Cel-shaded animation or cel-shading is the art of turning computer graphics into cartoon and comic book style art and attempting to mimic a more stylistic cartoon style, such as charcoal, watercolors or etching. Cel-shading is a sharp contrast to photorealistic graphics. 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 simple and retro feel, reminiscent of older hand drawn animation, the process is complex.
Process
The cel-shading process starts with typical 3D modelling under the hood. The difference occurs when a cel-shaded object is drawn onscreen. 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 the 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 either 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. Z-buffering does the magic because the back-faces always lie deeper in the scene than the front-faces, so the result is the object drawn with black outlines, even contours that reside inside the object's surface in screen space.
Appearances
Cel-shaded art has appeared in the following places: