CS-184: Computer Graphics Announcements - University of ...

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CS-184: Computer Graphics Announcements - University of ...

CS-184: Computer GraphicsLecture 23: Non-Photorealistic RenderingManeesh AgrawalaUniversity of California, BerkeleyAnnouncementsFinal Project: multiple due dates• Project proposal due Wed Nov 17, 11pm• Progress report 1 due Mon Nov 22, 11pm• Progress report 2 due Wed Dec 1, 11pm• Final report due Wed Dec 8, 11pm3


Conveying ShapeLinesShadingFrom Gooch 2 4TopicsPhotographs vs. drawingsTypes of linesLines of curvatureSilhouettes and contoursGraphical drawing conventionsTexture and toneEffects of drawing style5


A photographic depiction capturesthe exact appearance of theobject as we actually see itSubtle, complex details ofcoloration and texture are fullyrepresented, with greataccuracyPhotograph of the right hip bone (lateral aspect).Johannes W. Rohen and Chihiro Yokochi.Color Atlas of Anatomy:A Photographic Study of the Human Body,Igaku-Shoin, 1993.A drawing offers thepossibility to clarifystructural or conceptualinformation that may bedifficult to perceive in evena very good photo.Color drawing of the same subject.Sobotta Atlas of Human Anatomy, 11th Englishedition, vol. 2, edited by Jochen Staubesand,translated and edited by Anna N. Taylor,Urban & Schwarzenberg, 1990.Photo vs. Drawingin ArchaeologyJames B. Porter. “Relief Monuments”, inThe Student's Guide to Archaeological Illustrating,Brian D. Dillon, ed., Institute of Archaeology,University of California, Los Angeles, 1981


Normal CurvatureCurvature applet: http://www.ies.co.jp/math/java/calc/curve/curve.html22Space Curve23Curvature of SurfacesHilbert and Cohn-Vossen [1952]Geometry and the Imagination24


Curvature of SurfacesHilbert and Cohn-Vossen [1952]Geometry and the Imagination25Curvature of SurfacesHilbert and Cohn-Vossen [1952]Geometry and the Imagination26Curvature of SurfacesHilbert and Cohn-Vossen [1952]Geometry and the Imagination27


Curvature of SurfacesHilbert and Cohn-Vossen [1952]Geometry and the Imagination28Principal CurvaturesHilbert and Cohn-Vossen [1952]Geometry and the Imagination29Artistic InspirationRussell Drake’s “single linesystem of shading” the flow of the shape is conveyedthrough the directions of thecarefully drawn strokesLumbosacral and Sacro-iliacfusion . Russell Drake,medical illustrator, MayoFoundation, 1932.


V. Interrante31Principal DirectionsKlein bottleFrom Hertzmann and Zorin32Guassian CurvatureK 1= curvature in first principal directionK 2= curvature in second principal directionGaussian curvature: K = K 1K 2Mean curvature: H = (K 1+ K 2) / 2K > 0 : elliptic, convex or concaveK < 0 : hyperbolic, saddle-shapedK = 0 : parabolic, cylindrical or planar33


Gaussian Curvature34Parabolic LinesFelix Klein: Apollo35Silhouettes and Contours


Suggestive ContoursDeCarlo, Finkelstein, Rusinkiewicz, Santella, Suggestive contours forconveying shape, SIGGRAPH 200340Suggestive Contours - DEMOSilhouettes aloneSilhouettes + suggestive contours41Graphical Drawing Conventions


Drawing ParametersHaloed linesTaper near t-junctionControl of line weightHighlightingEye-lashingSketchiness4345


Illustration Rules (Dooley & Cohen)Importance• Low• Medium• HighTypes• Boundaries• Creases• Silhouettes• Isoparametric46Line WeightSingle weight Two weights Distance weightingFrom Martin (reproduced in Gooch and Gooch)47


Highlighting49Texture and Tone


Arthur L. Guptill (1976) Rendering in Pen and Ink, Watson-Guptill Publications, figure 94Stroke CollectionsPrioritized Stroke Textures[Salisbury et al. ’94][Winkenbach et al. ’94]Art Maps[Klein et al. 2000] scale tone 53Pen and Ink Illustration [Winkenbach and Salesin 94] texture tone 54


Pen and Ink Illustration [Winkenbach and Salesin 94]Collection of stroke imagesWill blend → design with high coherenceStroke nesting property scale tone 55Pen and Ink Illustration [Winkenbach and Salesin 94]56Pen and Ink Illustration [Winkenbach and Salesin 94]57


Effects of Drawing StyleAssessing the effect of non-photorealisic rendered imagesin CAD, Schumann, Strothotte, Raab, Laser, CHI 96Comparison:CAD59Comparison: Shaded60


Comparison: Sketch61Draft vs. Presentation62Affect vs. Cognition63


SummaryIllustrations often better than photographs Enhance important features Deemphasize unimportant detailGrand challenge Produce a good line drawing What lines, not just how to draw lines64

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