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.

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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.

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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.

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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.

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ThesphereontherighthashadtheSamplingparametersaddedandthevaluesadjustedtoremoveanynoise.TherestoftheobjectsinthesceneusethesamplingvaluessetontheMantranode.(Forthepurposesofthisexample,NoiseLevel:0.01,MinRays1,MaxRays2).

Youcanseethatmantrasamplestheobjectsinthescenesatdifferentrates,allowingyoutooptimizetherenderingofspecificobjectsinyourscenewithoutnegativelyaffectingtheoverallsamplingofyourimage.