Cel-shaded animation

Cel-shaded animation (also called cel-shading or toon shading) 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 console video games. Though the end result of cel-shading has a very simplistic feel like that of hand-drawn animation, the process is complex. The name comes from the clear sheets of acetate, called cels, that are painted on for use in traditional 2D animation, such as Disney classics.

Process

The cel-shading process starts with a typical 3D model. Where cel-shading differs from conventional rendering is in its use of non-photorealistic lighting. Conventional (smooth) lighting values are calculated for each pixel and then mapped to a small number of discrete shades to create the characteristic flat look.

Black "ink" outlines and contour lines can be created using a variety of methods. One popular method is to first render a black silhouette, slightly larger than the object itself. Backface culling is inverted and the back-facing triangles are drawn in black. To dilate the silhouette, these back-faces may be drawn in wireframe multiple times with slight changes in translation. Alternately, back-faces may be rendered solid-filled, with their vertices translated along their vertex normals in a vertex shader. After drawing the silhouette, back-face culling is set back to normal to draw the shading and optional textures of the object. Finally, the image is composited via Z-buffering, as the back-faces always lie deeper in the scene than the front-faces. The result is that the object is drawn with a black outline and interior contour lines.

The Utah teapot rendered using cel-shading:

# The back faces are drawn with thick lines
# The object is drawn with a basic texture
# Shading

Steps 2 and 3 can be combined using multi-texturing (see texture mapping).

Another outlining technique is to use 2D image-processing. First, the scene is rendered (with cel-shading) to a screen-sized color texture:

Then, the scene's depth and world-space surface normal information are rendered to screen-sized textures:

A Sobel filter or similar edge-detection filter is applied to the normal/depth textures to generate an edge texture. Texels on detected edges are black, while all other texels are white:

Finally, the edge texture and the color texture are composited to produce the final rendered

As with most image-processing techniques, the performance penalty for this method is not affected by scene complexity.

History

Video games

The first 3D video game to feature true real-time cel-shading was "Jet Grind Radio" (2000) for the Sega Dreamcast. Another game, "Fear Effect" for the Sony PlayStation, was released in 2000 and was noted for its use of dramatic textures to give an anime appearance to its characters, but lacked outlines and dynamic light-sourcing. Games before "Fear Effect" have used textures in a similar fashion, but not as starkly apparent or stylized as the game. "Wacky Races", released on Dreamcast a few months before "Jet Set Radio", featured an outline effect often mistaken for cel-shading, but the game actually used traditional shading techniques. There are several other games, such as "Megaman Legends", that used static cel-shaded textures (without real-time lighting) in the same vein as Fear Effect created before the previous examples, but the effect created was not as strongly noticeable as the previous examples.

In the years following "Jet Set Radio", numerous other cel-shaded games were introduced during a minor fad involving cel-shaded graphics, yet only a few would fully match or surpass its mainstream appeal. The next games with cel-shading to capture the industry's attention in some form were 2002's "Jet Set Radio Future" and "Sly Cooper and the Thievius Raccoonus". Over time, more cel-shaded titles such as "Dark Chronicle", "Cel Damage", ', the "Viewtiful Joe" series, and "XIII" were released with positive feedback, though none were considered blockbusters in terms of sales figures. Originally the only cel-shaded games to receive both positive ratings and sales after "Sly Cooper and the Thievius Raccoonus" were ', "", and "Tales of Symphonia".

Originally, "The House of the Dead III" ("HotD3") for the Microsoft Xbox was cel-shaded. Early in "HotD3"’s development Sega released screenshots of the then current cel-shaded graphics to the gaming community. Shortly after those initial screenshots were released, Sega announced that they were dropping the cel-shaded graphics in favor of conventional graphic techniques. There are several suspected reasons for Sega's change of heart, the most popular and most likely is that the screenshots met much negative response from gamers who disliked the cel-shaded graphical style. Many gamers claimed the cel-shading was used purely as a gimmick in an attempt to sell more games. "HotD3" was a bloody, gory and very violent light gun game which featured zombies and other mutated and deformed creatures. Many felt the cel-shaded look clashed greatly with the game's themes and content.

More recently, handheld consoles, previously not realistically powerful enough to render a fully 3D world, have made use of cel-shading. Most notable is the Tony Hawk series and "" on the Nintendo DS.

The use of cel-shading in video games has slowed somewhat since its inception, but the technique continues to be employed in the modern era. Recent examples include "Dragon Quest VIII", "Rogue Galaxy", "Killer 7", "No More Heroes", "Metal Gear Acid 2", and "Ōkami".

