The Gaussian minus exponential distribution is a convolution of a normal distribution with (minus) an exponential distribution.

In mathematics, the Dirichlet convolution is a binary operation defined for arithmetic functions it is important in number theory.

This is the radius of the circular convolution. It is the most important parameter for using this plugin. For most images the default value of 1.0 should give good results. Select a higher value when your image is very blurred.