int im_zone(image, size)
int im_fzone(image, size)
im_fzone() 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.
im_zone() behaves exactly as im_fzone(), but writes a FMTUCHAR image scaled to the range 0-255.
RETURN VALUEThe function returns 0 on success and -1 on error.
AUTHORN. Dessipris - 10/05/1991