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Cel shading

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Object with a basic cel-shader (AKA "toon shader") and border detection.

Cel-shaded animation (also called "cel-shading", "cell-shading", or "toon shading") is a type of non-photorealistic rendering designed to make computer graphics appear to be hand-drawn. Cel-shading, short for celluloid shading, is often used to mimic the style of a comic book or cartoon. It is a relatively 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 taking the first syllable of celluloid, a thermoplastic made of nitrocellulose and camphor.

Process

Hand-drawn animation

Main article: Traditional animation

In hand-drawn animation or traditional animation, from the mid-19th century onwards, artists would start by creating pencil drawings; these would then be transferred onto celluloid, made of cellulose nitrate, either by using xerography (a photocopying technique) and paint, or ink and paint. Later, by the mid-20th century, celluloid was made using cellulose acetate instead of cellulose nitrate due to the latter burning easily and suffering from spontaneous decomposition, albeit the process remained the same.

Digital animation

The cel-shading process starts with 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 color 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.

History

Video games
File:Zelda wind waker.jpg
An example of cel-shading from The Legend of Zelda: The Wind Waker.

The first video game to specifically feature cel-shading as its primary animation style was Fear Effect for the Sony PlayStation, which was released in the year 2000. Later in the same year, Jet Set Radio was released in Japan for the Sega Dreamcast. Though its sales in the Japanese market were relatively low, the game fared better in the US under the title Jet Grind Radio. As a result, it has been credited with increasing the popularity of cel-shading in the video game industry, as many developers began to implement the technique shortly after the game's American debut. ("Jet Grind Radio's cell-shading technology will undoubtedly be one of the most frequently imitated graphical trends of the next few years." [1])

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, Klonoa 2, the Viewtiful Joe series, and XIII were released with positive feedback, though none were considered blockbusters in terms of sales figures. 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 and Sly 2: Band of Thieves.

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 and upcoming examples include Dragon Quest VIII, Killer 7 and Metal Gear Acid 2.

Examples of digital cel-shading

Main article: List of cel-shaded video games

Some of the more prominent films that have featured cel-shaded graphics are:

The Tachikoma Days sequences at the end of the episodes are entirely CG using cel-shading.

Some of the more prominent games that have featured cel-shaded graphics are:

See also

Other types of animation

References

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