H16MantraUserGuide
REMOVINGNOISEAsdescribedintheSamplingsection,under-samplingisalmostalwaysthecauseofnoiseinyourrenders.Simplyincreasingtheoverallamountofsamplingwillreducetheamountofnoise,butitwillalsocausemanypartsofyourimagetobeover-sampledandyourrendertimestoincrease.Targetingthevarioustypesofraystothecorrectpartofyourimageiscriticalforoptimization,sendingmoreofthewrongkindofraywillnotincreasethequalityofyourrender.Thegoal,whensettingyoursamplingparameters,istobalanceSpeedwithQuality.Formoreinformationaboutthespecificparametersdescribedbelow,seeTheSamplingTabandtheExtraImagePlanesTab.
Ingeneral,whenattemptingtoremovethenoiseinyourrender,itisgoodpracticetostartbyaddingthefollowingimageplanes:
DirectLighting(percomponent)
IndirectLighting(percomponent)
DirectSamples
IndirectSamples
Thesewillallowyoutoanalyzedifferentpartsofyoursceneoneatatime.
Thefollowingrenderisanexampleofascenewithmultiplematerialtypesandmotionblur.AllsamplingvaluesontheMantraNodearesettothedefaultsexceptforPixelSamples,whichare1x1.Onthelimitstab,DiffuseLimithasbeensetto2,VolumeLimithasbeensetto2andSSSlimithasbeensetto1.
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ForeachExamplebelow,wewilladjustonlytheparametersthatarementionedinthedescriptionsaccompanyingeachnoisetype.
MotionBlurWhen“AllowMotionBlur”isenabledontheMantranode,fastmovingobjectscancauseyourimagetobecomenoisy.Thisnoiseisessentiallyatypeofaliasingthatoccurswhenanobjectmustbesampledacrosstimeaswellasspace.SeethechapteronMotionBlur,foramoreindepthexplanationofhowmantrasamplesobjectsinmotionandhowcertainobjectsmaybeoptimizedforheavilymotionblurredscenes.
IncreasingPixelSamples,alsodescribedasPrimaryRays,istheonlywaytoremovethistypeofnoise.
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IncreasingPixelSampleswillactasamultiplierforallothertypesofrays(seeSamplingTab).Intheexampleabove,youcanseethatincreasingthepixelsampleshasalsoremovedmostoftheothertypesofnoiseinthisscene.Forthisreason,itisagoodideatoremoveMotionBlurasafirststepasitmaysolveothertypesofnoiseinyoursceneatthesametime.
Toidentifythistypeofnoise,itcanbeusefultochecktheAlphaChannelfornoiseattheendsofobjects.Ifoverlappingobjectsmakethisimpossible,turnoff“AllowMotionBlur”andcheckthenoiselevelsversusthenon-motionblurredscene.
DepthofFieldWhen“EnableDepthofField”ischeckedontheMantraNode,objectswhicharedistantfromthecamera’s“FocusDistance”canbecomenoisy.Thisisespeciallyevidentinbrighthighlightsandtheedgesofobjects.
IncreasingPixelSamplesistheonlywaytoremovethistypeofnoise.
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AswithMotionBlur,removingnoisefromimageswithDepthofFieldmayhavethesideeffectofremovingothertypesofnoiseaswell.Considerremovingthistypeofnoisefirstbeforeattemptingtoremovenoisefromothersources.However,alwayscheckthe“infocus”areasofyourimageforanyoftheothernoisetypesassomeextraattentionmayberequiredintheseareas.
Toidentifythistypeofnoise,itcanbeusefultochecktheAlphaChannelfornoiseattheedgesofobjectsoralongthemotionpath.Ifoverlappingobjectsmakethisimpossible,turnoff“EnableDepthofField”andchecktheamountofnoiseintheimagewithoutDepthofFieldblurring.
EdgeAliasing
WithoutenoughPrimaryRays,theedgesofobjectscanappearjaggedandrough.Thiscanbeespeciallyevidentinhigh-contrastareasorwithinhigh-frequencypatterns.
IncreasingPixelSamplesistheonlywaytoremovethistypeofnoise.
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Intheaboveexample,noticehowtheedgesofthesphereandplaneappearjaggedintheimageontheleft.
Toidentifythistypeofnoise,itcanbeusefultochecktheAlphaChannelfornoiseattheedgesofobjectsoralongthemotionpath.
