im_grid - split a vertical image into a grid of smaller images
im_grid( IMAGE *in, IMAGE *out,
int tile_height, int across, int down )
im_grid(3) slices image in into a set of tiles, each the same width as
in and of height tile_height and rearranges the tiles into a grid with
across tiles across and down tiles down.
It is useful for loading volumetric images (for example, CT or PET
scans) where more than 2 dimensions need to be displayed.
The current implementation is optimised for the case where image in is
thin and tall and across and down are large.
The function returns 0 on success and -1 on error.
Imperial College 2005
4 August 2005