toonmapping

Toon mapping is a non-photorealistic rendering technique used to produce cartoon-like visuals from 2D images or 3D scenes. The key idea is to map a continuous spectrum of light and color into a small set of discrete shading levels and to emphasize outlines, resulting in a stylized, cell-shaded appearance.

Two core components are shading and edge rendering. Shading uses a quantization (posterization) of illumination, often via a toon ramp that outputs a limited number of brightness bands per surface, combined with a simple Lambert or specular model. Edge rendering detects boundaries between regions of different illumination or depth and draws dark contours.

Implementation: In real-time software this is commonly done in shaders: compute lighting, apply a toon mapping function to reduce levels, then overlay edge lines from depth or normal maps. Optional tweaks include rim lighting, texture blending, and dithering to reduce banding. Image-based approaches may post-process with posterization and contour extraction.

Applications and history: Toon mapping is widely used in video games, animation, and film to achieve a stylized look; it relates to cel shading and non-photorealistic rendering. Early computer graphics research in the 1990s introduced cel shading concepts; modern engines provide dedicated toon shading pipelines and materials.

See also: Cel shading, Non-photorealistic rendering, Posterization, Contour detection, Shader.