FILTPHASE

The method *goldstein* is described in [9].
Basically the fringes become sharper after filtering because the peak
in the spectrum (caused by the fringes) is given a higher relative
weight. Method *spatialconv* simply is a spatial convolution with
a certain kernel function, e.g., a 3 point moving average. Method
*spectral* is a multiplication of the spectrum with the kernel
specified in an **input file** (e.g. a spectral low pass filter (LPF)).

Leijen 2009-04-14