im_rotquad - rotates the four quadrants of an image
int im_rotquad(in, out)
IMAGE *in, *out;
im_rotquad rotates the four quadrants of the image held by the image
descriptor in and writes the result on the image descriptor out.
The function is used primarily to rotate a fourier transform in such a
way that the coordinate (0,0) is near the centre of the image, the so-
called optical transform.
The function operates on any input; output has the same format, sizes
and bands as input.
The function returns 0 on success and -1 on error.
im_fwfft(3), im_invfft(3), im_scaleps(3).
N. Dessipris - 06/07/1990
07 July 1990