Non-photorealistic rendering
Encyclopedia
Non-Photorealistic rendering (NPR) is an area of computer graphics
that focuses on enabling a wide variety of expressive styles for digital art. In contrast to traditional computer graphics
, which has focused on photorealism
, NPR is inspired by artistic styles such as painting
, drawing
, technical illustration
, and animated cartoons. NPR has appeared in movies
and video games in the form of "toon shading", as well as in scientific visualization
, architectural illustration and experimental animation. An example of a modern use of this method is that of cel-shaded animation
.
The first conference on Non-Photorealistic Animation and Rendering included a discussion of possible alternative names. Among those suggested were "expressive graphics", "artistic rendering", "non-realistic graphics", "art-based rendering", and "psychographics". All of these terms have been used in various research papers on the topic, but the term NPR seems to have nonetheless taken hold.
The first technical meeting dedicated to NPR was the ACM sponsored Symposium on Non-Photorealistic Rendering and Animation (NPAR) in 2000. NPAR is traditionally co-located with the Annecy Animated Film Festival, running on even numbered years. From 2007 NPAR began to also run on odd-numbered years, co-located with ACM SIGGRAPH.
Three-dimensional NPR is the style that is most commonly seen in video games and movies. The output from this technique is almost always a 3D model
that has been modified from the original input model to portray a new artistic style. In many cases, the geometry
of the model is identical to the original geometry, and only the material applied to the surface is modified. With increased availability of programmable GPU's, shaders have allowed NPR effects to be applied to the rasterised image that is to be displayed to the screen. The majority of NPR techniques applied to 3D geometry are intended to make the scene appear two-dimensional.
For enhanced legibility, the most useful illustrations in technical illustrations
are not necessarily photorealistic. Non-photorealistic renderings, such as exploded view
diagrams, greatly assist in showing placement of parts in a complex system.
, or pen and ink drawing.
Users who are interested in having much more control in the NPR process may be more interested in interactive techniques. Many of these NPR systems provide the user with a canvas that they can "paint" on using the cursor — as the user paints, a stylized version of the image is revealed on the canvas. This is especially useful for people who want to simulate different sizes of brush strokes according to different areas of the image.
In contrast to the methods mentioned previously, another technique in NPR is simulating the painter's medium. Methods include simulating the diffusion
of ink through different kinds of paper
, and also of pigment
s through water for simulation of watercolor.
for a list of uses of toon-shading in games and movies.
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
that focuses on enabling a wide variety of expressive styles for digital art. In contrast to traditional computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
, which has focused on photorealism
Photorealism
Photorealism is the genre of painting based on using the camera and photographs to gather information and then from this information creating a painting that appears photographic...
, NPR is inspired by artistic styles such as painting
Painting
Painting is the practice of applying paint, pigment, color or other medium to a surface . The application of the medium is commonly applied to the base with a brush but other objects can be used. In art, the term painting describes both the act and the result of the action. However, painting is...
, drawing
Drawing
Drawing is a form of visual art that makes use of any number of drawing instruments to mark a two-dimensional medium. Common instruments include graphite pencils, pen and ink, inked brushes, wax color pencils, crayons, charcoal, chalk, pastels, markers, styluses, and various metals .An artist who...
, technical illustration
Technical illustration
Technical Illustration is the use of illustration to visually communicate information of a technical nature. Technical illustrations can be components of technical drawings or diagrams...
, and animated cartoons. NPR has appeared in movies
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
and video games in the form of "toon shading", as well as in scientific visualization
Scientific visualization
Scientific visualization is an interdisciplinary branch of science according to Friendly "primarily concerned with the visualization of three-dimensional phenomena , where the emphasis is on realistic renderings of volumes, surfaces, illumination sources, and so forth, perhaps...
, architectural illustration and experimental animation. An example of a modern use of this method is that of cel-shaded animation
Cel-shaded animation
Cel-shaded animation is a type of non-photorealistic rendering designed to make computer graphics appear to be hand-drawn. Cel-shading is often used to mimic the style of a comic book or cartoon. It is a somewhat recent addition to computer graphics, most commonly turning up in video games...
.
History
The term "non-photorealistic rendering" was probably coined by David Salesin and Georges Winkenbach in a 1994 paper. Many researchers find the terminology to be unsatisfying; some of the criticisms are as follows:- The term "photorealismPhotorealismPhotorealism is the genre of painting based on using the camera and photographs to gather information and then from this information creating a painting that appears photographic...
