A Non-Photorealistic Lighting Model For Automatic Technical Illustration Presented by: Chris Lattner April 8, 2003 CS497yzy

Motivation n Provide automated technical illustration: –Used to visualize complex 3D shapes –Used for technical manuals, textbooks, encyclopedias, … n Produce static 2D images: –motion, accommodation, and parallax cues are not available to the viewer –Must overcome this limitation to be useful

Approach n Expression of shape and form important –Provide high-contrast object outlines –Use hue-based shading for object interiors n Precise shape detail is important: –Albedo information is much less so n Expresses the overall form of an object

Illustration Techniques –Edge lines (surface boundaries, silhouettes, and discontinuities) drawn with black curves –Shadowing is ignored –Matte objects are shaded with mid-level intensities, indicating normal with warmth or coolness of color (from one light source) –Phong style highlights still drawn –Metal objects are shaded as if extremely anisotropic

Shading for Matte Objects n Lambertian model loses too much information: –Edge lines are invisible in low-intensity regions –Highlights invisible in high-intensity regions n Shading through intensity will not work: –instead, shade primarily through tone (hue)

Shading through tone n New shading model: –Small intensity changes –Large hue changes n Blue to Yellow n Cool to warm transition n Reduce importance of base object color: –Allows highlights and edge lines to stand out n Linear interpolate sum of two contributions

New formulation

Shading of Metal Objects n Illustrators use alternating light and dark bands to simulate extreme anisotropism n Anisotropic reflection comes from milling process often used n Simulate using a map of 20 bands of random intensity, mapped along axis of maximum curvature

Example of a metallic part New Algorithm Phong Shading

With base object color New Algorithm Phong Shading

Conclusion n New approach for technical illustration n Efficient implementation (similar to diffuse shading) n Emphasizes important details n Can handle metallic objects