Caustic Tag

The caustic tag extends the camera object with the possibility to render your scene with caustics. But first of all what are caustics? Caustics are these nice light patterns you can see when the light shines through a glass of wine or through a lens. Caustics can be also seen when light is reflected at some reflective metal or plastic object.

The caustic tag works closely together with the "caustic photons" property of Light object. In the light object you can specify how many photons your light source emits. The photons are traced through the scene and are stored at the surfaces which they hit. The collections of all the photons in the scene are called the photon map.

After the photon tracing path the renderer collects the photons in the nearby area of any pixel and calculates the light intensity at that point.

To render caustics it is important that as many photons as possible hit the reflective or transparent surfaces and get collected in the photon map. If to less photons hit these material you will get quite ugly caustics as you can see on the first image below. Increasing the number of shot photons will cure that problem.

spot light which traced 5000 photons
spot light which traced 200.000 photons

Tips:

  • Use spot lights when possible since point lights for example shot their photons in all directions. With the spot light you can focus the photons in a direction which is of importance.
  • The light source offers a property called "pure photon light". Use this property to create some fake light sources which don't create direct lightning but only shot photons into the photon map.

Attention: You can only add a caustic tag to a camera object.

Properties

  • Strength: The intensity of the caustics.
  • Samples: The max. number of photons which will be used to estimate the intensity of caustic. The higher the value for samples is the higher the quality of the caustics. A to low number of samples cause quite irregular caustics.
samples=50
samples=400
  • Blur: Defines the indirectly radius in screen space in which photons will be collected to estimate the intensity of the caustic. The higher that value the smoother the caustics.
samples=400
blur=20
samples=400
blur=30

© 2001-2010 Martin Wengenmayer. All rights reserved.