This module performs a double (x and y axes) symmetrization of an image.
It allows to avoid boundary effects 
when computing the Fourier Transform\index{Fourier Transform}
of an image, since such
a symmetrization followed by a Fourier Transform is equivalent to 
a Cosine Transform\index{Cosine Transform} of the original image.
The \verb+-i+ option performs the inverse operation (extraction of
the upleft corner). 

