/*********************************************************/
/*   program 23: erosion and dilation                    */
/*********************************************************/

#define  XSIZE  640
#define  YSIZE  480

main()
  {
  unsigned char *ip;
  unsigned char *op;
  unsigned char *i1,*i2,*i3;
  unsigned char *o1,*o2,*o3;
  long  int  x,y;

  /* erode mask: */
  unsigned char m[3][3] = {0,0,0,0,0,0,0,0,0};

  /* dilate mask:
  unsigned char m[3][3] = {255,255,255,255,255,255,255,255,255};
  */

  /* allocate input and output memory buffers */
  ip = (unsigned char *) malloc (XSIZE*YSIZE);
  op = (unsigned char *) malloc (XSIZE*YSIZE);

  /* read the input image (one plane image) */
  read_image("input",ip);

  /* initialize pointers into buffers */
  i2 = ip;
  i3 = ip + XSIZE;
  o2 = op;
  o3 = op + XSIZE;

  /* process all lines of image */
  for (y = 1; y < (YSIZE-1); y++)
    {
    /* set pointers for this line */
    i1 = i2;
    i2 = i3;
    i3 = i3 + XSIZE;
    o1 = o2;
    o2 = o3;
    o3 = o3 + XSIZE;

    /* process all pixels in line */
    for (x = 1; x < (XSIZE-1); x++)
      {
      /* check neighborhood */
      if ((*(i1+x-1)==m[0][0]) &&
          (*(i1+x+0)==m[0][1]) &&
          (*(i1+x+1)==m[0][2]) &&
          (*(i2+x-1)==m[1][0]) &&
          (*(i2+x+0)==m[1][1]) &&
          (*(i2+x+1)==m[1][2]) &&
          (*(i3+x-1)==m[2][0]) &&
          (*(i3+x+0)==m[2][1]) &&
          (*(i3+x+1)==m[2][2]))
        {
        *(o2+x) = m[1][1];
        }
      else
        {
        *(o2+x) = 255 - m[1][1];
        }
      }
    }

  /* write the output image */
  write_image("output",op);

  /* free memory buffers */
  free(ip);
  free(op);
}