Schlick's approximation

In 3D computer graphics, Schlick's approximation is a formula for approximating the contribution of the Fresnel term 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:

$R(\theta )=R_{0}+(1-R_{0})(1-\cos \theta )^{5}$

$R_{0}=\left({\frac {n_{1}-n_{2}}{n_{1}+n_{2}}}\right)^{2}$

where $\theta$ 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 $\cos \theta =(H\cdot V)$. And $n_{1},\,n_{2}$ are the indices of refraction of the two medias at the interface and $R_{0}$ is the reflection coefficient for light incoming parallel to the normal (i.e., the value of the Fresnel term when $\theta =0$ or minimal reflection). In computer graphics, one of the interfaces is usually air, meaning that $n_{1}$ very well can be approximated as 1.

See also

• Phong reflection model
• Blinn-Phong shading model
• Fresnel equations