Graphics Reference
In-Depth Information
reflectance
is defined for any surface as
·
ω
)
ω
.
F
dr
=
F
r
(
η
,
n
d
(1.17)
Ω
The value is known to be well approximated for real surfaces by a rational poly-
nomial (truncated Laurent series). For example, the expression
1
.
440
η
0
.
710
η
F
dr
=
−
+
+
0
.
668
+
0
.
0636
η
.
(1.18)
2
for diffuse Fresnel reflectance is utilized in the subsurface scattering models dis-
cussed in Chapter 4.
1.3 Structure of Rendering
Rendering
is the process of generating an image of an environment or scene from
a model. As noted previously, the model consists of the geometric shapes of
the objects in the environment together with reflection characteristics (BRDFs)
and other properties, such as the emission of the light sources. The problem of
constructing and representing geometric models, which is aptly known as
geomet-
ric modeling
, is a major subfield of computer graphics and is an active research
field in itself. Rendering and modeling are usually considered separate prob-
lems, although there is some overlap. As this topic is about rendering, geometric
modeling and the related field of animation are not really considered—rendering
algorithms that depend on geometry assume the geometric model has been con-
structed. It is important to remember though, that generating and animating re-
alistic models for CG characters is a
very
difficult task that involves both human
artistry and extensive technology resulting from many years of research.
1.3.1 Notion of Rendering
The conceptual process of rendering a scene (which can be a single object) amounts
to projecting the scene from a chosen viewpoint onto an imaginary
image plane
.
The
image
is a cropped rectangular section of the image plane that is divided into
a fine rectangular grid. Ultimately each grid cell corresponds to a
pixel
(picture
element) in the
rasterized
image. Each pixel normally stores three color compo-
nents, and it may store other values as well, such as depth, opacity, or percentage
coverage. The color values of a pixel come from the color of the object or objects
that project into the pixel. The process of determining the color of a scene object
at a point is known as
shading
.
