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Hardware Accelerated Real Time Charcoal Rendering

Aditi Majumder M. GopiDepartmentof ComputerScience InformationandComputerScience

Universityof North Carolinaat ChapelHill Universityof California,[email protected] [email protected]

Abstract

In this paper, we presentsimplerenderingtechniquesimplementedusingtraditionalgraphicshardwareto achieve the effectsof char-coaldrawing. Theeffectsincludecharacteristicsof charcoaldraw-ings like broadgrainy strokesandsmoothtonalvariationsthatareachievedby smudgingthecharcoalby hand.Further, we alsogen-eratetheclosure effect that is usedby artistsat timesto avoid hardsilhouetteedges.All theseeffectsareachieved usingcontrast en-hancementoperators on texturesand/orcolorsof the3D model.

Our contribution lies in unifying the methodsto achieve theseeffectsunderthecommonframework of contrastenhancementop-erators.Further, sincetheeffectshavebeenimplementedusingtra-ditional graphicshardware,a singlerenderingpassis sufficient tocreatedifferenteffects.Hence,wecanrenderhighly complex mod-els with large numberof trianglesat interactive rates. Thus, ourmethodis especiallysuitedfor applicationslike scientific visual-izationandpreliminarysketches/animations.

CR Categories: 1.3.5[Non PhotorealisticRendering]:HardwareAcceleratedRendering—CharcoalRendering

Keywords: Non PhotorealisticRendering,HardwareAcceleratedRendering,Realtime rendering,CharcoalRendering

1 Introduction

In many applications– from medicaltexts to architecturaldesignandmechanicalillustrations– non-photorealisticrenderingis oftenmoreeffective thanphotorealism.Suchillustrationsperformanab-stractionon theactualscenecontentandconvey informationthatismostimportantto anobserver. Further, recentresearchhasshownthatsuchillustrationscanbeeasilyproduced,consumelessstorageandthuscanbea betterchoicethanphotorealismin many applica-tions.

Researchin non-photorealisticrendering(NPR)hasfoundmeth-odsto simulatetheeffectsof varioustraditionalmedialikepenandink [4, 27, 28,34, 35, 19], pencilsketches[1], watercolor [3] andengraving [21, 30]. Therehasbeenwork on renderingdifferentstyleslike impressionism[8, 10,15,18] andtechnicalillustrations[6, 26, 25]. Therehasalsobeenwork onnon-photorealisticrender-ing of specificobjectslike fur andgrass[13, 14]

To thebestof our knowledge,exceptfor an interactive 2D sys-temdevelopedin 1988[2], we have not seenany work specificallyon computergenerated3D charcoalrendering.However, therehasbeensomenice work on graphitepencil renderingandmodelingblendersanderasersin the past[32, 33, 31]. This work achievesrealistic graphiteeffects by using detailedmodelsof pencilsanderasers.As aresult,thealgorithmis non-interactiveandtakesmanysecondsto rendereven small modelscomposedof a few hundredtriangles. We can envision situationsas in developing animationmoviesor visualizinglargescientificdata,wheretheusermaywantto getaquicklook at thedatafrom differentviewpointsevenbefore

decidingon moredetailedandelaboraterendering.Further, thereis also a needfor interactive systemfor applicationslike artisticvirtual environments.Our techniqueusestraditionalgraphicshard-wareto implementall the techniquesandthus, is moresuitedforsuchpurposes.

Our methodis basedon the following interestingobservationaboutthecharcoaldrawings. Charcoalis extremelylimited in dy-namicrangewhencomparedto thedynamicrangeof thephysicalworld, or evenotherdigital andnon-digitalmedia.So,it is indeeddifficult to capturemany rich colors and texturesusingcharcoal.Yet, anartist doesit with amazingease.Oneof thevery commontechniquesthat artistsuseto overcomethis limitation is to exag-geratethe contrastdifference.A relatedobservation wasmadein[6] while designinglighting model for non-photorealisticcoloredrenderingof mechanicalillustrations.This systemusedluminanceand hue shifts to createsuch lighting effects. We also usecon-trast enhancementwhile creatingcharcoalrenderingeffects. Weachieve this by usinga contrastmodifying functionwhich we callthe contrast enhancement operator (CEO). Similar techniqueshave alsobeenusedin [32, 31, 29,27, 28, 34, 35] wheretheprob-lem is viewedasa specialkind of half-toning.Thecontribution ofour techniquelies in thefactthatwe achieve many differenteffectsof charcoalrenderingusingthecommonframework of contrasten-hancement.

