsthelensgetsfatter,causingtheimageoftheobjecttobefocusedontotheretinainthefovea.Whatwouldhappenifthelensdidnotgetfatter?Bytheway,thetechnicaltermforthischangeinlensshapeisaccommodation.Wefrequentlycallitfocusing.Ifthelenscannotproperlyfocuslightontheretina,theimagewillfalleitherbehindorinfrontoftheretina.Canyouguesswhatwouldhappenifthelensistoofat?Ifyouguessedthatwhenthelensistoofatthatlightisfocussedinfrontoftheretina,youwereright.Istherearemedyforlensproblemsthatdonotallowlighttobeproperlyfocusedontheretina?Sure.Manypeoplewearcontactlensestohelpimagelightproperlyontotheretina.Anothersolutionisforapersontowearglasses.Thisplacesalensinfrontoftheeyenotonthecorneaasisthecasewithcontactlenses.Arecentsolutionistousealasertoreshapethecornea.thissolutionispossibleonlyinsomecases.Therearetwokindsofastigmatism:1.lenticularand2.corneal.Astigmatismoccurswhenthesurfaceofthecorneaorofthelensisnotperfectlysmooth.If,forexample,thereisasmallflatspotonyourcorneatheimageinacertaindirectiononyourretinawillnotbeinperfectfocus.Ifthefigureontherightwasconstructedwithalltheradiallinesofequalsharpnessandcontrastapersonwithoutastigmatismwouldseealltheseradiallinesasperfectlysharpandwiththesamecontrast.Thediagramontherighthasbeenfudgedto

illustratehowitmightappeartoapersonwithastigmatism.

Thisconditioncanbecorrectedwithacornealcontactlensorcylinderlensinapairofspectacles.AstigmatismContactLensesAverythinplasticlens,oftenflexible(softlenses)floatsonalayeroftearsonthecornealsurfaceoftheeye.Theselensescanbeofthepermanentvarietyordisposable.Thepermanentvarietyneedtobeproperlycleanedandcaredfor.ThedisposableareoftenworncontinuouslyandthethrownCornealContactLensawaywhenremoved.Notehowthebottomedgeofthelensisagainstthelowereyelid.Ifthewearerlooksdown,thelensispushedupalittle.This"trick"canbeusedtoprovidebifocalcontactlenses.Theselenseshavedifferentpowersinthecenterthanintheperiphery.Whenthewearerlooksdowntoreadthelensismovedtoanewpositiontofacilitateseeingsharplyatnormalreadingdistances.Ifthereisanirregularityonthecornea(astigmatism)itisautomaticallycorrectedbythecombinationofthetearlayerandthecontactlens.Acylinderlensisdifferentthanasphericallenswhichiswhatonenormallyseesinspectacles.Althoughacylindricalcomponentmybebuiltintothatwhichappearsspherical.Ascanbeseenintheleftdiagramacylinderlenshaspoweronlyinoneaxis.Intheleftitisthehorizontalaxis.Thislensdoesnotrefractlightintheverticaldirection.CylinderlensSpectralSensitivityCurvesofRods&ConesWhenyoufirstenteranextremelybrightenvironment,forexample,whenemergingfromadarkmovieshouseintoaverybrightsunlitareathemancarvingtheduckwouldappearlikethis.

Butinlessthanaminutehewillappearasseenbelow.

Intheleftphotothecontrastisverylow.

Belowthecontrastisnormal.Whenlightadaptedascenemightlooklikethis.DarkAdaptationForapproximatelythefirst10minutesinthedark,theconesrequirelesslighttoreachathresholdresponsethandotherods.Thereafter,therodsrequirelesslight.Thepointatwhichtherodsbecomemoresensitiveiscalledtherod-conebreak.DarkAdaptationFunctionp.18Thefollowingdemonstrationis

anexampleofhowtheworldappearstoapersonwitha

severetypeofcolorblindness,deuteranopia.

Seehowyouwoulddoinacolor

blindworld…

人眼視覺Colorvisiondefectscause

problemsintherealworld

Whichmeatisthemost

thoroughlycooked?Whichmeatisthemost

thoroughlycooked?Whichflaskcontainsalightpink

solution?

Whichflaskcontainsalightpink

solution?

Whichofthefollowingslides

containsapinkcell?

Whichofthefollowingslides

containsapinkcell?

Whichpicturecontainsared

crayon?

Whichpicturecontainsared

crayon?

