Schlick's approximation

In 3D computer graphics, Schlick's approximation is a formula for approximating the contributions of Fresnel terms in the specular reflection of light from non-conducting surfaces.

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 half the angle between the incoming and outgoing light directions. If the light is reflected due to the law of reflection, this means that $\theta$ is the angle between the light direction and the normal. $R_{0}$ is the reflectance at normal incidence (i.e., the value of the Fresnel term when $\theta =0$ or minimal reflection) and $n_{1},n_{2}$ are the indices of refraction at the interface. In computer graphics, one of the interfaces is usually air, meaning $n_{1}=1$.

See also

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