Formanyscenes,settingpixelsamplesto3x3willbesufficienttoremovethistypeofnoise.Forimageswithhighfrequencypatternsgeneratedbyashader,itmaybenecessarytoincreasethesevaluestogetafullyanti-aliasedimage.Ifpossible,itmaybemoreefficienttohandlefilteringintheshader,ratherthatusingthebruteforceapproachofincreasingpixelsamples.
H16MantraUserGuide
DIRECTILLUMINATIONDirectReflectionsDirectReflectionsrefertothereflectionoflightsourcesdirectlyfromthesurfaceofanobject.ThesereflectionscanexhibitaspecklednoisepatternespeciallyinmaterialswithsmallamountsofroughnessincombinationwithAreaLightsorEnvironmentLights.
ThebestwaytoremovethistypeofnoiseistoincreasetheSamplingamountontheLightwhichiscausingthenoise.IncreasingPixelSampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays.ItcanoftenbeagoodideatostartwiththedefaultPixelSamplevalueof3x3becauseitwillalsoremoveanydistractingEdgeAliasingfromyourimage.
IncreasinglightsampleswillactlikeamultiplieronthenumberofDirectRaysinyourscenesoitisnotagoodideatosimplyincreasesamplestoextremelyhighvaluesforalllights.IncreasingDirectrays(MinandMaxRaySamples)willhelpremovethistypeofnoise.Thismeansthatyoumustbalancetheneedtocleanupnoisefromaspecificlight,againstcleaningupDirectSourcesofnoisethroughoutyourimage.
Toidentifythistypeofnoise,enablethe“DirectReflect”imagelayer,thiswillallowyoutoexaminethecontributionstoDirectReflectionswithoutinterferencefromothersourcesofnoiseinyourscene.
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Intheaboveimages,theDirectReflectionnoiseismuchclearersinceitnolongermixedinwithallothersourcesofnoise.
Forcomplexsceneswithmanylights,itcanbeusefultoexportthe“DirectReflect”layerusingthe“PerLight”option.Thiswillallowyoutoisolatethespecificlightsthatarecausingnoiseinyourscene,allowingyoutoincreasesamplingonlyontheoffendinglightsources.
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DirectRefractionsDirectRefractionsarecausedbytherefractionoflightsourcesthroughasinglesurface(Agridforinstance)TheserefractionscanexhibitaspecklednoisepatternespeciallyinmaterialswithsmallamountsofroughnessincombinationwithAreaLightsorEnvironmentLights.
(RememberthatanyrefractionsthroughmorethanonesurfacewillbeconsideredanIndirectRefraction.)
ThebestwaytoremovethistypeofnoiseistoincreasetheSamplingamountontheLightwhichiscausingthenoise.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
Intheaboveexample,increasingthePixelSamplesto3x3removesalltheDirectRefractionnoiseandsotheSamplingQualityontheEnvironmentLightdidnotneedtobeadjusted.Thisisanothergoodreasontoapproachtheremovalofnoiseinstages.Forthiscase,RemovingEdgeAliasinghaseffectivelyresolvedtheDirectRefractionnoiseaswell.
IncreasinglightsampleswillactlikeamultiplieronthenumberofDirectRaysinyourscenesoitisnotagoodideatosimplyincreasesamplestoextremelyhighvaluesforalllights.Also,increasingDirectrays(MinandMaxRaySamples)willalsohelpcleanupthistypeofnoise.Thismeansthatyoumustbalancetheneedtocleanupnoisefromaspecificlight,againstcleaningupDirectSourcesofnoisethroughoutyourimage.
Toidentifythistypeofnoise,enablethe“DirectRefract”imagelayer,thiswillallowyoutoexaminethecontributionstoDirectRefractionswithoutinterferencefromothersourcesofnoiseinyourscene.
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Forcomplexsceneswithmanylights,itcanbeusefultoexportthe“DirectRefract”layerusingthe“PerLight”option.Thiswillallowyoutoisolatethespecificlightsthatarecausingnoiseinyourscene,allowingyoutoincreasesamplingonlyontheoffendinglightsources
DirectShadowsDirectShadows,whichoccurwhenapointinyourscenedoesnothaveadirectpathtoalightsource,canexhibitaspeckledorroughnoisepattern.Thisisespeciallyevidentinsoftshadowscastfromlargearealights.
