Rendered Without Cel Shading

Rendered With Cel Shading

The Basics

The core of cel-shading an image is mapping the dot product of the normal vector and the light vector (Lambertian shading) which is a value from 0 to 1 to a 1D grey-scaled image (or realistically any 1D texture). The discrete shading colours that are mapped to the 1D texture give images that hand drawn look. Further extension to cel-shading could incorporate outlining the images with black as well to further enrich the hand drawn feeling

Example of the greyscale texture used to map the lambertian shading value