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Rendering Fur with Rendering Fur with Three Dimensional Three Dimensional TexturesTextures
James T. Kajiya and Timothy L. KayJames T. Kajiya and Timothy L. Kay
MotivationMotivation
We want to be able We want to be able to render furry to render furry things!things!
http://www.lesleymattuchio.com/Ladies.html
http://www.trappersden.ca/Moxy.JPG
Previous WorkPrevious Work
Geometrically accurateGeometrically accurate– Brute-force rendering of individual Brute-force rendering of individual
hairshairs– Very slowVery slow– Severe aliasing due to micro-Severe aliasing due to micro-
geometrygeometry Particle-based systems for Particle-based systems for
Volume renderingVolume rendering– Not optimal for ray tracingNot optimal for ray tracing
Volume DensitiesVolume Densities
Blinn (1982)Blinn (1982)– Method for rendering volume densitiesMethod for rendering volume densities– Volume of microscopic spheresVolume of microscopic spheres– Assumed Homogeneous mediaAssumed Homogeneous media
Kajiya and Von Hersen (1984)Kajiya and Von Hersen (1984)– Generalized to non-homogeneous Generalized to non-homogeneous
mediamedia– Volume rendering for ray tracingVolume rendering for ray tracing
Volume DensitiesVolume Densities
For each ray through the volume…For each ray through the volume…– Find the transparency of the surfaceFind the transparency of the surface
– Find the brightness of the surfaceFind the brightness of the surface
Volume densitiesVolume densities
Three parts of the brightness integral
Visibility of the current position in the volume
Sum of the light contribution from each light source
The density of the surface at the point
TexelsTexels
Replace volume densities with Replace volume densities with texels: texels: 3D array containing 3D array containing microsurface datamicrosurface data– Density:Density: relative projected area of a relative projected area of a
surface inside the volume cellsurface inside the volume cell– Frames: Frames: Local direction of the surfaceLocal direction of the surface– Lighting Model: Lighting Model: The lighting model The lighting model
for the local surfacefor the local surface
TexelsTexels
Can we render texels Can we render texels with the original with the original volume density volume density rendering equations?rendering equations?– All line integrals go to All line integrals go to
00– Transparency and Transparency and
brightness brightness calculations both go calculations both go to 0!to 0!
TexelsTexels
Solution: replace all integrals with sumsSolution: replace all integrals with sums– Transparency equation becomesTransparency equation becomes
– Brightness equation becomesBrightness equation becomes
Fur RenderingFur Rendering
Four steps to rendering fur:Four steps to rendering fur:– Create fur texelCreate fur texel– Map texels to world spaceMap texels to world space– Shoot rays into texelShoot rays into texel– Calculate lightingCalculate lighting
Fur RenderingFur Rendering
Create Fur TexelCreate Fur Texel– Each hair is a cylinderEach hair is a cylinder– Place hairs randomly Place hairs randomly
on a surfaceon a surface– Model overcoat and Model overcoat and
undercoatundercoat– Jiggle until it looks Jiggle until it looks
“correct”“correct”
Fur RenderingFur Rendering
Map texels to world Map texels to world spacespace– Create a continuous Create a continuous
mapping between mapping between texel and modeltexel and model
– Interpolate between Interpolate between texels to form a texels to form a bilinear patchbilinear patch
– No geometry is No geometry is neededneeded
Fur RenderingFur Rendering
Shoot rays into texelShoot rays into texel– Intersect rays with bilinear texel patch in Intersect rays with bilinear texel patch in
world spaceworld space– Convert intersection into texel spaceConvert intersection into texel space
Calculate LightingCalculate Lighting– Fur lighting model is diffuse and specularFur lighting model is diffuse and specular– Diffuse based on cylindrical shapeDiffuse based on cylindrical shape– Specular is modified Phong lightingSpecular is modified Phong lighting
ResultsResults
ResultsResults
ConclusionConclusion
Fur rendering using 3D texturesFur rendering using 3D textures– New 3D texture model called texelNew 3D texture model called texel– New rendering equations for New rendering equations for
microsurfacesmicrosurfaces– Fur texel modeling techniqueFur texel modeling technique– Texel mapping/interpolation to form Texel mapping/interpolation to form
objects without geometryobjects without geometry– Fur lighting BRDFFur lighting BRDF
Pros/ConsPros/Cons
ProsPros– Very realistic results!Very realistic results!– Complete description of methodComplete description of method– Great reference images for comparison Great reference images for comparison
with faster methodswith faster methods– Easily extendableEasily extendable
ConsCons– Fairly slow (2 hrs on a 16 processor Fairly slow (2 hrs on a 16 processor
mainframe)mainframe)
QuestionsQuestions
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