A Non-A Non-Photorealistic Photorealistic

Model for Model for Automatic Automatic Technical Technical

IllustrationIllustrationAmy Gooch Bruce GoochAmy Gooch Bruce Gooch

Peter Shirley Elaine CohenPeter Shirley Elaine Cohen

SIGGRAPH 1998SIGGRAPH 1998

Presented by Anteneh

OutlineOutline

IntroductionIntroduction MotivationMotivation Related/previous workRelated/previous work Illustration TechniquesIllustration Techniques Automatic Shading ModelAutomatic Shading Model Conclusion and Future workConclusion and Future work

IntroductionIntroduction Method to automate some technical Method to automate some technical

illustration conventions.illustration conventions. Technical illustrations: in textbooks, Technical illustrations: in textbooks,

reference books, manuals i.e. a car reference books, manuals i.e. a car owner’s manual.owner’s manual.

Method: a shading algorithm based Method: a shading algorithm based on edges, highlighting and cool-to-on edges, highlighting and cool-to-warm tones.warm tones.

Technical IllustrationsTechnical Illustrations

Communication of geometry and form Communication of geometry and form is more important than aesthetics or is more important than aesthetics or realism.realism.

Edge lines are usually emphasized.Edge lines are usually emphasized. Important three-dimensional Important three-dimensional

properties are preserved while properties are preserved while extraneous detail is diminished.extraneous detail is diminished.

Shadows are usually not includedShadows are usually not included Only one light is usually usedOnly one light is usually used

MotivationMotivation

Technical illustrations tend to show Technical illustrations tend to show more information about the shape more information about the shape and function of an object compared and function of an object compared computer generated images.computer generated images.

MotivationMotivation Same comparison between technical Same comparison between technical

illustrations and photographsillustrations and photographs Use color to differentiate partsUse color to differentiate parts

http://www.khulsey.com/stockauto.html

Related WorkRelated Work

Very little previous work in graphics Very little previous work in graphics related to technical illustration related to technical illustration (1998).(1998).

[Saito and Takahashi 90] – [Saito and Takahashi 90] – techniques to show geometric techniques to show geometric properties of objects.properties of objects.

Related workRelated work

[Dooley and Cohen 1990] – [Dooley and Cohen 1990] – Automatic illustration of 3D Automatic illustration of 3D geometric objects.geometric objects. use user-defined hierarchy of use user-defined hierarchy of

components (i.e. line width, line components (i.e. line width, line boundary conditions) to generate boundary conditions) to generate illustrationsillustrations

http://portal.acm.org/ft_gateway.cfm?id=91422&type=pdf&coll=GUIDE&dl=GUIDE&CFID=59921272&CFTOKEN=37584317

Related WorkRelated Work

[Williams 91] – global illumination [Williams 91] – global illumination approximation using warm-to-cool approximation using warm-to-cool tones and drawing conventions for tones and drawing conventions for specular objects.specular objects.

Illustration TechniquesIllustration Techniques

Observed illustration characteristics: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.

Illustration TechniquesIllustration Techniques

Subjects can infer at least as much Subjects can infer at least as much geometric information from edge geometric information from edge lines in drawn images verses shaded lines in drawn images verses shaded or textured images.or textured images.

Hue changes are used to indicate Hue changes are used to indicate surface orientation rather than surface orientation rather than reflectance.reflectance.

Automatic Illustration Automatic Illustration MethodMethod

Automate the mentioned illustration Automate the mentioned illustration characteristics.characteristics.

Edge lines are drawn in blackEdge lines are drawn in black Highlights are drawn using Highlights are drawn using

traditional term from the Phong traditional term from the Phong shading model.shading model.

Shade the surfaces of objectsShade the surfaces of objects

Automatic Illustration Automatic Illustration MethodMethod

Traditional diffuse shading method Traditional diffuse shading method calculates luminance as follows:calculates luminance as follows:

Tone-based shadingTone-based shading Shading metal ObjectsShading metal Objects

Traditional shadingTraditional shading kd = 1, ka = 0kd = 1, ka = 0 The image hides shape and material The image hides shape and material

information in the dark regions.information in the dark regions.

Traditional shadingTraditional shading Additional information can be Additional information can be

provided by highlights (direction of provided by highlights (direction of light) and edge lines (divisions).light) and edge lines (divisions).

Image produced by adjusting kd and ka

Traditional shadingTraditional shading Combining the shaded and illustrated model.Combining the shaded and illustrated model. Poor image and loss of detail, not automated.Poor image and loss of detail, not automated.

Tone-based shadingTone-based shading

Tones Tones : color scales created by adding : color scales created by adding grey to a certain color.grey to a certain color.

Tones are important to illustration, Tones are important to illustration, especially when restricted to a limited especially when restricted to a limited luminance range.luminance range.

Temperature Temperature : used to give depth cue. : used to give depth cue. Warm colors advance, cool colors recede.Warm colors advance, cool colors recede. Warm – red, orange, yellowWarm – red, orange, yellow Cool – blue, violate, and greenCool – blue, violate, and green Temperate – red-violets, red-greensTemperate – red-violets, red-greens

Tone for a pure red object: sum blue-Tone for a pure red object: sum blue-to-yellow and dark-to-red to tone.to-yellow and dark-to-red to tone.

Creating a toneCreating a tone

Tone-based shadingTone-based shading

Tone-based shadingTone-based shading

Generalize the classic shading model Generalize the classic shading model to experiment with tones using the to experiment with tones using the cosine term:cosine term:

Use blue and yellow as two Use blue and yellow as two temperature extremes:temperature extremes:

Tone-based shadingTone-based shading Combining luminance shift (traditional shading), Combining luminance shift (traditional shading),

tone and temperature based shading.tone and temperature based shading.

b = 0.4, y = 0.4,    = 0.2, and   = 0.6

Tone-based shadingTone-based shading The different values of The different values of bb and and yy determine the strength of the overall determine the strength of the overall

temperature shift, where as and determine the prominence of the temperature shift, where as and determine the prominence of the object color, and the strength of the luminance shift. object color, and the strength of the luminance shift.

b = 0.55, y = 0.3,    = 0.25, and   = 0.5

Shading of Metal ObjectsShading of Metal Objects

Technical illustrators use a different Technical illustrators use a different technique to communicate whether or technique to communicate whether or not an object is metal. not an object is metal.

Illustrators represent a metallic surface Illustrators represent a metallic surface by alternating dark and light bands. by alternating dark and light bands.

Method: map a set of twenty stripes of Method: map a set of twenty stripes of varying intensity along the parametric varying intensity along the parametric axis of maximum curvature.axis of maximum curvature.

Shading of Metal ObjectsShading of Metal Objects Phong vs metal-shadingPhong vs metal-shading

Shading of Metal ObjectsShading of Metal Objects metal-shading with edge and cool-to-warm shiftmetal-shading with edge and cool-to-warm shift

Colored ObjectsColored Objects

Conclusion:Conclusion: An automated technical illustration An automated technical illustration

method is presented using edge method is presented using edge lines, highlighting, color-shifts and lines, highlighting, color-shifts and metal-shading.metal-shading.

Future Work:Future Work: Improvements in illustration rulesImprovements in illustration rules Automate other illustration formsAutomate other illustration forms Interactive illustrationInteractive illustration

????