数字图像处理的基本概念.ppt

****************************Thesolidblackcurverepresentstheamountoflightbeingreflectedfromthefigureatthetop.Theredcurverepresentsthebrightnessesofthisfigureasitisusuallyperceived.Totheleftofthepointwherethefigurejuststartstogetlighterpeopleusuallyseeadarkbarthatisslightlydarkerthattheareatotheleftofit.Atthepointwherethebrightnessjuststopsincreasing,peopleusuallyperceiveabrightbar.Thisphenomenonwasdiscoveredbythefamousphysicist,ErnstMachanditisinhishonorthatthesedarkandbrightbarsarecalledMachBands.TheseMachBandscanbeexplainedbycenter-surroundreceptivefieldinteractionswhichisdiscussedelsewhereinthisbook.

Thereceptivefieldsarerepresentedasadisk(+)andannulus(-).Thecenterdiskisanexcitatoryareaandtheannulusaninhibitoryarea.Thereceptivefieldsintheuniformlywhiteanduniformlyblackareasreceiveaboutthesamestimulationintheirexcitatorycentersandinhibitorysurrounds.Thereforethecenterexcitationsareinbalancewiththesurroundinhibitions.ThereceptivefieldoverthebrightMachBandgivesastrongerresponseinthecenterbecausepartofthesurroundisinthedarkerarea.Thereforeitreceiveslessinhibitionfromthesurroundthandidthecenterattheextremeleftandrightends.Thereceptivefieldoverthedarkbandreceivesmoresurroundinhibitionbecausepartofthesurroundisinthebrighterarea.Therefore,theexcitatoryresponseislessandthisresultsinourseeingthattheareaasdarker.**Somepeopletendtoseeshorterwavelengthcolors(greens,blues,violets,etc)asfurtherwaythanequallybrightlongerwavelengthcolors(yellows,oranges,reds).Brightercolorstendtobeseenascloser.TakeanotherlookattheredandblueZsandseeifyouagreewiththeseobservations****************************2.1.3采样与量化参数的选择一