#include <gandalf/image_invert.h>
Image inversion in Gandalf use gan_image_invert_[qsi].
The simplest call is
Gan_Image *pImage, *pInvImage; /* declare image and inverted image */
/* ... create and fill pImage ... */
/* invert image the simple way */
pInvImage = gan_image_invert_s ( pImage );
or else invert using a pre-allocated result image:
/* ... create and fill pImage, allocate pInvImage ... */
/* invert image the simple way */
gan_image_invert_q ( pImage, pInvImage );
and finally the in-place version:
/* ... create and fill pImage ... */
/* invert image in-place */
gan_image_invert_i ( pImage );