Before anything else, let's look at some example programs.

@section Gradients
The image processing equivalent of "Hello world":
@example

#include <vcl_iostream.h>
#include <vil/vil_load.h>
#include <vil/vil_save.h>
#include <vepl/vepl_gradient_mag.h>

int main(int argc, char** argv)
@{
  // The input image:
  vil_image_view<unsigned char> in = vil_load(argv[1]);

  // The filter:
  vil_image_view<unsigned char> out = vepl_gradient_mag(in);

  // Write output:
  vil_save(out, argv[2]);
  vcl_cout << "Written the gradrient image to " << argv[2] << vcl_endl;

  return 0;
@}
@end example
This example takes one grey-level image, and creates a second whose pixel values are the
gradient magnitudes of the first.
