creates a float one band image of a zone plate of size size by size. Pels are
in the range [-1,+1]. The zone plate has spatial frequencies increasing from
0 the center (at size/2, size/2) up to infinity at the edges. size must be
positive and even.
behaves exactly as im_fzone(), but writes a FMTUCHAR image scaled to the range
The function returns 0 on success and -1 on error.