Theenhancementoperatoroperatesonauniformnoisetexturetogeneratea contrast enhanced texture which is texturemappedonthemodelto createthegrainy effect of charcoalrendering.Manypreviousalgorithmshave alsousedtexturemappingfor interactiveNPR.TheseincludeTonal Art Map describedby Praunet. al [23],prioritized stroke texturesusedby Winkenback[34] andSalisbury[27] andArt Mapsusedby Klein [12]. In theformertwo systems,onetexture is usedto convey a singletone. Thus,many suchtex-tureshave to be blendedtogetherin varying proportionsto createthe varying toneof a polygon [23]. This may lead to renderingsthatneedmultiple passes.We achieve the tonalvariationby usingonly oneCET. Thuswe do not needmulti-texturing or blendingtoachievetheeffectof charcoalrendering.Thoughartmapsuseasin-gle texture, this texture is dependenton thescenecontentwhereasour textureis independentof thescenecontent.

Thecontrastenhancementoperatoralsooperateson thecolor ofthe Phongshadedverticesof a model to generatewhat we call acontrast enhanced model. The color at verticesof the contrastenhancedmodelis usedto index into thecontrastenhancedtexturefor thefinal texturemapping.To createtheeffect of smudgingthecharcoalby hand,this texture mappedmodel is blendedwith thecontrastenhancedmodel.

Finally, we createwhat artistscall the closure effect wherethesilhouettesarenotexplicitly rendered,andtheclosureof theobjectis left to the interpretationof the viewer. Therehave beensev-eralmethodsthatusetraditionalgraphicshardwareto achieve realtime silhouettes[5, 7, 9, 16, 20, 24] andartistic silhouettes[20].However, renderingthetexturemappedmodelachievestheclosure

1

HarwareAcceleratedRealTime CharcoalRendering 2

Figure1: ConventionalCharcoalDrawings(Fromtop to bottomandleft to right ): (a) The abstractFitting (b) The Musician(c) Lady onHorse(d) SleepingDog(e) IndianWoman(f) TheGirl

effect withoutanexplicit computationof silhouettes.

1.1 Main Contributions

In summary, thefollowing arethemaincontributionsof this paper:� Contrast Enhancement Framework: Weachieve many dif-ferenteffectsof charcoalrenderingusinga commonframe-work of contrastenhancement.� Hardware Assisted Contrast Enhancement: We presentanew way of using the conventional graphicshardware thatis capableof doing Phongshading,to achieve a contrast-enhancedsmoothlyshadedmodel.� One Contrast Enhanced Texture: The contrastenhancedtexturecapturestheinformationof differenttonesin a singletextureandis obtainedby applyingtheenhancementoperatorona noisetexturethatconveys a uniformtone.� Hardware Accelerated One Pass Real Time RenderingSystem : We presenta singlepassrenderingalgorithmthatusesseveral featuresof traditional graphicspipeline to im-plementall thesetechniquesto generatea real-timecharcoalrenderingof 3D models.

In Section2, we describein detailssomeof theeffectsof char-coal renderingthat we simulatein our system. In Section3, wepresentthealgorithmoverview. In Section4, we describeour im-plementationusingthe traditionalgraphicshardware. Finally, wepresentthe resultsin Section5 andconcludewith future work inSection6.

2 Charcoal Rendering

It is impossibleto captureanartist’s creativity, renderingstyleandindividuality usingcomputergeneratedtechniques.However, therearesomebasicrulesthatall artistsuseextensively thatwecanstriveto achieve. In this section,we describea few suchbasictechniquesthatartistsfollow while usingcharcoalasa medium.

2.1 Contrast Enhancement

As mentionedbefore,artistsextensively usecontrastenhancementto overcomethe limited dynamicrangeof the charcoalmedium.This helpsthe artist to make the brightnessdifferencesmorepro-nouncedin orderto achieveasimilarperceptionof brightnessasthereal world within the limited dynamicrangeof themedium. Thistechniquehelpsto createvariouseffects like shadows andalsotoeffectively hidedetailsin non-illuminatedpartsof thescene.Thiscontrastenhancementis illustratedin the drawing of Figure1(a).Thespecularhighlight is shown asa sharpwhite contrastfrom thedarker sides.In thedrawing in Figure1(e),theshadows below thechinof thewomanhavebeenaccentuatedusingthesametechniqueandthehair on bothsidesof theheadaredarkenedto hidedetails.Thus,contrastexaggerationhashelpedthe artist to createa senseof volumeor 3D on the2D canvas.

