/*
 * usage:  thresh <lo> <hi> <inputfile>
 *
 * thresholds the input file ("-" for stdin), producing a binary
 * PGM image.  all pixels between lo and hi inclusive become white;
 * all others become black.
 */

#include <iostream>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>

#include <math.h>

using namespace std;

void write_pgm( FILE* f, int width, int height, unsigned char* data );
unsigned char* read_pgm( char* filename, int* width, int* height );

main( int argc, char **argv )
{
     int iwidth, iheight;
     unsigned char* image;
     int i;
     int lo, hi;
     

     if ( argc != 4 )
     {
	  fprintf( stderr, "usage: %s lo hi imagefile\n", argv[0] );
	  exit( 1 );
     }

     lo = atoi( argv[1] );
     hi = atoi( argv[2] );
     
     image = read_pgm( argv[3], &iwidth, &iheight );
     if ( image == NULL )
     {
	  fprintf( stderr, "error reading image file.\n" );
	  exit( 1 );
     }

     for ( i = 0; i < iwidth*iheight; ++i )
     {
	  if ( image[i] >= lo && image[i] <= hi )
	       image[i] = 255;
	  else
	       image[i] = 0;
     }
     
     write_pgm( stdout, iwidth, iheight, image );
}

unsigned char* read_pgm( char* filename, int* width, int* height )
{
     char buffer[80];
     int phase = 0;
     int type, maxval;
     int j;
     unsigned char* data;
     FILE* f;

     if ( strcmp( filename, "-" ) == 0 )
     {
	  f = stdin;
     }
     else
     {
	  f = fopen( filename, "rb" );
	  if ( f == NULL )
	       return NULL;
     }
     
     while ( phase < 4 )
     {
	  fgets( buffer, 80, f );
	  if ( buffer[0] == '#' ) continue;
	  switch( phase )
	  {
	     case 0: j = sscanf( buffer, "P%d %d %d %d\n", &type, width, height, &maxval ); break;
	     case 1: j = sscanf( buffer, "%d %d %d\n", width, height, &maxval ); break;
	     case 2: j = sscanf( buffer, "%d %d\n", height, &maxval ); break;
	     case 3: j = sscanf( buffer, "%d\n", &maxval ); break;
	     case 4: j = 0; break;
	  }
	  phase += j;
     }

     if ( type != 5 )
     {
	  fprintf( stderr, "bad input image format.\n" );
	  return NULL;
     }

     data = (unsigned char*)malloc ( *width * *height );
     fread( data, *width * *height, 1, f );

     fclose( f );
     
     return data;
}

void write_pgm( FILE* f, int width, int height, unsigned char* data )
{
     fprintf( f, "P5\n%d %d\n%d\n", width, height, 255 );
     fwrite( data, width*height, 1, f );
     fclose( f );
}