Blinn-Phong approximates a Gaussian distribution as the specular exponent increases [Lyon1993]. [Olano2010] has shown the following relation in terms of the angle
between and :
This makes the spherical Gaussian blur an excellent and appropriate choice for generating environmental maps. By extending the Gaussian blur's separable property, it is possible to implement it in
(where is a kernel radius) for reasonably small values.
Pre-filtered Mipmapped Radiance Environment …