ThebestwaytoremovethistypeofnoiseistoincreasetheSamplingamountonthelightwhichiscausingthenoise.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
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Increasinglightsampleswillactlikeamultiplieronthenumberofdirectraysinyourscenesoitisnotagoodideatosimplyincreasesamplestoextremelyhighvaluesforalllights.Also,increasingDirectrays(MinandMaxRaySamples)willalsohelpcleanupthistypeofnoise.Thismeansthatyoumustbalancetheneedtocleanupnoisefromaspecificlight,againstcleaningupDirectSourcesofnoisethroughoutyourimage.
Toidentifythistypeofnoise,enablethe“DirectDiffuse”imagelayer,thiswillallowyoutoexaminetheshadowscausedbydirectlightingwithoutinterferencefromindirectsourcesofshadow.
Intheaboveexample,identifyingwhichlightisresponsibleforthenoiseisdifficult,especiallysinceenvironmentlightshavetheeffectof“fillingin”shadows.Itcanbeusefulinthesecasestoexportthe“DirectDiffuse”layerusingthe“PerLight”option.Thiswillallowyouisolatethespecificlightsthatarecausingnoiseinyourscene,allowingyoutoincreasesamplingonlyontheoffendinglightsources.
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Intheexamplesabove,itismuchmoreobviouswhichlightiscausingthevarioustypesofnoise.Thisisespeciallyevidentontheedgesoftheshadowscastbythearealight.Inthiscase,youcanseethattheArealightrequiredfewersamplestoremovethenoisethantheEnvironmentlight.Incomplexscenes,thiskindofcloseexaminationofper-lightnoisecanhelppreventsignificantlyover-samplingyourscene.
H16MantraUserGuide
INDIRECTILLUMINATIONIndirectDiffuse
IndirectDiffuse,whichisthelightcontributionfromotherobjectsinascene,canbeasignificantsourceofnoise.Thiscanbeespeciallyevidentinsceneswithphysicallyaccuratelightsourceswhicharealsoverynearotherobjects(Lightsconcesorinsetlights,forinstance.)andonlycontributeasmallamounttodirectlighting.
Thebestwaytoremovethistypeofnoiseistoincreasethenumberofindirectsamplesthatarebeingsent.YoucanachievethisbyadjustingtheDiffuseQualityparameterontheMantranode.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
Toidentifythistypeofnoise,enablethe“IndirectDiffuse”imagelayer,thiswillallowyoutoexaminethelightcontributionstothislayerwithoutinterferencefromothertypesofnoise.
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Keepinmindthatyoudonothavetocompletelyremovenoisefromthiscomponenttohaveacleanimage,indirectnoiseisoftenimperceptiblewhenithasbeencombinedwithdirectlightinginformation.AlwaysrefertotheCombinedColorimageplanetoseehowyoursamplingisaffectingthefidelityofthefinalimage.
IndirectReflections
IndirectReflections,whicharethereflectionsofotherobjects,canberesponsibleformuchofthenoiseinyourscene.Thiscanbeparticularlyevidentinsceneswithverybrightglossyreflectionsincombinationwithotherobjectswithroughreflections.
Thebestwaytoremovethistypeofnoiseistoincreasethenumberofindirectsamplesthatarebeingsent.YoucanachievethisbyadjustingtheReflectionQualityparameterontheMantranode.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
Toidentifythistypeofnoise,enablethe“IndirectReflect”imagelayer,thiswillallowyoutoexaminetheamountofnoisecausedbyindirectreflectionswithoutinterferencefromothertypesofnoise.
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Keepinmindthatyoudonothavetocompletelyremovenoisefromthiscomponenttohaveacleanimage,indirectnoiseisoftenimperceptiblewhenithasbeencombinedwithdirectlightinginformation.However,unlikeindirectdiffusenoise,indirectreflectionscanberesponsibleformostofthecolorofafinalpixel.(Anobjectwithamirror-likefinish,forexample)AlwaysrefertotheCombinedColorimageplanetoseehowyoursamplingisaffectingthefidelityofthefinalimage.
IndirectRefractions
IndirectRefractions,whicharetherefractionsofotherobjectsandsurfacesinyourscene,canbesignificantsourcesofnoiseinyourscene.Thisisespeciallytruewhenrenderingrefractiveobjectswithahighroughnessvalue.
Thebestwaytoremovethistypeofnoiseistoincreasethenumberofindirectsamplesthatarebeingsent.YoucanachievethisbyadjustingtheRefractionQualityparameterontheMantranode.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
Toidentifythistypeofnoise,enablethe“IndirectRefract”imagelayer,thiswillallowyoutoexaminetheamountofnoisecausedbyindirectrefractionswithoutinterferencefromothertypesofnoise.
