Tooncurves

Tooncurves is a term used in digital animation and non-photorealistic rendering to describe curve-based mapping tools that shape toon shading and edge styles. In practice, a tooncurve maps input tonal values (luminance or color channels) through a bezier or polyline curve to produce stylized, flat regions of color and discrete tonal bands.

Implemented as a curve or color ramp in node-based shading systems, tooncurves let artists control how light and color are quantized. Users place control points, adjust tangents, choose interpolation, and define input and output ranges. Some pipelines separate luminance to a toon curve for shading and use a second curve to drive edge lines by thresholding or contour detection.

Common uses include cel shading, posterization for a cartoon look, and maintaining consistent lighting across frames in animation. They are often used together with edge-detection to generate outlines around objects, helping to define form in a stylized way.

Origins and terminology vary; tooncurves is not a formally standardized term, but an informal label for curve-based toon shading controls found in many tools and tutorials. The concept reflects a broader practice of mapping continuous image data through curves to achieve deliberate, cartoon-like aesthetics.

See also: Non-photorealistic rendering, cel shading, color ramp, edge detection.