2.2 Closure

Artists may sometimeslike to leave somepartsof the silhouetteunrenderedor very soft. The observer is allowed the freedomtoimagineandinterprettheeffect. This effect is termedby theartistsas the closure. Closureis alsousedto renderthe effectsof verybright light on theobject.Noticetheclosureon theleft sideof the


Figure2: TheAlgorithm


foreheadof themusicianin Figure1(b) andtheleft armandleg ofthe lady on horsein Figure1(c). In thepictureof thesleepingdogin Figure1(d),closureis usedon theright sideof thedog’s facetogettheeffectof brightsunlight.Also noticethatthistechniquedoesnothamperourperceptionof theshapeof theobjectin any way.

2.3 Smudging Effect

Artists usecharcoalin differentwaysto createdifferentrenderingstyles. Sometimescharcoalis usedlightly on coarsepaper. Thus,grainsof charcoalleft on thepapercreatesa grainy stroke appear-anceasin thedrawing of thegirl in Figure1(f). On theotherhandcharcoalmay be pressedhardon paperto leave larger numberofgrainswhicharethensmudgedby handto createtheeffectof vary-ing tonesof grayasin thepictureof themusician,theIndianwomanandthesleepingdog. The tonescreatedlikewisecanbevariedbyusingdifferentkinds of charcoalor by varying the pressurewithwhich thecharcoalis usedon thepaper.

3 Algorithm Overview

In thissection,wedescribethedesignof ouralgorithmfor charcoalrenderingof 3D modelsat interactive ratesthat createstheartisticeffectsexplainedin theprevioussection.This algorithmusescon-trastenhancementtechniquesto achieve theseeffects. Thesetech-niquesareacceleratedusingseveral featuresof traditionalgraphicshardwarein our implementation.

The stepsin our algorithm are shown in Figure 2. We applya contrastenhancementoperator(“operator”) on a noise texture(conveying anuniform tone)to generatethecharcoalgraintexture,which we referto ascontrastenhancedtexture(“texture”). We usethe samecontrastenhancementoperatorto modify the gray scalePhongshadedmodel. The modelthusmodifiedis calledthe con-trastenhancedmodel (“enhancedmodel”). In Section4, we willdescribehow we usetheconventionalgraphicshardwareto rendercontrastenhancedmodel.

We usetheenhancedmodelfor two purposes.Thecontrasten-hancedgrayvalueof theverticesof theenhancedmodelis usedtoindex into thetexturefor themappingof thegrainy textureontotheoriginal 3D model. The secondpurposeof this contrastenhancedmodelis to createthesmudgingeffect that is achievedby blendingthetexturedmodelwith theenhancedmodel.Finally, webumpmapa paper-texture in 2D on the renderedframeto impart the coarse-nessof thebackgroundpaper.

3.1 Creation of Contrast Enhancement Operator,Texture, and Model

In this section,we definecontrastenhancementoperators,contrastenhancedtexturesandenhancedmodels.

3.1.1 Contrast Enhancement Operators

A contrastenhancementoperator�

works on a gray scaletexture�or a grayshadedmodel � andmodifiesthemin sucha way so

as to increasethe perceived contrast. Thus,�

is a function thatmapsthe gray value � , �� , to anothergray value � ,�� . For example, �� is a contrastenhancementfunctionfor �� . A setof suchcontrastenhancementoperatorsareshown in Figure3 which vary in thevalueof � .

3.1.2 Contrast Enhanced Texture

In thisstep,weapplyacontrastenhancedoperator�

onanoisetex-turewhich conveys theappearanceof a uniform grainy tone. The

Figure3: Family of contrastenhancementcurvesof the form �� . Herewe show thecurveswith � equalto �� , �� and �� .contrastenhancedtexturethusgeneratedhelpsusto convey thein-formationof severaltonesin thesametexture.

A noisetexture is usuallygeneratedby placingblack grainsatrandomlocationsonasquarewhiteimage.Thedensityof thegrainssimulatesthegraininessof thecharcoalwhich canvary dependingonthetypeof charcoalandthepressurewith whichit is usedonthepaper. We canvary graindensityby changingthenumberof blackparticleson thewhite image.

