Shading uses a fudge factor (ambient lighting intensity) to make it more "natural", since it is next to impossible to account for all light sources affecting the image.

The General Illumination Model of shading was developed by explaining the various factors and mitigating coefficients to be applied to computing the intensity of each pixel. Factors include ambient light which is simulated by making objects glow, point light sources at infinity (parallel light rays), material properties, angle of incidence of light rays, attenuation coefficient, and the diffuse color coefficient. These values (except ambient) should be calculated for each light source. Special effects such as specular reflection also need to be taken into account.

Polygon shading uses interpolation and can be classified as Gouraud shading (interpolate between vertex intensities) and Phong shading (interpolate surface normals). All shading relies on the mock banding of the eye-brain vision process to produce the desired effect.

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