int im_freqflt(in, filtermask, out)
IMAGE *in, *filtermask, *out;
im_freqflt() performs filtering in the frequency domain of the input image
held by the image descriptor in with a mask held by the descriptor filtermask
and writes the result on the image descriptor out.
Image sizes should be power of two and less or equal to 512. All images
should be one channel square images. Image filtermask is a non-complex one
channel image created by im_create_fmask(). Input image can be any type. If
input is complex, in and filtermask are multiplied using the function
If input is not complex then it is transformed into the frequency domain and
then it is multiplied with the filtermask. In the latter case the result is
inverse fourier transformed and clipped to the input image format using the
The function returns 0 on success and -1 on error.