A A Non-Photorealistic Lighting Non-Photorealistic Lighting Model For Automatic Technical Model For Automatic Technical

IllustrationIllustration

Presented by: Chris LattnerPresented by: Chris LattnerApril 8, 2003April 8, 2003

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MotivationMotivation

Provide Provide automatedautomated technical technical illustration:illustration:– Used to visualize complex 3D shapesUsed to visualize complex 3D shapes– Used for technical manuals, textbooks, Used for technical manuals, textbooks,

encyclopedias, …encyclopedias, … Produce static 2D images:Produce static 2D images:

– motion, accommodation, and parallax motion, accommodation, and parallax cues are not available to the viewercues are not available to the viewer

– Must overcome this limitation to be usefulMust overcome this limitation to be useful

ApproachApproach

Expression of shape and form Expression of shape and form importantimportant– Provide high-contrast object outlinesProvide high-contrast object outlines– Use hue-based shading for object interiorsUse hue-based shading for object interiors

Precise shape detail is important:Precise shape detail is important:– Albedo information is much less soAlbedo information is much less so

Expresses the Expresses the overall formoverall form of an object of an object

Illustration TechniquesIllustration Techniques

– Edge lines (surface boundaries, silhouettes, Edge lines (surface boundaries, silhouettes, and discontinuities) drawn with black curvesand discontinuities) drawn with black curves

– Shadowing is ignoredShadowing is ignored– Matte objects are shaded with mid-level Matte objects are shaded with mid-level

intensities, indicating normal with warmth intensities, indicating normal with warmth or coolness of color (from one light source)or coolness of color (from one light source)

– Phong style highlights still drawnPhong style highlights still drawn– Metal objects are shaded as if extremely Metal objects are shaded as if extremely

anisotropicanisotropic

Shading for Matte ObjectsShading for Matte Objects Lambertian model Lambertian model

loses too much loses too much information:information:– Edge lines are invisible Edge lines are invisible

in low-intensity regionsin low-intensity regions– Highlights invisible in Highlights invisible in

high-intensity regionshigh-intensity regions Shading through intensity will not work:Shading through intensity will not work:– instead, shade primarily through tone (hue)instead, shade primarily through tone (hue)

Shading through toneShading through tone

New shading model:New shading model:– Small Small intensityintensity changes changes– Large Large huehue changes changes

Blue to YellowBlue to Yellow Cool to warm transitionCool to warm transition

Reduce importance of base object color:Reduce importance of base object color:– Allows highlights and edge lines to stand outAllows highlights and edge lines to stand out

Linear interpolate sum of two Linear interpolate sum of two contributionscontributions

New formulationNew formulation

Shading of Metal ObjectsShading of Metal Objects

Illustrators use alternating light Illustrators use alternating light and dark bands to simulate and dark bands to simulate extreme anisotropismextreme anisotropism

Anisotropic reflection comes from Anisotropic reflection comes from milling process often usedmilling process often used

Simulate using a map of 20 bands Simulate using a map of 20 bands of random intensity, mapped along of random intensity, mapped along axis of maximum curvatureaxis of maximum curvature

Example of a metallic partExample of a metallic part

New AlgorithmNew AlgorithmPhong ShadingPhong Shading

With base object colorWith base object color

New AlgorithmNew AlgorithmPhong ShadingPhong Shading

ConclusionConclusion

New approach for technical New approach for technical illustrationillustration

Efficient implementation (similar to Efficient implementation (similar to diffuse shading)diffuse shading)

Emphasizes important detailsEmphasizes important details Can handle metallic objectsCan handle metallic objects