This shader effect is for adding a bright glowing around the very bright objects in the fractal. This effect is located on the Advanced Tab of The Render Panel.
The parameters are:
- Threshold: Defines the level of illumination used for the glow calculation. if it is set to a high value (1.0, for example), only the pure white objects are included on the glow calculation, by the contrary, if it is set to 0, every element of the image is used for the glow calculation.
- Passes:Number of passes used for the glow calculation, larger values produces a more unfocused glow, smaller ones will focus the glow around the bright objects.
For more information, consult the Wikipedia article about Bloom shader.
Here the glow is used to produce the heat effect, a bigger version of this image can be seen at Rfractals.Net