/* boundary4.c */
#include<stdio.h>
#include<stdlib.h>
#include"mypgm.h"

#define WHITE 255
#define BLACK 0
#define GRAY 128

void erode8( )
     /* 8-neighbor erosion of binary image           */
     /* input image1[y][x] ===> output image2[y][x]   */
{
  int counter;     /* number of neighboring figure points */
  int p_x, p_y;    /* coordinates of neighboring points */
  int x, y, m, n;  /* loop variable */
  
  x_size2 = x_size1;
  y_size2 = y_size1;
  for (y = 0; y < y_size2; y++)
    for (x = 0; x < x_size2; x++)
      image2[y][x] = image1[y][x];
  
  for (y = 0; y < y_size1; y++) {
    for (x = 0; x < x_size1; x++) {
      if (image1[y][x] == BLACK) {
	counter = 0;
	for (m = -1; m < 2; m++) {
	  for (n = -1; n < 2; n++) {
	    p_x = x + n;
	    p_y = y + m;
	    if (p_x >= 0 && p_x < x_size1 &&
		p_y >= 0 && p_y < y_size1 &&
		image1[p_y][p_x] == WHITE)
	      counter++;
	  }
	}
	if (counter > 0)
	  image2[y][x] = WHITE;
      }
    }
  }
}


void boundary4( )
     /* 4-connectivity boundary extraction of binary image */
     /* input image1[y][x] ===> output image2[y][x] */
{
  int x, y;  /* Loop variable */
  
  x_size2 = x_size1;
  y_size2 = y_size1;

  printf("Let's start 4-connectivity boundary extraction.\n");
  printf("\n");

  erode8();  /* 8-neighbor erosion */

  /* boundary extraction by subtracting image2 from image1 */
  
  for (y = 0; y < y_size2; y++)
    for (x = 0; x < x_size2; x++)
      if(image1[y][x] == BLACK)
	if (image2[y][x] == WHITE) image2[y][x] = BLACK;
	else image2[y][x] = GRAY;
}


main( )
{
  load_image_data( );  /* Input image1 */
  boundary4( );        /* 4-connectivity boundary extraction */
  save_image_data( );  /* Output image2 */
  return 0;
}