" means something different to graphics researchers than it does to artists, who are the target consumers of NPR techniques. For artists, it refers to a school of painting that focuses on reproducing the effect of a camera lens, with all the distortion and hyper-reflections that involves. For graphics researchers, it refers to an image that is visually indistinguishable from reality. In fact, graphics researchers lump the kinds of visual distortions that are used by photorealist painters into non-photorealism. - Describing something by what it is not is problematic. Equivalent comparisons might be "non-elephant biology", or "non-geometric mathematics". NPR researchers have stated that they expect the term will disappear eventually, and be replaced by the more general term "computer graphics", with "photorealistic graphics" being used to describe traditional computer graphics.
- Many techniques that are used to create 'non-photorealistic' images are not renderingRendering (computer graphics)Rendering is the process of generating an image from a model , by means of computer programs. A scene file contains objects in a strictly defined language or data structure; it would contain geometry, viewpoint, texture, lighting, and shading information as a description of the virtual scene...
techniques. They are modelling techniques, or post-processing techniques. While the latter are coming to be known as 'image-based rendering', sketch-based modelling techniques, cannot technically be included under this heading, which is very inconvenient for conference organisers.
The first conference on Non-Photorealistic Animation and Rendering included a discussion of possible alternative names. Among those suggested were "expressive graphics", "artistic rendering", "non-realistic graphics", "art-based rendering", and "psychographics". All of these terms have been used in various research papers on the topic, but the term NPR seems to have nonetheless taken hold.
The first technical meeting dedicated to NPR was the ACM sponsored Symposium on Non-Photorealistic Rendering and Animation (NPAR) in 2000. NPAR is traditionally co-located with the Annecy Animated Film Festival, running on even numbered years. From 2007 NPAR began to also run on odd-numbered years, co-located with ACM SIGGRAPH.
3D
Polygonal modeling
In 3D computer graphics, polygonal modeling is an approach for modeling objects by representing or approximating their surfaces using polygons. Polygonal modeling is well suited to scanline rendering and is therefore the method of choice for real-time computer graphics...
that has been modified from the original input model to portray a new artistic style. In many cases, the geometry
Solid geometry
In mathematics, solid geometry was the traditional name for the geometry of three-dimensional Euclidean space — for practical purposes the kind of space we live in. It was developed following the development of plane geometry...
of the model is identical to the original geometry, and only the material applied to the surface is modified. With increased availability of programmable GPU's, shaders have allowed NPR effects to be applied to the rasterised image that is to be displayed to the screen. The majority of NPR techniques applied to 3D geometry are intended to make the scene appear two-dimensional.
For enhanced legibility, the most useful illustrations in technical illustrations
Technical communication
Technical communication is a method of researching and creating information about technical processes or products directed to an audience through media. The information must be relevant to the intended audience. Technical communicators often work collaboratively to create products for various...
are not necessarily photorealistic. Non-photorealistic renderings, such as exploded view
Exploded view
An exploded view drawing is a diagram, picture or technical drawing of an object, that shows the relationship or order of assembly of various parts....
diagrams, greatly assist in showing placement of parts in a complex system.
2D
The input to a two-dimensional NPR system is most commonly an image; however, there are systems that take 3D geometry information as input and produce a 2D image or video as output. Again, many of the systems are intended to mimic a desired artistic style, such as watercolor, impressionismImpressionism
Impressionism was a 19th-century art movement that originated with a group of Paris-based artists whose independent exhibitions brought them to prominence during the 1870s and 1880s...
, or pen and ink drawing.
Users who are interested in having much more control in the NPR process may be more interested in interactive techniques. Many of these NPR systems provide the user with a canvas that they can "paint" on using the cursor — as the user paints, a stylized version of the image is revealed on the canvas. This is especially useful for people who want to simulate different sizes of brush strokes according to different areas of the image.
In contrast to the methods mentioned previously, another technique in NPR is simulating the painter's medium. Methods include simulating the diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
of ink through different kinds of paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
, and also of pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s through water for simulation of watercolor.