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Keepinmindthatyoudonothavetocompletelyremovenoisefromthiscomponenttohaveacleanimage,indirectnoiseisoftenimperceptiblewhenithasbeencombinedwithdirectlightinginformation.However,unlikeindirectdiffusenoise,indirectrefractionscanberesponsibleformostofthecolorofafinalpixel.(Aglassofwater,forinstance.)AlwaysrefertotheCombinedColorimageplanetoseehowyoursamplingisaffectingthefidelityofthefinalimage.
SubsurfaceScattering
SubsurfaceScatteringreferstoatypeofindirectlightcausedbylightscatteringinsidethesurfaceofanobjectbeforeexiting.Typically,thiseffectisseeninmaterialslikecandlewaxorhumanskin.ObjectswithSubSurfaceScatteringenabledcancontributeasignificantamountofnoiseinyourscene.
Toremovethistypeofnoise,increasetheSSSQualityparameterontheMantranode.IncreasingPixelsampleswillalsohelpremovethenoise,butwillcauseanincreaseinallothertypesofrays,causingareasoftheimagewithoutnoisetobecomeover-sampled.
Toidentifythistypeofnoise,enablethe“IndirectSSS”imagelayer,thiswillallowyoutoexaminetheamountofnoisecausedbyindirectreflectionswithoutinterferencefromothertypesofnoise
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Keepinmindthatyoudonothavetocompletelyremovenoisefromthiscomponenttohaveacleanimage,SSSnoiseisoftenimperceptiblewhencombinedwithotherlightingcomponents.However,insomematerialstheSSScomponentmayberesponsibleformuchofthefinalpixelcolor,inthosecasesasignificantincreaseinthenumberofrayssentmaybenecessary.Additionally,becauseSubsurfaceScatteringishighlydependingontheviewingangle,itmaybeagoodideatotestyoursamplingsettingsacrossmultipleframesifyourcameraorobjectisanimated.AlwaysrefertotheCombinedColorimageplanetoseehowyoursamplingisaffectingthefidelityofthefinalimage.
VOLUMES
Volumesrequireadifferentsamplingstrategythansurfaces,rays“march”througheachobjectandaccumulatevaluesacrossmultipledepthsamples.Thisaddedcomplexitycanmakerenderingvolumescostly.Likesurfaces,itisbesttoapproachtheremovalofnoiseinaseriesofstagesbasedonthetypeofnoisepresent.DirectVolumesDirectVolumetriclighting,referstovolumesthathavereceivetheirlightingonlydirectlyfromlightsources.
Whenrenderingvolumes,therecanbemorethanonetypeofnoisepresentpercomponent-noisefromunder-samplingthetransparentpartsofanobjectandnoisefromunder-samplingthelights.
Tobegin,increasingStochasticSampleswilldramaticallyreducenoisewithoutcausingalargeincreaseinrendertimes.Thiswillbemostnotableinsemi-transparentareas,usuallyinthesoftedgesofthevolumetricobject.Atsomepoint,increasingStochasticSampleswillnolongerhaveasignificanteffectonnoise.Ifthisoccurs,andnoiseremainsinthiscomponent,beginincreasingMaxRaySamplesslowlyuntiltheremainingnoiseisremoved.
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Toidentifythesetypesofnoise,enablethe“DirectVolume”imagelayer,thiswillallowyoutoexaminetheamountofnoiseinthiscomponentwithoutinterferencefromtypesofnoise.
Aswithallnoisetypes,increasingPixelsampleswillhelpreducethistypeofnoise.Thiscanbeparticularlyexpensivewhenrenderingvolumes,soitisbesttoavoidthisifpossible.However,thedefaultsettingof3x3pixelsamplesisoftenagoodstartingplace.
Ifyouplantocompositeyourvolumetricimageswithaseparatebackgroundimage,besuretooccasionallycheckthenoiselevelsaftercompositing.Noisethatisevidentagainstablackbackgroundmaybeinvisibleonyourfinalplate.Theoppositecanalsobetrue,wherenoiseisinvisibleagainstablackbackground,butbecomesobviouswhenthealphachanneloftheimageistakenintoaccount.Asmuchaspossible,refertotheCombinedColorchannel(orthecompositedfinalframe)toverifyhowyoursamplingisaffectingthefidelityofyourimage.
