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surface's diffuse reflection color . Adding the contributions from n light
sources and considering the ambient intensity , we can express the diffuse
component of our lighting formula as
n
NL
{
}
=+
  
max
, 0
,
(7.6)
diffuse
i
i
i
=
1
where the unit vector
L points from Q toward the i -th light source.
7.4 Specular Reflection
In addition to the uniform diffuse reflection, surfaces tend to reflect light strongly
along the path given by the reflection of the incident direction across the surface
normal. This results in the appearance of a shiny highlight on a surface called a
specularity . Unlike the diffuse reflection, the specular reflection visible on a sur-
face depends on the position of the viewer.
Figure 7.3 shows the normal vector N at a point Q on a surface, the unit di-
rection to viewer vector V , the unit direction to light vector L , and the direct re-
flection vector R calculated using Equation (6.90). Specular highlights are the
most intense when the reflection direction R points toward the viewer and de-
N
R
L
V
α
α
Q
Figure 7.3. The intensity of the specular reflection is related to the angle between the
direction to viewer vector V and the direct reflection vector R corresponding to the direc-
tion to light vector L .
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