[Insight-developers] RecursiveGaussianImageFilter

[Gunnar Farnebäck]

I wrote:
> These numbers look like they may be truncated approximations of some
> other values. If that is the case I have three questions:
> 
> 1. Why is this implementation using so few digits?
> 2. Has the truncation been made in a way which takes, e.g., the
>    resulting DC response into account?
> 3. Where do the numbers come from in the first place?

I think I can answer those questions myself now.

3. The numbers are coefficients in an approximation of the derivative
   of the Gaussian by a specific kind of series. See section 5 of the
   technical report:
   R. Deriche. Recursively implementing the gaussian and its
   derivatives. Technical Report 1893, INRIA, Unité de Recherche
   Sophia-Antipolis, 1993 

   This should probably be added to the code comments. Currently only
   the PAMI 1990 paper is referenced, but that doesn't include these
   implementation details, as far as I can tell.

1. Because those are the numbers given in the technical report.

2. Never mind, the non-zero DC response is probably not directly
   related to those numbers.

/Gunnar