9

Modeling Global Illum ination with R adiosity 55
Radiosity: A ray of light that hits a surface is reflected by
multiple diffuse rays, which can themselves illuminate other
sur faces. Surfaces are subdiv ided to increase accuracy of the
solution.
Inearlyversionsoftheradiosityalgorithm,the
distribution of light among mesh elements had
to be completely calculated before any useful
results could be displayed on the screen. Even
though the result was view-i ndependent, the
preprocessing took a considerable amount of time.
In 1988, progressive refinement was invented. This
techniquedisplaysimmediatevisualresultsthat
canprogressivelyimproveinaccuracyandvisual
quality. In 1999, the technique called stochastic
relaxation r adiosity (SRR) was invented. The
SRRalgorithmformsthebasisofthecommercial
radiosity systems provided by Autodesk.
An Integrated S olution
Although the ray-tracing and radiosity algorithms
areverydifferent,theyareinmanyways
complementary. Each technique has advantages
and disadvantages.
Lighting
Algorithm
Advantages Disadva ntages
Ray-Tracing
Accurately renders
direct illumination,
shadows, specular
reflection s, and
transparency effects.
Memory Efficient
Computationally
expensive. The
time required to
produce an image is
greatly affected by
the num ber of light
sources.
Process must
be repeated for
each view (view
dependent).
Doesn’t account
for diffuse
interreflections.
Radiosity Calculates diffuse
interreflections
between sur faces.
Provides view
independent
solutions for fast
display of arbitrary
views.
Offers immediate
visual results.
3D mesh requires
more memory than
the original surfaces.
Surface sampling
algorithm is more
susceptible to
imaging ar tifacts
than ray-tracing.
Doesn’t account for
specular reflections
or transparency
effects.
Neither radiosity nor ray-tracing offers a
complete solution for simulating all global
illuminat ion effects. Radiosity excels at
rendering diffuse-to-diffuse inter-reflections, and
ray-tracing excels at rendering specular reflections.
By integrating both techniques with a production
quality scanline rendering system, 3ds Max offers
the best of both worlds. After you create a radiosity
solution, you can render a two-dimensional
view of it. In your 3ds Max scene, ray-tracing
adds effects in addition to those that radiosity
provides: lights can provide ra y-traced shadows,
and materials can provide ray-traced reflections
and refractions. The rendered scene combines
both techniques, and appears more realistic than
either technique alone could pro vide.
By integrating ray-tracing and radiosity, 3ds Max
offers a full range of visualization possibilities,