Contrastenhancedtextureis generatedthesamewayanoisetex-tureisgenerated,exceptthatweapplythecontrastenhancementop-eratoron therandom� -coordinategeneratedfor every blackgrain.Finally, weblur thetextureto createthefinal contrastenhancedtex-ture. Figure4 shows two contrastenhancementoperatorsandthecorrespondingenhancedtexturesof varyinggraindensities.

3.1.3 Contrast Enhanced Model

We apply thecontrastenhancementoperatoron thegrayvaluesofthePhongshadedmodelto createthecontrastenhancedmodel.ThePhongshadinggivesa perceptionof thecurvatureof thesurfaceasit is derivedfrom thesurfacenormalandthelight position.Apply-ing theoperatoronthecolorsof thismodelpronouncestheshadowsandcurvesandthusenhancestheperceivedsenseof ‘volume’ and3D shape.

Notice that in Figure4 the planartexturesimpart a perceptionof 3D. They look curved and the perceived curvaturevarieswithdifferentoperatorsandgraindensities.Thisis exactlythetechniqueartistsuseto createwhatthey call asenseof ‘3D volume’. Applyingthe operatorto the Phongshadedmodel impartsa similar effect.Figure2 shows themodelbeforeandaftertheoperatoris applied.

3.2 The Grainy Stroke Effect

Theeffect of grainy strokesarebroughtaboutby texturemappingthe contrastenhancedgrainy texture on to the original 3D model.Thegrayvaluesof thecontrastenhancedmodelis usedto find thesetexture coordinates.Figure 5 shows the effect of using the grayvaluesof thePhongshadedmodelastexturecoordinatesinsteadofthegrayvaluesof thecontrastenhancedmodel.This illustratestheimportanceof theoperatorin renderingthegrainy strokes.

3.3 The Smudging Effect

The renderingat this point, with only the grainy texture on themodel,lackstheeffectof smudgingthecharcoalwith handto createsmoothtonalvariations.Interestingly, theblendingof this texturedmodelwith the contrastenhancedmodelbringsaboutthis effect.Referto Figure2 to seethiseffect.


Figure4: CETsof varyinggraindensitygeneratedby applyingdifferentCEOs

3.4 The Paper-Texture Effect

Finally, to createtheeffect of a coarsepapercanvas,we bumpmapa papertexture on the renderedframein 2D. The papertexture iscreatedby embossinga noiseimage. Notice that, this is differentfrom the3D bumpmappingusedin [1] to createthesameeffect. In[1], thepapertexturehasto bescaledappropriatelyif themodelisscaled,to maintaincoherence.Sinceweusea2D bumpmapontherenderedframe,thepapertextureremainsthesameevenwhenthemodelis zoomedin or out. Further, a 2D bumpmapsimulatesthepaper/canvasappropriatelysincethe coarsenessof the paperdoesnotchangewith thechangingcontentof therendering.

4 Real Time Rendering

In this section,we describeour singlepassrenderingtechniquetoimplementthe algorithm presentedin the previous sectionwhichgeneratescharcoalrenderingof 3D modelson traditionalgraphicspipeline at interactive rates. We use ! to denotethe normalat avertex and " to denotethelight vectorfrom thelight positionto thevertex. We usetheoperatorsof theform #%$'&)(+*�&-, , .0/21�3 4 . Wecanalsospecifya piecewiselinearoperator.

4.1 Contrast Enhanced Texture

Wegenerateasetof contrastenhancedtexturesusingdifferentcon-trastenhancementoperatorsandgraindensitiesasshown in Figure4, asa partof preprocessing.At run-time,we useoneresidenttex-ture at a time to texture map the whole model. The texturesareswitchedin orderto changetherenderingstyle.For example,if wewant to rendertheeffectsof a softercharcoal,we useanenhancedtextureof a greatergraindensity.

