Autodesk LIGHTSCAPE, Manual

Page: 199 / 362

Testing for Artifacts
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The best solution in this situation would be either to
force a mesh element to occur under the table leg by
being explicit during the modeling stage (as
explained with the shadow leak artifact) or to ray
trace the light in a post-processing step, as shown in
the following example.
Mach Bands
The mach bands artifact usually appears as a bright
line along the edge of two adjacent mesh elements. It
usually occurs in areas where the mesh is too sparse
and can be eliminated by increasing the density of
the mesh.
Streaky Shadows
If a surface is made up of many oddly proportioned
surfaces such as long skinny triangles, the mesh
generated by the initiation process may also be made
up of many oddly proportioned elements. This
tends to increase the jagged shadow boundary and
shadow leak problems (described earlier) by making
the shadow edges appear streaky.
You can use ray tracing to produce better shadows. If
you want a good radiosity solution for interactive
manipulation, you can create the original surfaces
from more regularly shaped components during the
modeling stage.
Note: You can also do this during the Preparation
stage in Lightscape using the Create Surface
option on the Tools menu. For more information,
see “Creating Surfaces” on page 100.
Optimal shapes are regular, such as squares or equi-
lateral triangles. The following illustrations show
two examples of surfaces defined from two different
configurations of triangles and rectangles. The
surfaces on the right would produce better radiosity
results than the surfaces on the left.
Testing for Artifacts
Typically, you run two radiosity solutions to locate
and deal with visual artifacts.
The first solution usually does not have to go beyond
the number of iterations required to process the
contribution from the direct light sources, since
almost all artifacts are the result of the direct lights.
As a starting point, you can use the wizard to set the
meshing parameters.
Ray tracing image produces shadow of table leg
Images on left: Sub-optimal
configuration for radiosity
processing Images on right: Improved
configuration for radiosity
processing