IndirectVolumetricLightingIndirectVolumetricLighting,whichinvolvesvolumeswhichreceivelightfromindirectsourcessuchasotherobjectsorthroughthescatteringoflightwithinthevolumeitself,cancreatesignificantamountsofnoiseinyourrenders.Indirectvolumetricnoiseismostoftennoticeableintheshadowedareasofvolumetricobjects.
H16MantraUserGuide
AswithDirectVolumenoise,beginbyremovingthenoisecausedbyunder-samplingtheopacityofyourvolumebyincreasingStochasticSamples.However,ifyou’vealreadyremovedthistypeofnoisefromyourdirectvolumecomponent,youmayfindthatincreasingthevalueofthisparameterhaslittleeffectsincetransparentsamplesaresharedbetweenthesecomponents.
Theremainingnoiseislikelyduetounder-samplingtheindirectsourcesoflightinyourscene.Toremovethisnoisetype,slowlyincreasetheMaxRaySamplesparameteruntilthenoiseisresolved.LikeStochasticsampling,thisparameterissharedwiththedirectvolumecomponent.However,becauseindirectsamplingofvolumescanbeespeciallynoisy,itislikelyyouwillneedtoincreasethemaxraysamplesfurthertoremovenoisefromthiscomponent.
Toidentifythistypeofnoise,enablethe“IndirectVolume”imagelayer,thiswillallowyoutoexaminetheamountofnoisecausedbyindirectvolumetriclightingwithoutinterferencefromtypesofnoise.
Keepinmindthatyoudonothavetocompletelyremovenoisefromthiscomponenttohaveacleanimage,oftenindirectnoiseisinvisiblewhenithasbeencombinedwithdirectlightinginformation.AlwaysrefertotheCombinedColorimageplanetoseehowyoursamplingisaffectingthefidelityofthefinalimage.
VolumeQualityUnliketheother“Quality”parametersontheSamplingTaboftheMantraNode,VolumeQualitydoesnotrefertotheamountofindirectsampling.Instead,itexplicitlyreferstothenumberofvoxelswhichareconsideredforsampling.(See“TheSamplingtab”formoreinformationonthisparameter)
Ingeneral,itwillbeunnecessarytochangethisparametersolongasStochasticTransparencyinenabled.However,itispossiblethatsmalldetailswillbemissedwhenthisVolumeQualityissettoolow.
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Ifyoufeelthatthereismoreinformationinthevolumethanappearsintherender,considerincreasingthisvalue.
WhenStochasticTransparencyisdisabled,thisparameterdirectlycontrolstheamountofsamplinginthevolumeandwillhaveadramaticeffectonrendertimes.
FINALIMAGEHereisaversionofthecompletescenewiththerenderingsettingsrequiredtogenerateacleanimage.
SPECIALCASESInsomecases,theremaybespecificobjectsinyourscenethatareespeciallynoisyincomparisontootherobjects.Youmayfindthattogetenoughsamplesontotheseobjectsyouwillendupover-samplingtherestofyourscene.Thiscanoccurinmanydifferentcircumstances,butacommoncausewouldbearefractiveorreflectiveshaderwithhighroughnessvalues.
H16MantraUserGuide
Toavoidthisover-samplingproblem,youcanaddthesamplingpropertiesontotheobjectitself.Thiswillmeanthatonlytheproblem-casewillreceivemoresamples.Toachievethis,gotoanobjectandselectthe“EditRenderingParameters”optioninthegearicon.
Under“RenderProperties”,navigatetotheMantra/Samplingfolder(OrusetheFilterFieldtonarrowyoursearch).Addthefollowingpropertiestoyourobject:–
DiffuseQuality
ReflectionQuality
RefractionQuality
SSSQuality
MaxRaySamples
MinRaySamples
NoiseLevel
ThesepropertieswillgiveyouthesamecontroloversamplingthatyouhaveontheMantranode,butisolatedtothisspecificobject.NotethatPixelSamplescannotbealteredperobject,itisaglobalsetting.
H16MantraUserGuide
ThesphereontherighthashadtheSamplingparametersaddedandthevaluesadjustedtoremoveanynoise.TherestoftheobjectsinthesceneusethesamplingvaluessetontheMantranode.(Forthepurposesofthisexample,NoiseLevel:0.01,MinRays1,MaxRays2).
Youcanseethatmantrasamplestheobjectsinthescenesatdifferentrates,allowingyoutooptimizetherenderingofspecificobjectsinyourscenewithoutnegativelyaffectingtheoverallsamplingofyourimage.