List of cel-shaded media

Video games

Some of the more prominent games that have featured cel-shaded graphics:
* ".hack//G.U." series
* "Auto Modellista"
* "
* "Bleach" video games
* "Bomberman Generation"
* "Bomberman Jetters"
* ""
* "Cel Damage"
* "Crackdown"
* "Crazyracing Kartrider
* "Dark Cloud 2"
* "Dragon Ball Z Budokai series"
* "Dragon Quest VIII"
* "Dragon Quest IX"
* "Dragon Quest Monsters Joker"
* "Drift City"
* "Eternal Sonata"
* "Fear Effect"
* ""
* ""
* ""
* "FreeSpace 2 Open (the option is still a work-in-progress)"
* "Futurama (video game)"
* "Gekitou Pro Yakyuu"
* "Gungrave" series
* ""
* "Jackie Chan Adventures"
* "Jet Set Radio"
* "Jet Set Radio Future"
* ""
* "Killer7"
* "Klonoa 2"
* ""
* ""
* "Lemmingball Z"
* "Megaman Network Transmission"
* "Mega Man X7"
* "Mega Man X Command Mission"
* "Metal Gear Acid 2"
* "Mirror's Edge"
* "Monster Rancher 3"
* "
* "Naruto" video games
* "No More Heroes
* "Ōkami"
* ""
* ""
* "" (in development)
* Radilgy
* ""
* "Rogue Galaxy"
* "
* "Samurai Legend Musashi
* ""
* " and
* "Silverfall"
* "The Simpsons Game"
* "Sly Cooper" series
* "Sonic Shuffle
* "Street Fighter IV" (in development)
* "Ultimate Spider-Man
* "Tales of Symphonia"
* "Tales of Vesperia"
* "Tony Hawk's American Sk8land"
* "Viewtiful Joe" series
* "Wacky Races for Dreamcast"
* "War§ow"
* "Wild Arms 3"
* "XIII"
* ""
*
* ""

Film and television

In addition, many prominent movies, television programs, and commercials also use cel-shading:
*"Appleseed"
*"Armitage Dual-Matrix"
*"Atomic Betty"
*""
*"Bakugan Battle Brawlers"
*""
*"Canada's Worst Driver"
*"Class of the Titans"
*"Daily Planet" (2005-2006 season)
*"Delilah and Julius"
*"D.I.C.E."
*"Digimon Savers"
*"Dinosaur King"
*""
*"Dragon Booster"
*"Duck Dodgers"
*"Fairly OddParents"
*""
*""
*"Freedom Project"
*"Funky Cops"
*""
*"Futurama"
*"Galactik Football"
*""
*""
*""
*"Handy Manny"
*"He-Man and the Masters of the Universe"
*""
*"Hot Wheels Highway 35 World Race"
*"Idaten Jump"
*""
*"Invader Zim"
*"Iron Giant"
*"Justice League"
*"Kappa Mikey"
*"Kim Possible"
*""
*"Legion of Super Heroes"
*"Lego Exo-Force"
*"Loonatics Unleashed"
*"Macross Frontier"
*"MegaMan NT Warrior"
*"Mobile Suit Gundam 00"
*"Mobile Suit Gundam SEED"
*"Mobile Suit Gundam SEED Destiny"
*"Monster House"
*"Ōban Star-Racers"
*"One Piece"
*"Osmosis Jones"
*"Paprika"
*"Pokemon Battle Frontier" (Nosepass)
*""
*"" (Combee)
*""
*"Renaissance
*"Rugrats Go Wild"
*"Silver Surfer
*"Skyland"
*"Sonic X"
*""
*""
*""
*"Steamboy"
*"Storm Hawks"
*""
*"Superior Defender Gundam Force"
*""
*"Team Galaxy"
*"The Iron Giant"
*"The Littlest Robo"
*"The Simpsons" (season 19+)
*"The Simpsons Movie"
*"Titan A.E."
*""
*""
*"Transformers Cybertron"
*"Transformers Energon"
*"Treasure Planet"
*"Vexille"
*"Winx Club"
*"Zoids"

Commercials

*2008 "Scion xD" Little Deviants
*2009 "Dodge Journey"
*"Boogie"
*BP Connect 2007 ad's
*"AREVA"
*"Blockbuster" Total Access
*"Commit" mint lozenges
*"Cartoon Network Master Control"
*"HSBC" HSBCdirect.com
*"Hewlett Packard xw8400 Workstation" Titans of iron
*"Mr. Clean"
*"Pampers Kandoo" Flushable Toilet Wipes, Foaming Handsoap
*"Post Cereals" Fruity Pebbles cereal (Bowling for Fruity Pebbles ad)
*"Lego Exo-Force"
*"L’Oréal" Couleur Expert
*"Lunchables Pizza" (Atlantis Paradise Island promotion ad)
*"McCain's Zwak Punch"
*"Neopets" virtual prize code (Canadian Betty Crocker fruit-flavored snacks promotional ad)
*"Oscar Mayer Lunchables" Chicken Dunks (airhead mysteries ad)
*"Sola"/"Nero"/"Vena"/"Olera"/"Zonte" sparkling wine
*"Toyo Tires" Versado LX all-season touring tires (OK Tire promotional ad)

imilar technology

Interpolated rotoscoping can be used to create a similar effect, but the source material does not need to be computer generated. In addition, rotoscoping is applied to an existing image, whereas cel-shading is applied during the generation of the image.

ee also

*Traditional animation
*Special effects animation
*Character animation
*Computer animation and 3D computer graphics
*Skeletal animation
*Non-photorealistic rendering

References

* [http://www.celshading.com/ CelShading.com] . More information on 3D cel-shading including an image gallery.
* [http://www.celshader.com/FAQ.html Celshader.com FAQ] . Retrieved August 2, 2005.
* [http://dreamcast.ign.com/articles/163/163512p1.html IGN: Jet Grind Radio Review] . Retrieved August 4, 2005.
* [http://www.gamedev.net/reference/articles/article1438.asp GameDev.net - Cel-Shading] . Retrieved August 5, 2005.