Stylized Depiction in Computer Graphics
Non-Photorealistic, Painterly and 'Toon Rendering

an annotated survey of online resources
by Craig Reynolds

The 3rd International Symposium on Non-Photorealistic Animation and Rendering
NPAR 2004
June 7-9, 2004 in Annecy, France
Paper submission deadline: October 23, 2003

Sections within this page
Investigations of specific techniques Relating to the field as a whole
Painterly Rendering
Sketching, Pen-and-Ink, Engraving
Stylized Depiction to Enhance Legibility
Other Rendering Styles
Stylized Halftoning
Real Time Techniques
Interactive Techniques
3D Modeling Based on 2D Sketch Input
Toon Shaders/Plug-Ins
Painterly Image Processing Techniques
Simulation of Traditional Artistic Media
Non-traditional perspective
Stylized Motion and its Depiction
Scientific Visualization
3D Effects for Traditional2D Cel Animation
Surveys and Overview Articles
Conferences and Conference Sessions
Research Groups and Project Pages
Interactive Entertainment

While I have not done research in this area myself, I am fascinated by the computer graphic technique known as non-photorealistic rendering. (Admittedly it is a little odd to name a field of study by what it is not. Stanislaw Ulam apparently once remarked: "The study of non-linear physics is like the study of non-elephant biology.") My list of links on this topic began to outgrow its place on my bookmarks list, so I created this page to give them a home, and perhaps to help other people interested in the field.

To better describe the kinds of techniques listed here, and to define the informal taxonomy used on this page, it is helpful to note that techniques for stylized depiction can be classified along the axis from interactive to fully automatic, and that there are three distinct types of input for these stylized depiction processes:

  1. 3D scenes (described in terms of geometry, color, lighting, etc.) for rendering
  2. images for processing
  3. brushstrokes from a user (like the input to a paint system)

In computer graphics, photorealistic rendering attempts to make artificial images of simulated 3d environments that look "just like the real world." So non-photorealistic rendering (NPR) is any technique that produces images of simulated 3d world in a style other than realism. Often these styles are reminiscent of paintings (painterly rendering), or of various other styles of artistic illustration (sketch, pen and ink, etching, lithograph, ...) Of particular commercial interest are techniques that can render 3d scenes in styles which match the "look" of traditionally animated films. Often called 'toon shading, these techniques allow for seamless combination of 3d elements with traditional cel animation.

Another important application of non-photorealistic rendering is to help the user understand that a depiction is only approximate. Psychologically, photorealistic rendering seems to imply an exactness and perfection which may overstate the fidelity of the simulated scene to a real object. The Piranesi system (mentioned below) has proved more useful than photorealistic rendering in an application that pre-visualizes kitchen remodeling. The Teddy modeler (see below) uses a sketchy rendering style to suggest the approximate 3D shapes it has inferred from the user's 2d drawing.

Also listed here are some image processing techniques which can transform an image into a style that suggests a painting or other artistic styles. The images can be photographic or from any other source. Some of the techniques have the ability to process a series of images, as from a video or film camera, and to produce a stylized image that remains stable from frame to frame, allowing the creation of something like an "animated painting."

This page also includes: (1) some computational techniques that carefully simulate traditional artistic media such as watercolor and ink painting, (2) some references to work on non-traditional perspective common to traditional illustration but rare in computer graphics, (3) techniques for finding and using silhouettes of 3D objects, (4) non-realistic techniques designed for real time or interactive rates, and (5) non-traditional halftones and screenings.

Finally it should be noted that any claim that an automatic process can produce "art" or a "painting" should be regarded as suspect. Making art is a creative and thoughtful process. It may even be uniquely human. The possibility of artificial creativity, let alone artificial intelligence, are open research questions. None of the techniques described here are candidates for true artificial creativity. I have tried to use neutral language ("...suggests a painterly style...") on this page to skirt the distinction between art and procedural techniques for stylized depiction.

(Note: items marked [new] have been added in the three months prior to the time of the "last update" indicated at the bottom of this page.)

Meier haystack
© 1996 Barbara J. Meier
Painterly Rendering
Curtis: New Chair
© 1998 Cassidy Curtis
Hamel castle
© 1998 Jörg Hamel

Sketching, Pen-and-Ink, Engraving (and related high-contrast rendering styles)
Gooch automatic technical illustration
© 1998 Gooch, Gooch, Shirley & Cohen

Stylized Depiction to Enhance Legibility
Kowalski (et al.): rendered a la Seuss
© 1999 Kowalski et al.
Other Rendering Styles Stylized Halftoning
Hertzman realtime self portrait
© 1999 Aaron Hertzmann

Real Time Techniques (or at least, those running at interactive rates)
Piranesi Guggenhiem by Kyoto Institute of Technology
created with Piranesi
by Kyoto Institute of Technology
Interactive Techniques 3D Modeling Based on 2D Sketch Input Toon Shaders/Plug-Ins (and related "cel-look" effects)
Cabral/Leedom LIC Amphitheater
© 1993 Cabral and Leedom
(RE:Vision) Conservatory as oil painting
© 1999 RE:Vision Effects
Hertzman tomatoes as oil painting
© 1998 Aaron Hertzmann

Painterly Image Processing Techniques
Strassmann shrimp
© 1986 Steve Strassmann

Simulation of Traditional Artistic Media Silhouettes Non-traditional perspective (for viewing and modeling) Stylized Motion and its Depiction
Kirby (et al.): flow visualization
© 1999 Kirby, Marmanis and Laidlaw
Scientific Visualization Computer Graphic Effects for Traditional Cel Animation Books Surveys and Overview Articles Miscellaneous Not yet categorized

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visitors since June 27, 1999
Last update: September 22, 2003