Non-Photorealistic Rendering

FORMS

Mesh (~170)Mesh (~170) Parametric (~16)Parametric (~16)

Implicit/CSG (~9)Implicit/CSG (~9)

Volumetric (~28)Volumetric (~28)

3D Object Representation in NPR3D Object Representation in NPR

Point Cloud (~4)Point Cloud (~4)

Fundamental GoalsFundamental GoalsTraditional IllustrationTraditional Illustration

Create convincing impressions of 3D Create convincing impressions of 3D forms on paperforms on paper

Depict solid masses in spaceDepict solid masses in space

Show their various structural conditionsShow their various structural conditions

Suggest their different surface Suggest their different surface characteristicscharacteristics

Communication Pipeline in Communication Pipeline in Science IllustrationScience IllustrationCommunication Pipeline in Communication Pipeline in Science IllustrationScience Illustration

SCIENTISTSCIENTIST ILLUSTRATORILLUSTRATOR

Provides materialProvides material Requests informationRequests information

descriptiondescription Records informationRecords information

specimenspecimen Studies specimenStudies specimen

Makes rough drawingMakes rough drawing

Makes detailed preliminary drawingMakes detailed preliminary drawing

Checks detailed preliminary drawingChecks detailed preliminary drawing

Corrects preliminary drawingCorrects preliminary drawing

Checks correctionsChecks corrections

Produces renderingProduces rendering

Checks renderingChecks rendering

Labels drawingLabels drawing

Checks labelingChecks labeling

Return specimenReturn specimen

CompositionPrinciples

Finished Rendering

Initial SketchRendering

Techniques

Line (Ink)Scratch Board PencilCoquille BoardWash,…

Subject

AnatomyBotanyZoologyPaleontologyArcheology Study

Selection

FormsLighting

Steps

Study the Subject!Study the Subject!Illustration terminologyIllustration terminology

Communicate subtleties and eliminate ambiguitiesCommunicate subtleties and eliminate ambiguities

Move the subject around, do not just concentrate Move the subject around, do not just concentrate on one parton one part

Observe the general appearance firstObserve the general appearance first

Identify the most significant features Identify the most significant features

Only include detail which is necessary in your Only include detail which is necessary in your drawingdrawing

Study the Subject!Study the Subject!Illustration terminologyIllustration terminology

Extract major features (folding regions, surfaces areas, volumes, curvatures)

Highlights to visually eliminate extraneous details and reduce the subject to simple lights and darks

Textures, angles where different forms join, perspective, foreshortening

Analyze the Object!Analyze the Object!NPR terminologyNPR terminology

Exactly same goals as in traditional illustration!

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary

Outline : Model Boundary

Only in non-closed models

Polygonal model :

at least one polygon has at at least one polygon has at least one edge that is not least one edge that is not shared with any other shared with any other polygonpolygon

The vertex is adjacent to a boundary edge

Outline : Model Boundary Cusps (Vertex)

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary Silhouette

Outline : View Silhouette

Silhouette point : point on the surface where V (u, v) . N (u, v) = 0 or the angle between V(u, v) and N(u, v) is 900

Outline : View Silhouette

N . V < 0 N . V > 0

N . V = 0

Polygon is perpendicular to the view direction

An edge between two polygons is a silhouette edge

if the edge is shared by a front-facing and a back-facing polygon

The vertex is adjacent exactly 2 silhouette edges, one front-facing and the other back-facing

Outline : View Silhouette Cusps (Vertex)

The vertex is adjacent to more than 2 silhouette edges

Outline : View Silhouette Cusps (Vertex)

The vertex is adjacent exactly 2 silhouette edges, one front-facing and the other back-facing

The vertex is adjacent to more than two silhouette edges

Outline : Cusps (Vertex)

The vertex is adjacent to a boundary edge

Terminology on SilhouettesTerminology on Silhouettes

Traditional IllustrationTraditional IllustrationNPRNPR

ProfileProfile(Computer Vision, Modeling)(Computer Vision, Modeling)

SilhouetteSilhouette

BoundaryBoundary

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary Silhouette

X

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary

Crease(+ otherdiscontinuities)

Silhouette

X

Polygonal model: an edge between two front-facing polygonswhose dihedral angle theta is above some threshold

NURBS surface: any region where the surface normal changes abruptly, i.e., C1 discontinuities

Interior : Model/Threshold Crease

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary

Crease(+ otherdiscontinuities)

Crease(+ otherdiscontinuities)

Silhouette

X

Interior : Model/Threshold Other Discontinuities

Sousa et al., Precise Ink Drawing of 3D Models,

Eurographics 2003

Pulla, Pulla, Curvature Based Segmentation of 3D MeshesCurvature Based Segmentation of 3D Meshes, , Prism/3DKPrism/3DK ASU, 2000

Interior : Model/Threshold Other Discontinuities

Alliez et al., Anisotropic Polygonal Remeshing,

SIGGRAPH 2003

Interior : Model/Threshold Other Discontinuities

Interior : Model/Threshold Other Discontinuities

Sousa and Prusinkiewicz, A Few Good Lines: Suggestive Drawing of 3D Models,

Eurographics 2003

Sousa et al., Depicting Shape Features with Directional Strokes and Spotlighting, Computer Graphics International 2004

Interior : Model/Threshold Other Discontinuities

Model dependent

Threshold dependent

View dependent

Outline form of the object

Interior form of the object

Boundary

Crease(+ otherdiscontinuities)

Crease(+ otherdiscontinuities)

Silhouette

X

X

1979 1979 Appel et al Appel et al The haloed line effect for hidden line eliminationThe haloed line effect for hidden line eliminationSIGGRAPHSIGGRAPH

19821982 RothRothRay Casting for Modeling SolidsRay Casting for Modeling SolidsComputer Graphics and Image ProcessingComputer Graphics and Image Processing

19871987 Wyvill et alWyvill et alSketches by Ray TracingSketches by Ray Tracing Computer Graphics InternationalComputer Graphics International

19871987 SasadaSasadaDrawing Natural Scenery by Computer GraphicsDrawing Natural Scenery by Computer Graphics Computer-Aided DesignComputer-Aided Design

19871987 Kamada, T. and Kawai, S.Kamada, T. and Kawai, S.An Enhanced Treatment of Hidden LinesAn Enhanced Treatment of Hidden LinesACM Transactions on GraphicsACM Transactions on Graphics

19881988 Veenstra and Ahuja Veenstra and Ahuja Line drawings of octree-represented objectsLine drawings of octree-represented objectsACM Transactions on GraphicsACM Transactions on Graphics

Line Drawing of 3D Models

1979 1979 Appel et al Appel et al The haloed line effect for hidden line eliminationThe haloed line effect for hidden line elimination

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19871987 Kamada, T. and Kawai, S.Kamada, T. and Kawai, S.An Enhanced Treatment of Hidden LinesAn Enhanced Treatment of Hidden Lines

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19881988 Veenstra and Ahuja Veenstra and Ahuja Line drawings of octree-represented objectsLine drawings of octree-represented objects

Line Drawing of 3D Models