Theuseofcolorsothatcolorblindpeople(and

everyoneelse)canseewhatyouarepresenting.

Red-greencolorblindnessiscommon--about

4-5%ofthepopulation.Inyourpresentations,

colorshouldbeusedwithcaretoensurethat

yourcolorblindcolleaguescansee.

Initsmostsevereforms,color

blindnessiscausedbytheabsenceof

oneoftheconevisualpigments.

Shownhere,thespectralsensitivities

oftheconepigmentsincolornormal

trichromatsarecomparedwiththose

ofacolorblindperson.Alsocompare

thespectrumasitappearstoacolor

normalpersonwiththeillustrationof

howitmightlooktoared-greencolorblindperson.

Thedifficultieswithcertaincolorscanbeillustratedona

colorwheel.Foraseverelyred-greencolorblindpersonthere

areonlytwohues,theonesacolornormalpersonseesasyellowandblue.Intermediatecolors,theonesseenasblueish-greenandmagenta,appeargray.

Cleargraphicsareveryimportantandoftenthesourceofthemostdifficulty;herearetwoexamplesshowingthedifferencebetweengoodandbaduseof

color.TheTrickistokeepbrightnessdifferenceslargeandtoavoidcolorcombinationsthatdonotcontrastwell.

Acomparisonofthetwocolorwheelsshowswhichcolorcombinationswouldbe

difficulttosee.Graphicscausethemostproblems,butthecolorscanbeeconomicallyillustratedastextexamples,below.Theright-handcolumnillustrates

howthelefthandcolumnmightlooktoacolorblindperson.

Someexamplesofcolorcombinationsthatareeasilyseenbyacolorblindperson

areshownbelow.Theseareillustratedastextexamplesbuttheseprinciplesare

mostimportanttokeepinmindwhenpreparingdrawings,graphs,andfigures.

cone狗是色盲？點(diǎn)擊圖片播放視頻眼見為實(shí)？馬赫帶效應(yīng)MachbandsBoyntonIllusionColorInfluencesDistancePerceptionRadiatingLinesTaketwopiecesofpaperandplacetheiredgesascloseaspossibletobothsidesofonereddiagonal.Notethattheredsquareinthemiddleisthesameasalltheothersquaresonthatdiagonal.Nowmoveyourpiecesofpapertoexposemainlytheredsquaresontheotherdiagonal.Onthisdiagonal

alltheredsquares,includingthecenterone,areagainthesamecolorred.Becausethecentersquareiscommontobothdiagonalsthisexerciseprovesthatalltheredsquaresinbothdiagonalsareexactlythesameredcolor.Yet,whenthepatternisseenasawhole,thetworeddiagonalsappeardifferentfromeachotherColorAssimilationHermannGridIllusion點(diǎn)擊圖片播放FLASHHering&PogendorfIllusions點(diǎn)擊圖片播放FLASHWhichlineislonger,theredoneorthegreenone?Usearulertofindout.Youwillprobablybesurprised.Horizontal-VerticalIllusion點(diǎn)擊圖片播放FLASHLookattheupperrightfigure.Thisexperimentworksbetterifyoucloseoneeye.Fixateontheblackdotinthecenterforabout10-15seconds.Paycloseattentiontowhatyousee.Nowdothesamethingwiththeupperleftfigure.Didyounoticeanydifference?IntheaccompanyingexplanationItellyouwhatmostpeopleseeandthereasonforit."Stabilization"CausesFadingThisiscalledaKanizsafigureafterthepersonwhoinventedit.Ifyoulookcarefullyyouwillprobablyseetheedgesoftheentiretriangle,eventhoughthetriangleisdefinedonlybythenotchesinthereddisks.KanizsaIllusionWhichislonger,theredlineortheblueline?Usearulertofindouttheanswer.Selecttheanswertodoublecheckonyourresult.Mueller-LyerIllusion點(diǎn)擊圖片播放FLASHTherounddotsareallexactlythesamecolorgray.Imerelycreatedtheoneontheextremerightandthencopiedittoeachofthedarkerrectangles.Clearly,thelightnessofthebackgroundeffectsthewayinwhichweperceivethecentergraydot.Thiseffectiscalledsimultaneouscontrast.Again,ascanbeseeninotherdemonstrations,theperceptionofthiskindofdisplayisaresultoflateralinteractions.SimultaneousContrastThecircularareaineachquadrantintheleftfigureisexactlythesamecolor.Thedifferentappearanceisduetothesurroundandthelateralinterac