Caustics are an effect
of indirect light transmission in which light travelling from the
light source is reflected or transmitted by another object before
illuminating a surface. In the simulated scene light is reflected
from or refracted through the window glass and the caustics are
bright patterns of light which appear on the nearby surfaces.
Caustics produced in Softimage XSI describe an effect of
specular light transmission calculated at the rendering stage. A
method called distribution ray tracing which samples in all
directions can be used to calculate caustic effects however it takes
much longer to compute and render. Mental Ray the renderer in
Softimage XSI uses the more efficient technique of Photon Mapping to
produce the same effect.
A caustic is created in a rendered
scene when photons emitted from a light source pass through one or
more specular reflections and refractions and hit a surface to be
diffusely reflected to the camera. Caustics appear in the scene as a
bright pattern of light on a diffuse surface. In this scene the
highly specular glass surface casts caustics when iluminated by a
bright light.
Indirect Illumination in a scene is controlled
by Global Illumnation a subset of which is Caustics. At the
rendering stage caustics are activated seperately from full Global
Ilumination which allows better control of both effects. Caustics
can be activated without global illumination and in this case
calculated rendering time for caustic effects can be similar to that
of raytracing. The production of caustic effects are based on photon
map file information but are controlled by parameters during scene
creation and rendering.
The two images to the left are taken
from the site of Henrik Wann Jensen who was one of the people who
developed photon mapping. The rotating glass cube is an animation
which demonstrates animatable caustic effects. The Light of Mies Van
Der Rohe concerns lighting in architecture in which caustics can
play an important role in the simulation of real-life lighting.
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