In 3D computer graphics, Schlick's approximation, named after Christophe Schlick, is a formula for approximating the contribution of the Fresnel factor in the specular reflection of light from a non-conducting interface (surface) between two media.
According to Schlick's model, the specular reflection coefficient R can be approximated by:
where is the angle between the viewing direction and the half-angle direction, which is halfway between the incident light direction and the viewing direction, hence . And are the indices of refraction of the two medias at the interface and is the reflection coefficient for light incoming parallel to the normal (i.e., the value of the Fresnel term when or minimal reflection). In computer graphics, one of the interfaces is usually air, meaning that very well can be approximated as 1.