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Clarisse 4.0 User Guide

Clamping is a simple biased method which allows to reduce fireflies due, for example, to under sampling and low probability paths ending near light sources. Indeed, inverse square distance law states that the intensity of a light  is inversely proportional to the square of the distance from the source. This means that path ending on surfaces near a light source can have extremely high energy value. This generally is resolved by brute force oversampling as low probability path contributions are balanced by the high number of high probability paths that return the expected energy value.

Note

Since Clarisse 4.0 SP5, the path tracer offers a novel method to reduce considerably fireflies in renders. For more information please refer to the Fireflies Filtering section.

 

Example of a low probability path providing high energy

Example of a low probability path providing high energy

 

The path tracer provides you with clamping controls allowing you to specify a maximum luminance threshold (10.0 by default) to clamp values beyond this threshold in order reduce fireflies and noise in your renders. However you may notice an energy loss in your renders because diffuse illumination and reflections/transmissions may appear dimmed out. However, this tradeoff is usually more acceptable than the noise.

Disabling Clamping

It is possible to disable clamping by setting Clamping Threshold to -1 or clearing its value and pressing Return in the Attribute Editor.

Clamping Mode

Using the Clamping Mode attribute, it is possible to set which the method the path tracer uses to perform clamping. When Clamping Mode is set to:

  • Integration Level, the path tracer performs clamping at the end of the sample path integration. This method tries to minimize the loss of energy and offers per channel clamping thresholds. However, since it is performed at path integration, is doesn't work with AOVs and LPEs which is very problematic if you need to reconstruct the beauty in comp. Because of this limitation, this method is now deprecated and will be removed in future versions of Clarisse.
  • Path Level, the path tracer performs clamping on each individual path. This method may loose slightly more energy than Integration Level however, it works with AOVs and LPEs. This is the new default and the recommended method to use.

 

Note

Clamping is only performed on indirect paths so that all sharp highlights and dynamic range of direct lighting are preserved even when setting an aggressive clamping threshold of 1.0.

 

Fireflies due to the reflection of sun

Fireflies due to the reflection of sun

With a very aggressive Indirect Diffuse clamping value set to 1.0 fireflies disappear

With a very aggressive Indirect Diffuse clamping value set to 1.0 fireflies disappear

Even with an aggressive clamping value of 1.0 we keep all the dynamic range.

Even with an aggressive clamping value of 1.0 we keep all the dynamic range.

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