Cel-Shading

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. The difference occurs when a cel-shaded object is drawn on-screen. The rendering engine only selects a few shades of each colour for the object, producing a flat look. This is not the same as using only a few shades of texture for an object, as lighting and other environmental factors would come into play and ruin the effect. Therefore, cel-shading is often implemented as an additional rendering pass after all other rendering operations are completed.

In order to draw black ink lines outlining an object's contours, the back-face culling is inverted to draw back-faced triangles with black-coloured vertices. The vertices must be drawn multiple times with a slight change in translation to make the lines "thick." This produces a black-shaded silhouette. The back-face culling is then 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 even contours that reside inside the object's surface in screen space.

Video games
The first 3D video game to feature true real-time cel shading was Jet Set 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 with an outline effect some mistake for cel shading, but it in-fact, still used traditional shading techniques. The are several other games, such as Megaman Legends, that used static cel-shaded textures (without realtime 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 Cloud 2, Cel Damage, Klonoa 2, 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 The Legend of Zelda: The Wind Waker, Sly 2: Band of Thieves'', and Tales of Symphonia.

Originally, Sega’s The House of the Dead III for the 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 favour 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 not realistically powerful enough to render a fully 3D world have made use of cel shading, for example, the Tony Hawk games for 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, Killer7, Metal Gear Acid 2, and Ōkami.

Examples of digital cel-shading
Some of the more prominent games that have featured cel-shaded graphics:
 * Auto Modellista
 * Bomberman Generation
 * Bomberman Jetters
 * Breath of Fire: Dragon Quarter
 * Cel Damage
 * Crackdown
 * ''Crazyracing Kartrider
 * Dark Cloud 2
 * Dragon Ball Z Budokai series
 * Dragon Quest VIII
 * Dragon Quest IX
 * Dragon Quest Monsters Joker
 * Fire Emblem: Path of Radiance
 * Freespace 2 Open (the option is still a work-in-progress)
 * Gekitou Pro Yakyuu
 * Gungrave series
 * Harvest Moon: Save the Homeland
 * Jackie Chan Adventures
 * Jet Set Radio
 * Jet Set Radio Future
 * Killer7
 * Klonoa 2
 * The Legend of Zelda: Phantom Hourglass
 * The Legend of Zelda: The Wind Waker
 * The Legend of Zelda: Twilight Princess
 * Mega Man X7
 * Mega Man X Command Mission
 * Metal Gear Acid 2
 * Monster Rancher 3
 * Naruto video games
 * Ōkami
 * Robotech: Battlecry
 * Rogue Galaxy
 * ''Runaway: A Road Adventure
 * Shin Megami Tensei III: Nocturne
 * ''Shin Megami Tensei: Digital Devil Saga and Digital Devil Saga 2
 * Silverfall
 * Sly Cooper series
 * ''Sonic Shuffle
 * ''Super Mario Sunshine
 * ''Ultimate Spider-Man
 * Tales of Symphonia
 * Tony Hawk's American Sk8land
 * Viewtiful Joe series
 * Wacky Races for Dreamcast
 * Wild Arms 3
 * XIII
 * X-Men Legends II: Rise of Apocalypse
 * Zone of the Enders: The 2nd Runner

Similar technology
Interpolated rotoscoping can be used to create the effects of hand-drawn animation, but the source material do not need to be computer generated. In addition, rotoscoping apply effects on already produced video, while cel-shading effects are applied when the object is displayed.