Non-photorealistic rendering
Non-photorealistic rendering (NPR) is an area of
History and criticism of the term
The term non-photorealistic rendering is believed to have been coined by the SIGGRAPH 1990 papers committee, who held a session entitled "Non Photo Realistic Rendering".[1][2]
The term has received some criticism:
- The term "photorealistic rendering") and artists. For artists—who are the target consumers of NPR techniques—it refers to a school of painting that focuses on reproducing the effect of a camera lens, with all the distortion and hyper-reflections[definition needed] that it creates. For graphics researchers, however, 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 (made-up) 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 now more general term "computer graphics", with "photorealistic graphics" being the term used to describe "traditional" computer graphics.[citation needed]
- Many techniques that are used to create 'non-photorealistic' images are not rendering 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[when?] 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 "non-photorealistic" term 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,[3] running on even numbered years. From 2007 onward, NPAR began to also run on odd-numbered years, co-located with ACM SIGGRAPH.[4]
3D
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
NPR techniques for 3D images include cel shading and Gooch shading.
Many methods can be used to draw stylized outlines and strokes from 3D models, including occluding contours and Suggestive contours.[6]
For enhanced legibility, the most useful
2D
The input to a two dimensional NPR system is typically an image or video. The output is a typically an artistic rendering of that input imagery (for example in a watercolor, painterly or sketched style) although some 2D NPR serves non-artistic purposes e.g. data visualization.
The artistic rendering of images and video (often referred to as image stylization[7]) traditionally focused upon heuristic algorithms that seek to simulate the placement of brush strokes on a digital canvas.[8]
Arguably, the earliest example of 2D NPR is Paul Haeberli's 'Paint by Numbers' at SIGGRAPH 1990. This (and similar interactive techniques) 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.
Subsequently, basic image processing operations using gradient operators[9] or statistical moments[10] were used to automate this process and minimize user interaction in the late nineties (although artistic control remains with the user via setting parameters of the algorithms). This automation enabled practical application of 2D NPR to video, for the first time in the living paintings of the movie What Dreams May Come (1998).
More sophisticated image abstractions techniques were developed in the early 2000s harnessing computer vision operators e.g. image salience,[11] or segmentation[12] operators to drive stroke placement. Around this time, machine learning began to influence image stylization algorithms notably image analogy[13] that could learn to mimic the style of an existing artwork.
The advent of deep learning has re-kindled activity in image stylization, notably with neural style transfer (NST) algorithms that can mimic a wide gamut of artistic styles from single visual examples. These algorithms underpin mobile apps capable of the same e.g. Prisma
In addition to the above stylization methods, a related class of techniques in 2D NPR address the simulation of artistic media. These methods include simulating the
Artistic rendering
Artistic rendering is the application of
Notable films and games
This section lists some seminal uses of NPR techniques in films, games and software. See
Short films | ||
---|---|---|
Technological Threat | 1988 | Early use of toon shading together with Tex Avery-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 by Bob Sabiston |
Ryan | 2004 | Nonlinear projection and other distortions of 3D geometry |
The Girl Who Cried Flowers | 2008 | Watercolor-style rendering by Auryn |
Feature films | ||
What Dreams May Come | 1998 | Painterly rendering in the "painted world" sequence |
Tarzan | 1999 | First use of Disney's "Deep Canvas" system |
Waking Life | 2001 | First use of rotoshop in a feature film |
A Scanner Darkly | 2006 | "a 15-month animation process" |
Video games and other software | ||
Jet Set Radio | 2000 | Early use of toon-shading in video games |
SketchUp | 2000 | Sketch-like modelling software with toon rendering |
The Legend of Zelda: The Wind Waker | 2002 | One of the most well-known cel-shaded games |
Valkyria Chronicles | 2008 | Uses a number of NPR techniques in the game, including a sketch-like shading method |
XIII |
2003 | A game made as "comic"-like as possible |
Ōkami | 2006 | A game whose visuals emulate the style of sumi-e (Japanese ink wash painting) |
Guilty Gear Xrd | 2014 | Fighting game using cel-shaded 3D characters with limited animation to imitate the look of 2D sprites |
Vue Xstream | 2015 | 3D environment creation software featuring an NPR renderer with various traditional art style emulating presets |
Return of the Obra Dinn | 2018 | A 3D game rendered in a unique monochrome, pointillist style |
Manifold Garden | 2019 | A 3D puzzle game using impossible geometry, notable for its novel edge-shading techniques.[14]
|
References
- S2CID 12199502.[page needed]
- ^ Schofield, Simon (March 1994). Non-photorealistic rendering: a critical examination and proposed system (Thesis).
- ^ "Site officiel du Festival et du Marché international du film d'animation d'Annecy". www.annecy.org. Retrieved 20 April 2018.
- ^ "Archived copy". siggraph.org. Archived from the original on 21 December 1996. Retrieved 13 January 2022.
{{cite web}}
: CS1 maint: archived copy as title (link) - ISBN 978-1-55622-041-8.
- S2CID 52912187.
- S2CID 40656135.[page needed]
- S2CID 2656810.
- S2CID 13139308.
- S2CID 16915734.
- S2CID 9610948.
- S2CID 1146198.
- S2CID 2201072.
- S2CID 221178781.
Further reading
Some key papers in the development of NPR are:
- Haeberli, Paul (1990). "Paint by numbers: Abstract image representations". ACM SIGGRAPH Computer Graphics. 24 (4): 207–214. .
- Saito, Takafumi; Takahashi, Tokiichiro (1990). "Comprehensible rendering of 3-D shapes". ACM SIGGRAPH Computer Graphics. 24 (4): 197–206. .
- Cockshott, Malcolm Tunde (1991). Wet and Sticky: A Novel Model for Computer-Based Painting (Thesis). ProQuest 2124902248.
- Winkenbach, Georges; Salesin, David H. (1994). "Computer-generated pen-and-ink illustration". Proceedings of the 21st annual conference on Computer graphics and interactive techniques - SIGGRAPH '94. pp. 91–100. S2CID 3234749.
- Salisbury, Michael P.; Anderson, Sean E.; Barzel, Ronen; Salesin, David H. (1994). "Interactive pen-and-ink illustration". Proceedings of the 21st annual conference on Computer graphics and interactive techniques - SIGGRAPH '94. pp. 101–108. S2CID 1098501.
- Meier, Barbara J. (1996). "Painterly rendering for animation". Proceedings of the 23rd annual conference on Computer graphics and interactive techniques - SIGGRAPH '96. pp. 477–484. S2CID 1199189.
- Gooch, Amy; Gooch, Bruce; Shirley, Peter; Cohen, Elaine (1998). "A non-photorealistic lighting model for automatic technical illustration". Proceedings of the 25th annual conference on Computer graphics and interactive techniques - SIGGRAPH '98. pp. 447–452. S2CID 1411270.