Cel shading or toon shading is a type of non-photorealistic rendering designed to make 3-D computer graphics appear to be flat by using less shading color instead of a shade gradient or tints and shades. A cel shader is often used to mimic the style of a comic book or cartoon and/or give the render a characteristic paper-like texture. There are similar techniques that can make an image look like a sketch, an oil painting or an ink painting. The name comes from cels, clear sheets of acetate which were painted on for use in traditional 2D animation.
A representation of a spacesuit from The Adventures of Tintin comic Explorers on the Moon with a basic cel shader (also known as a toon shader) and border detection
Non-photorealistic rendering
Non-photorealistic rendering (NPR) is an area of computer graphics that focuses on enabling a wide variety of expressive styles for digital art, in contrast to traditional computer graphics, which focuses on photorealism. NPR is inspired by other artistic modes such as painting, drawing, technical illustration, and animated cartoons. NPR has appeared in movies and video games in the form of cel-shaded animation as well as in scientific visualization, architectural illustration and experimental animation.
A normal shader (left) and an NPR shader using cel-shading (right)
A non-photorealistic rendering of an existing 2D (photographic) image
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