A Non-Photorealistic
Model for Automatic
Technical Illustration
Amy Gooch Bruce Gooch
Peter Shirley Elaine Cohen
SIGGRAPH 1998
Presented by Anteneh
Outline
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Introduction
Motivation
Related/previous work
Illustration Techniques
Automatic Shading Model
Conclusion and Future work
Introduction
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Method to automate some technical illustration
conventions.
Technical illustrations: in textbooks, reference
books, manuals i.e. a car owner’s manual.
Method: a shading algorithm based on edges,
highlighting and cool-to-warm tones.
Technical Illustrations
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Communication of geometry and form is more
important than aesthetics or realism.
Edge lines are usually emphasized.
Important three-dimensional properties are
preserved while extraneous detail is diminished.
Shadows are usually not included
Only one light is usually used
Motivation
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Technical illustrations tend to show more
information about the shape and function of an
object compared computer generated images.
Motivation
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Same comparison between technical illustrations
and photographs
Use color to differentiate parts
http://www.khulsey.com/stockauto.html
Related Work
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Very little previous work in graphics related to
technical illustration (1998).
[Saito and Takahashi 90] – techniques to show
geometric properties of objects.
Related work
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[Dooley and Cohen 1990] – Automatic
illustration of 3D geometric objects.
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use user-defined hierarchy of components (i.e. line
width, line boundary conditions) to generate
illustrations
http://portal.acm.org/ft_gateway.cfm?i
d=91422&type=pdf&coll=GUIDE&dl
=GUIDE&CFID=59921272&CFTOK
EN=37584317
Related Work
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[Williams 91] – global illumination
approximation using warm-to-cool tones and
drawing conventions for specular objects.
Illustration Techniques
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Observed illustration characteristics:
edge lines, the set containing surface boundaries,
silhouettes, and discontinuities, are drawn with black
curves.
 objects are shaded with intensities far from black or
white with warmth or coolness of color indicative of
surface normal;
 a single light source provides white highlights.
 shadowing is not shown.
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Illustration Techniques
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Subjects can infer at least as much geometric
information from edge lines in drawn images
verses shaded or textured images.
Hue changes are used to indicate surface
orientation rather than reflectance.
Automatic Illustration Method
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Automate the mentioned illustration
characteristics.
Edge lines are drawn in black
Highlights are drawn using traditional term from
the Phong shading model.
Shade the surfaces of objects
Automatic Illustration Method
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Traditional diffuse shading method calculates
luminance as follows:
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Tone-based shading
Shading metal Objects
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Traditional shading
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kd = 1, ka = 0
The image hides shape and material information
in the dark regions.
Traditional shading
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Additional information can be provided by
highlights (direction of light) and edge lines
(divisions).
Image
produced by
adjusting kd
and ka
Traditional shading
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Combining the shaded and illustrated model.
Poor image and loss of detail, not automated.
Tone-based shading
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Tones : color scales created by adding grey to a
certain color.
Tones are important to illustration, especially
when restricted to a limited luminance range.
Temperature : used to give depth cue. Warm
colors advance, cool colors recede.
Warm – red, orange, yellow
 Cool – blue, violate, and green
 Temperate – red-violets, red-greens
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Creating a tone
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Tone for a pure red object: sum blue-to-yellow
and dark-to-red to tone.
Tone-based shading
Tone-based shading
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Generalize the classic shading model to
experiment with tones using the cosine term:
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Use blue and yellow as two temperature
extremes:
Tone-based shading
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Combining luminance shift (traditional shading),
tone and temperature based shading.
b = 0.4, y = 0.4
,
= 0.2, and = 0.6
Tone-based shading
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The different values of b and y determine the strength
of the overall temperature shift, where as and
determine the prominence of the object color, and the
strength of the luminance shift.
b = 0.55, y = 0.3
,
= 0.25, and = 0.5
Shading of Metal Objects
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Technical illustrators use a different technique to
communicate whether or not an object is metal.
Illustrators represent a metallic surface by
alternating dark and light bands.
Method: map a set of twenty stripes of varying
intensity along the parametric axis of maximum
curvature.
Shading of Metal Objects
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Phong vs metal-shading
Shading of Metal Objects
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metal-shading with edge and cool-to-warm shift
Colored Objects
Conclusion:
 An
automated technical illustration method is
presented using edge lines, highlighting, colorshifts and metal-shading.
Future Work:
 Improvements
in illustration rules
 Automate other illustration forms
 Interactive illustration
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