4.2 Contrast Enhanced Model

The way we createa contrastenhancedmodel is interestingsinceweusetheconventionalgraphicshardwarefor thispurposeandwedo not explicitly computethe contrastenhancement.Oneway toenhancethe shadingof the model is to calculatethe gray valuesat theverticesof thepolygonsusingthePhongshadingmodel,and

thenapplytheoperatoronthesegrayvaluesto enhancetheshadeateachvertex. ThenGouroudshadingcanbeemployedto interpolatethe valuesof the enhancedshadingwithin the polygon. But theGouroudshadingintroducesbandingeffectsdue to discretizationandrasterizationprocess.But thesameresultwithout thebandingartifactscouldbeachievedusingPhongshading.The following isthe equationof the color we would like to achieve in the interiorof thetriangle,but without muchof artifacts.Thisusesbarycentriccoordinates5 and 6 , thevertex normals798 , 7;: , and 7;< , andthelight vector(at infinity) " .5+#%$=7 8?> "?(A@6B#%$=7 :C> "?(A@�$D1CE�5�E�6B(F#%$=7 <G> "?( (1)

In our application,we useno specularlighting componentandhencewe areconcernedonly aboutthe diffusedlighting. We as-sumea white coloredmodelandwhite coloredlight with a coeffi-cientof diffusedlighting of 1�3 4 . Thus,thediffusedlighting at anypoint is exactlyequalto thedot productof thenormalandthelightvector.

Let us try to approximatethe effect of Equation1 to somerea-sonableaccuracy usingPhongshadingsothatwe geta continuousshading.We achieve this by scalingthenormalsin sucha way thatEquation1 is satisfiedat thevertices.(At theverticesof thetrian-gle,oneof 5 , 6 and 1?E05HE�6 is 1 andtheothersare 4 ). Thescalefactorthuscomputedis IBJLKNM OQPK�M O . Henceattheverticesof thetrianglewegetthefollowing shadingexpressionasrequiredby Equation1.R #%$'! > "?(! > " !AS > "* #%$'! > "T($'! > "T( $'! > "U(+*�#%$'! > "?(WVThenwerenderthismodelusingPhongshadingto achievethegrayscaleenhancementwithin thepolygon. In the interior of thetrian-gle,we getXUY $'5+#%$=7Z8 > "T(A@6B#%$=7;: > "?([@\$D1GE�50E�6B(F#%$=7]< > "?(F(where

Xis a varying scalefactor to normalizethe normal vector.

Thus,wemaintaintherequiredresultsat theverticesof thetriangle,andthePhongshadinggivesusresultsthataregoodin theinteriorof thetrianglealso.

In summary, thismethodhelpsusin two ways.First,weareableto usethe hardwareto achieve the contrastenhancedcolors. Sec-ond,wegetrid of bandingartifactscausedby theGouroudshading.


Figure5: Left : Themodel,texturemappedusingthePhongshadegrayvaluesasan index to theCET Right : Themodel,texturemappedusingthegrayvaluesof thecontrastenhancedmodelasanindex into CET.

4.3 Smudging Effect

To createthesmudging, we againusethegraphicshardwarecapa-bility of blendingcolorswith texturemappedpolygons.Wemodu-latethetexturedmodelby theenhancedgrayvaluesof theenhancedmodelgeneratedby the methodmentionedabove. This producesnicesmudgingeffectsasshown in theFigures6 and7.

4.4 Paper Texture

We generatepapertexturesof varying coarsenessby embossinganoisetextureandthencompressingits rangenearthewhite regionof the gray scale. After renderingthe texturedmodel,we usethehardwareacceleratedalphablendingto bumpmapthepapertextureon therenderedframe.

With the above systemimplementation,we can interactivelychangebetweendifferent operators,grain density factors,papercoarseness,andsmudgedor unsmudgedrenderingstyles.

5 Results and Discussions

In Figures6 and7 we presenta few of our resultsusingdifferentcontrastenhancementoperators,differentgraindensityfactors,andsmudgedandunsmudgedstyles.Thesearegeneratedusingunopti-mizedcodeonSGIO2R10000processor. Noticetheclosureeffectattainedon theleft teapot,thehumpof theleft pig andthemissile.The closureeffect is attainedwhenwe uselow grain densityfac-tors,high contrast,andhave thesmudgingoff. Also noticethatwecanproducedifferentdrawing stylesfrom light sketchydrawings(left teapot,right plane)andlightly shadeddrawings(missile,pig)to highly silhouettedsmudgeddrawings(bunny, venusandothers).Further, we can handlemodelswith complex curves and bends,startingfrom ^`_�a�a polygons(teapot)to _cb�a�a�a polygons(bunny)at interactive ratesof d�a framespersecond.

