Like the {\sf fft2d} module, this one computes the Fast Fourier Transform 
\index{Fourier Transform} $v$
of a complex image $u$, specified by two Fimages (real and imaginary parts). 
However, it returns the result $v$ in polar coordinates, 
using two Fimages (the modulus $\rho$ and the phase $\varphi \in [-\pi,\pi]$)
such that $v=\rho e^{i\varphi}$.

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Several special cases can occur when you use this module as a 
C subroutine~:
\begin{itemize}
\item If $in\_im=NULL$, the input imaginary part is assumed to be zero 
everywhere.
\item If $out\_rho=NULL$ or $out\_theta=NULL$, the module assumes that you
don't need the corresponding output.
\end{itemize}
