Scene Creation

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.

Images from
Henrik Wann Jensen's
Animations Page

Caustics from a
rotating glass cube

The Light of
Mies van der Rohe