# blinn half vector

i still dont get it, everywhere i go i see H defined as (V+L)/2 , with V and L normalized vecs
but, shouldnt H be normalized as well?
if so, what’s the use of dividing it by 2?
thanks for your help

H is an approximation of an apporximation.

H’ ~ R = 2(N.L)N - L

Where
H’ = (L + V)/ | L + V |

H = (L +V)/2 ~ H’

Because
1/2 ~ | L + V |

When
|L| = |V| = 1

I think the equations are right. Double check in your favorite copy of Foley et al.

[This message has been edited by PK (edited 03-14-2003).]

You are perfectly right. H should be normalized. The equation is usually written that way, to state that H is the average of L and V, and after that you should normalize H. Of course, you can skip the division, since in that case it’s mathematically equivalent.

oh thanks it finally makes some sense
pk: i think the approximation only works in the viewable range of R since i just dont see how | L + V | could be ~ 2 even if |L|=|V|=1, and i wouldnt say that H (or H’) ~ R because H is usually far away from R and it’s being dotted with N, while R has to be dotted with V
anyway thanks again, this H thing was just driving me crazy