Notable films and softwares
This section lists some seminal uses of NPR techniques in films and software. See the article on cel-shaded animationCel-shaded animation
Cel-shaded animation is a type of non-photorealistic rendering designed to make computer graphics appear to be hand-drawn. Cel-shading is often used to mimic the style of a comic book or cartoon. It is a somewhat recent addition to computer graphics, most commonly turning up in video games...
for a list of uses of toon-shading in games and movies.
| Short films | ||
|---|---|---|
| Technological Threat | 1988 | Early use of toon shading together with Tex Avery Tex Avery Frederick Bean "Fred/Tex" Avery was an American animator, cartoonist, voice actor and director, famous for producing animated cartoons during The Golden Age of Hollywood animation. He did his most significant work for the Warner Bros... -style cartoon characters. |
| Gas Planet | 1992 | Pencil-sketching 3D rendering by Eric Darnell. |
| Fishing | 2000 | Watercolor-style 3D rendering David Gainey. |
| RoadHead Snack and Drink |
1998 1999 |
Short films created with Rotoshop Rotoshop Rotoshop is a proprietary graphics editing program created by Bob Sabiston.Rotoshop uses an animation technique called interpolated rotoscoping, which has been used in Richard Linklater's films Waking Life and A Scanner Darkly, as well as the Talk to Chuck advertising campaign for Charles Schwab.... by Bob Sabiston. |
| Ryan Ryan (film) Ryan is a 2004 animated documentary by Chris Landreth about the Canadian animator Ryan Larkin, who in later years lived on skid row in Montreal following a history of drug and alcohol abuse.... |
2004 | Nonlinear projection and other distortions of 3D geometry. |
| Feature films | ||
| What Dreams May Come What Dreams May Come (film) What Dreams May Come is a 1998 American supernatural drama film, starring Robin Williams, Cuba Gooding, Jr., and Annabella Sciorra. The film is based on the 1978 novel of the same name by Richard Matheson, and was directed by Vincent Ward. The title is taken from a line in Hamlet's To be, or not to... |
1998 | Painterly rendering in the "painted world" sequence. |
| Tarzan Tarzan (1999 film) Tarzan is a 1999 American animated feature film produced by Walt Disney Feature Animation and released by Walt Disney Pictures on June 18, 1999... |
1999 | First use of Disney's "Deep Canvas" system. |
| Waking Life Waking Life Waking Life is an American animated film , directed by Richard Linklater and released in 2001. The entire film was shot using digital video and then a team of artists using computers drew stylized lines and colors over each frame.The film focuses on the nature of dreams, consciousness, and... |
2001 | First use of rotoshop in a feature film. |
| Video games and other software | ||
| Jet Set Radio Jet Set Radio is a video game for the Dreamcast, developed by Smilebit and published by Sega on June 29, 2000. A 2D version of the game was later released for Game Boy Advance; this version was developed by Vicarious Visions and published by THQ. Its sequel, Jet Set Radio Future was released 2 years later for... |
2000 | Early use of toon-shading in video games. |
| SketchUp SketchUp SketchUp is a 3D modeling program marketed by Google and designed for architectural, civil, and mechanical engineers as well as filmmakers, game developers,... |
2000 | Sketch-like modelling software with toon rendering. |
| The Legend of Zelda: The Wind Waker The Legend of Zelda: The Wind Waker The Legend of Zelda: The Wind Waker, released as in Japan, is an action-adventure game and the tenth installment in The Legend of Zelda series. It was released for the Nintendo GameCube in Japan on December 13, 2002, in North America on March 24, 2003, in Europe on May 2, 2003, and in Australia on... |
2002 | One of the most well-known cel-shaded games ever and the most controversial |
Further reading
Some key papers in the development of NPR are:- "Paint by Numbers: Abstract Image Representations", by Paul HaeberliPaul HaeberliPaul E. Haeberli is an American computer graphics programmer and researcher.Paul Haeberli studied for a Bachelor of Science degree in Electrical Engineering at the University of Wisconsin–Madison, USA....
, SIGGRAPHSIGGRAPHSIGGRAPH is the name of the annual conference on computer graphics convened by the ACM SIGGRAPH organization. The first SIGGRAPH conference was in 1974. The conference is attended by tens of thousands of computer professionals...
90 - "Comprehensible rendering of 3-D shapes", by Saito and Takahashi, SIGGRAPH 90
- "Wet and Sticky: A Novel Model for Computer-Based Painting", by Tunde Cockshott, PhD Thesis, Glasgow University, 1991
- "Computer-Generated Pen-and-Ink Illustration", by Winkenbach and Salesin, SIGGRAPH 94
- "Interactive Pen-and-Ink Illustration", by Salisbury, Anderson, Barzel, Salesin, SIGGRAPH 94
- "Painterly Rendering for Animation", by Barb Meier, SIGGRAPH 96
- "A Non-Photorealistic Lighting Model For Automatic Technical Illustration", by Amy Gooch, Bruce Gooch, Peter Shirley.Elaine Cohen, SIGGRAPHSIGGRAPHSIGGRAPH is the name of the annual conference on computer graphics convened by the ACM SIGGRAPH organization. The first SIGGRAPH conference was in 1974. The conference is attended by tens of thousands of computer professionals...
98