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>Blender Documentation Volume I - User Guide: Last modified April 29 2004 S68</TH
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>Specular Reflection</H1
><P
>Unlike Diffusion, Specular reflection is <I
CLASS="emphasis"
>viewpoint
dependent</I
>. According to Snell's Law, light striking a specular 
surface will be reflected at
an angle which mirrors the incident light angle, which makes the viewing angle
very important. Specular reflection forms tight, bright highlights,
making the surface appear glossy (<A
HREF="x3986.html#BSG.MAT.F.S68.103"
>Figure 3</A
>).
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><P
><B
>Figure 3. Specular Reflection.</B
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><P
>In reality, Diffusion and Specular reflection are generated by exactly
the same process of light scattering. Diffusion is dominant from a surface which 
has so
much small-scale roughness in the surface, with respect to wavelength,  
that light is reflected in
many different directions from each tiny bit of the surface,
with tiny changes in surface
angle. 
</P
><P
>&#13;Specular reflection, on the other hand, dominates on a surface which is smooth, 
with respect to wavelength. This implies that the scattered rays from each point 
of the surface are directed almost in the same direction, rather than being 
diffusely scattered. It's just a
matter of the scale of the detail. If the surface
roughness is much smaller than the wavelength of the incident
light it appears flat and acts as a mirror. 
</P
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>&#13;It is important to stress that the Specular reflection phenomenon discussed here
is not the reflection we would see in a mirror, but rather the light highlights 
we would see
on a glossy surface. To obtain true mirror-like reflections you would need to 
use a raytracer. Blender is not
a raytracer as such, but
it can produce convincing mirror-like surfaces via careful application of
textures, as will be shown later on.
</P
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><P
>&#13;Like Diffusion, Specular reflection has a number of different implementations,
or <I
CLASS="emphasis"
>specular shaders</I
>. Again, each of these implementations 
shares two
common parameters: the <I
CLASS="emphasis"
>Specular colour</I
> and the
energy of the specularity, in the [0-2] range. This effectivelly allows
more energy to be shed as specular reflection as there is incident energy.
As a result, a material has at least two different colors, a diffuse,
and a specular one. The specular color is normally set to pure white, but it can
be set to different values to obtain interesting effects.
</P
><P
>The four specular shaders are:</P
><P
></P
><UL
><LI
><P
><I
CLASS="emphasis"
>CookTorr</I
> -- This was Blender's only 
Specular Shader
    up to version 2.27. Indeed, up to that version it was not possible to
    separately set diffuse and specular shaders and there was just one plain 
material
    implementation. Besides the two standard parameters this shader
    uses a third, <I
CLASS="emphasis"
>hardness</I
>, which regulates the width of 
the specular highlights. The lower the hardness, the wider the highlights.
    </P
></LI
><LI
><P
><I
CLASS="emphasis"
>Phong</I
> -- This is a different mathematical 
algorithm, used to compute specular highlights. It is not very different from 
CookTor, and it is governed by the same three parameters.
</P
></LI
><LI
><P
><I
CLASS="emphasis"
>Blinn</I
> -- This is a more 'physical' 
specular
    shader, thought to match the Oren-Nayar diffuse one. It is more physical
    because it
    adds a fourth parameter, an <I
CLASS="emphasis"
>index of refraction (IOR)</I
>, 
to the aforementioned three.
    This parameter is not actually used to compute refraction of rays (a ray-
tracer
    is needed for that), but to correctly compute specular reflection
    intensity and extension via Snell's Law. Hardness and Specular
    parameters give additional degrees of freedom.
</P
></LI
><LI
><P
><I
CLASS="emphasis"
>Toon</I
> -- This specular
    shader matches the Toon diffuse one. It is designed to produce
    the sharp, uniform highlights of toons. It has no hardness but
    rather a Size and Smooth pair of parameters which dictate the
    extension and sharpness of the specular highlights.
</P
></LI
></UL
><P
>Thanks to this flexible implementation, which keeps separate
the diffuse and specular reflection phenomena,
Blender allows us to easily control how much of the incident light
striking a point on a surface is diffusely scattered, how much is
reflected as specularity, and how much is absorbed. This, in turn, determines in 
what directions (and in what amounts) the
light is reflected from a given light source; that is, from what sources (and in 
what amounts) the light is reflected toward a given point on the viewing plane.
</P
><P
>&#13;It is very important to remember that the material color is just one
element in the rendering process. The color is actually the product of the light 
color and the
material color.
</P
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