NPR Today Art Based Rendering of Fur Grass and Trees Michael A Kowalski et al SIGGRAPH 99 A Non Photorealistic Lighting Model for Automatic Technical Illustration Amy Gooch Bruce Gooch Peter Shirley and Elaine Cohen SIGGRAPH 98 04 01 05 2005 University of Wisconsin Art Based Rendering of Fur Grass and Trees Michael A Kowalski et al Presented by Scott Finley 04 01 05 2005 University of Wisconsin Introduction Highly detailed objects containing fur grass etc are expensive to render This paper attempts to use a well known artistic technique to indicate complexity with simple shapes 04 01 05 2005 University of Wisconsin Goals 1 2 3 04 01 05 Give the designer control over the style Simplify modeling by making rendering strategy an aspect of modeling Provide interframe coherence for the styles developed 2005 University of Wisconsin Prior Work Reeves used particle systems to create complex geometry from simple shapes Alvy Ray Smith used particles and graftals to create his Cartoon Tree Badler and Glassner generalized the idea of graftals This paper uses a modified version of difference images proposed by Salisbury et al 04 01 05 2005 University of Wisconsin More Prior Work Meier s particle based brush strokes showed non geometric complexity and fixed particle spacing on objects 04 01 05 2005 University of Wisconsin Software Framework Models are broken into patches Each is rendered by a procedural texture Two types of reference images are used 1 2 Color reference image ID reference image 04 01 05 Provides patches with list of pixels Can be used to find visibility of known point 2005 University of Wisconsin Graftal Textures Place fur leaves grass etc on geometric models Need to be drawn in a controlled way in screen space Need to stick to models for inter frame coherence 04 01 05 2005 University of Wisconsin Before 04 01 05 2005 University of Wisconsin After 04 01 05 2005 University of Wisconsin Difference Image Algorithm Each patch draws its region in the color reference image Darker areas indicate more desire for graftals to be placed In the examples here we want graftals along the silhouettes Render with point light at camera Can be done explicitly by designer Bear s feet 04 01 05 2005 University of Wisconsin Difference Image Cont Graftals are placed according to the desire in the color reference image This allows screen space density to be controlled Bin all the pixels according to the desire level and start placing graftals on the pixels with the highest desire 04 01 05 2005 University of Wisconsin Creating Inter frame Coherence Need to be sure that graftals persist across frames to avoid extreme noise etc In first frame place graftals according to DIA In further frames attempt place graftals from previous frame Place new graftals where needed according to the DIA 04 01 05 2005 University of Wisconsin Subtracting Blurred Image When a graftal is placed it subtracts a blurred image of itself from the reference image Graftals are treated as a point for this The image is a Gaussian dot Size of the dot is proportional to the screen space area of the graftal 04 01 05 2005 University of Wisconsin Graftal Sizing Graftals can be set to scale according to perspective have a constant size or somewhere between Graftal size can be reduced if it tries to draw itself but there isn t enough desire 04 01 05 2005 University of Wisconsin Drawing Graftals Fur graftals can be drawn at drawn at different details with triangle strips Drawing happens in surface normal plane Detail depends on angle to viewer 04 01 05 2005 University of Wisconsin Future Work Reduce flicker popping as graftals enter and leave 04 01 05 Use alpha blending Put graftals on the back of objects Use several layers of statically placed graftals 2005 University of Wisconsin New Styles Dual layered fur Suggests complex lighting 04 01 05 2005 University of Wisconsin 04 01 05 2005 University of Wisconsin A Non Photorealistic Lighting Model for Automatic Technical Illustration Amy Gooch Bruce Gooch Peter Shirley Elaine Cohen SIGGRAPH 98 presented by Tom Brunet University of Wisconsin Madison CS779 Background Various NPR Techniques Cassidy J Curtis Sean E Anderson Kurt W Fleischer and David H Salesin Computer Generated Watercolor In SIGGRAPH 97 Conference Proceedings August 1997 Technical like Takafumi Saito and Tokiichiro Takahashi Comprehensible Rendering of 3D Shapes In SIGGRAPH 90 Conference Proceedings August 1990 Doree Duncan Seligmann and Steven Feiner Automated Generation of Intent Based 3D Illustrations In SIGGRAPH 91 Conference Proceedings July 1991 Debra Dooley and Michael F Cohen Automatic Illustration of 3D Geometric Models Surfaces IEEE Computer Graphics and Applications 13 2 307 314 1990 04 01 05 2005 University of Wisconsin Contributions Reduction of dynamic range needed to portray shape NPR method for appearance of metal 04 01 05 2005 University of Wisconsin Diffuse Shading ka ambient illumination kd diffuse reflectance 04 01 05 I k d k a k d max 0 l n 2005 University of Wisconsin Highlights and Edges 04 01 05 2005 University of Wisconsin Diffuse w Edges Highlights ka ambient illumination kd diffuse reflectance 04 01 05 I k d k a k d max 0 l n 2005 University of Wisconsin Alter Shading Model Want to keep lighting from above Extend shading across entire sphere 1 l n 1 l n kcool 1 k warm I 2 2 Finally mix a coolwarm hue shift with a luminance shift 04 01 05 2005 University of Wisconsin Near Constant Luminance 04 01 05 2005 University of Wisconsin Color Luminance Shift 04 01 05 2005 University of Wisconsin Maintains Color Name 04 01 05 2005 University of Wisconsin Metal Appearance Milling creates anisotropic reflection Pick 20 strips of random intensity 0 5 Linearly interpolate 04 01 05 2005 University of Wisconsin Metallic Anisotropic Reflection 04 01 05 2005 University of Wisconsin Approximate in OpenGL Two opposing directional lights kwarm kcool 2 kcool kwarm 2 Ambient kcool kwarm 2 04 01 05 2005 University of Wisconsin Other Results Questions 04 01 05 2005 University of Wisconsin 04 01 05 2005 University of Wisconsin Computer Generated Watercolor Siggraph 1997 Cassidy J Curtis Sean E Anderson Joshua E Seims Kurt W Fleischer David H Salesin 04 01 05 2005 University of Wisconsin Watercolor Effects Drybrush Edge Darkening Backruns Granulation Flow Effects Glazing 04 01 05 2005 University of Wisconsin Previous Work David Small Simulating watercolor by modeling diffusion pigment and paper fibers February 1991 Qinglian Guo and