  The Transport-of-Intensity equation (TIE) has been proven as a standard
approach for phase retrieval. Some high efficiency solving methods for the TIE,
extensively used in many works, are based on a Fourier-Transform (FT). However,
to solve the TIE by these methods several assumptions have to be made. A common
assumption is that there are no zero values for the intensity distribution
allowed. The two most widespread Fourier-based approaches have further
restrictions. One of these requires the uniformity of the intensity
distribution and the other assumes the collinearity of the intensity and phase
gradients. In this paper, we present an approach, which does not need any of
these assumptions and consequently extends the application domain of the TIE.