We have portedour algorithmon to regularPCshaving NVidiaGeforcegraphicscards. Figure8 shows our resultson PC whenusingour techniqueson largescientificdataof thousandsof poly-gons.Themodelsshown herehavemorethanonemillion triangleseach.

We have alsoinvestigatedusingdifferentcontrastenhancementoperatorsfor generatingtheenhancedtextureandthe contrasten-hancedmodel. We have useda gammafunction asmentionedinSection3 tocreatetheenhancednoisetexturewhileapplyingauser-definedpiecewiselinearoperatorto generatethecontrastenhancedmodel.Oncethesetwo modelsareblended,theresultcreatesadif-ferentstyle of charcoalrenderingas illustratedby the left Venusmodelof Figure6 andtheheadin Figure7.

In theaccompanying videoweillustratetheinteractiverenderingof variousmodels.Sincewe usea singlenoisetexture,we do notseeany temporalpoppingartifactswhile zoomingin andout. Sinceour enhancedtexturesareuniform in onedimensionandnot in theother, weseesomespatialdiscontinuitieswhenwezoomverycloseto the model. We areinvestigatingif we canuse‘lappedtexture’[22, 23] to achieve betterspatialcoherency. We arealso investi-gatinggeograftal/particletechniques[11, 17] to avoid any temporalartifactswhatsoever.

6 Summary and Future Work

In summary, we presentedanalgorithmthatgeneratesdifferentef-fectsof charcoaldrawing of 3D modelsusingthecommonframe-workof contrastenhancement.Thecontrastenhancementoperatorscanbeappliedon texturesandcolorsto achieve non-photorealisticeffects. This alsohelpedus to achieve theclosureeffect. Further,weimplementedthisalgorithmasasinglepassrenderingtechniqueto rendercharcoaleffects at interactive ratesusing available fea-turesin thetraditionalgraphicspipeline. We hopeto continuethisresearchin thefollowing directions.Different Contrast Enhancing Operators: We believe that con-trastenhancementoperatorsarepowerful enoughto generatedif-ferentNPReffects.For example,a stepfunctioncontrastenhance-mentoperatorcanbe usedto generatecartoonrenderingssimilarto thosedescribedin [1]. It would be worth determiningif sev-eralNPReffectscanbeunifiedundertheumbrellaof thecontrastenhancement.More Sketch Strokes: Our charcoalrenderinglacksrich strokeslike the onesin the drawing of the girl in Figure1. It is interest-ing to ponderhow wemightusedifferenttextures(insteadof noise


Figure6: Results(Row wisefrom topto bottom):(a)Theatticmodel(50,000triangles)renderedwith andwithoutsmudging.(b) TheTeapot(1600triangles)renderedusingtwo differentcontrastenhancementoperators.(c) The VenusModel (6000polygons)renderedusingtwodifferentcontrastenhancementoperators.(d) Babe,thepig (3000polygons)renderedusingtwo differentgraindensityfactors.


Figure7: Results(Left to RightandTop to Bottom): (a)TheStanfordBunny (65000polygons)(b) TheMissile (3000polygons)(c)TheFace(13000polygons)with smudgingoff (d) The Facewith smudgingon (e)ThePlane(9000polygons)with smudgingon (f) The Planewithsmudgingoff


Figure8: Visualizationof largecomplex scientificmodelusingcharcoalrendering

texture)to createa stroke textureanduseit in additionto thegraintextureto createricherstrokes.Temporal and Spatial Coherence: We would like to investigatethe temporalandspatialcoherency of the interactive charcoalren-deringin detailsothatthealgorithmcanbeusedfor animations.Radiating Silhouettes: A renderingstylequitecommonlyusedbyartists is to draw radiatingstrokes moving away from the objectsilhouettein the backgroundasin Figure1(a). It requireshumancreativity andaestheticsto usethis styleeffectively. However, thequestionis, canwefind awayto createthiseffectusingcomputers?Different styles in the same drawing: Artists alsousedifferentstyles in the samedrawing. For example, in the drawing of theIndianWomanin Figure1e,somepartsof thedrawing aresmudgedby handwhile othersarenot. Thoughan artist useshis creativityto decideon this,we would like to find anautomaticway to switchbetweenstyleswithin the sameframeto createartistically vibrantpictures.

Acknowledgements: We acknowledgeLaurenKroiz andMichaelPapkaof ArgonneNationalLaboratoriesfor usingouralgorithmonlargescientificdataandsharingtheresultswith us.

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