Note: This is for a single light.  If multiple lights are used, one computes a colour for each light source (and sums all the colours up).

For computational efficiency, Blinn modified the Phong model.  Instead of basing the specular reflection on the angle α between r and v, it is based on the angle β between h and n.  Here, h is the halfway vector, which is halfway between s and v.



h is slightly faster to compute than r.  Note though, β is a different angle than α.  Using a different angle affects the specular reflection.  However, the shininess can be modified to provide a similar effect as Phong shading.



A light’s specular component ls is reflected by a surface.  The amount of light reflection at each vertex is based on the halfway vector h, the surface normal n,  and the surface specular material, ms.

The colour resulting from the specular reflection is

where n is the shininess.

High

Exercise
Fill out the following table for the terms in the Blinn-Phong reflectance model.

Hint:  remember the equation