Thread: histogram equilization alg.

HELP!!
Hello, I am writing a code for histogram equilization which will take a gray scale pgm image, read it equilize the picture then write it out. Now I am having a lot of errors specially in the read and write file, and an error in: in the type conversion of Npixels=(wXh)/256 and sum_hist = ((sum*Npixels) + .5; also in the use of buffer to output the image. can someone please help.

Code:

#include <iostream.h>
#include <math.h>
// read pgm grey scale image into memory cor[i][j]
void read_pgm(char * file_name)
{
  	int	 w, h;
   	char  	 buf[80];
	FILE	 * fp;

	// open file for reading 
	if((fp = fopen(file_name, "r")) == NULL) {
		fprintf(stderr, "readImage: Can't open %s\n", file_name);
		exit(1);
	}
   	// Verify that the image is in PGM format. 
   	fgets(buf, 70, fp);
   	if(strncmp(buf,"P5",2) != 0){
      		fprintf(stderr, "The file %s is not in PGM format", file_name);
      		fclose(fp);
      		exit(1);
   	}
	// skip all comment lines 
   	do { fgets(buf, 70, fp); } while(buf[0] == '#');     
	sscanf(buf, "%d %d", &w, &h);
   	do { fgets(buf, 70, fp); } while(buf[0] == '#');

        // read intensity values into memory 
	assign_mem(w, h); // assign a 2-D array cor for the image
	for (int i = 0; i < w; i++)
	  for (int j = 0; j < h; j++)
	    cor[i][j] = getc(fp);
	if (feof(fp) != 0) {
	  printf("something is wrong with this picture.\n");
	  exit(1);
	}
	fclose(fp);
}

// writes pgm grey scale image into memory cor[i][j]
void write_pgm(char * file_name)
{
	FILE	*out;

	if ((out = fopen(file_name, "wb")) == NULL) {
	  cout << "write_pgm: cannot open the file " 
  	       << file_name 
	       << " for writing" << endl;
          exit(1);
        }
			
	fprintf(out,"P5\n");
	fprintf(out,"%d %d\n", w, h);
	fprintf(out,"255\n");
	for (int i = 0; i < h; i++)
	  for (int j = 0; j < w; j++)
	    putc(int(cor[i][j]+0.5), out);
            // cor saves the image information

	fclose(out);
        return;
}

int main(){

	long i;
	long w[256];
	long h[256];
	long sum;
	long hist[256];
	long sum_hist[256];
	long Npixels = (w*h) / 256;	//error

	//read image
	 read_pgm("picture.pgm");	

	//clear histogram to 0
	 for (i=0; i < Npixels; i++)
		hist [i] = 0;
		 
	//calculate the histogram sum
	 sum = 0;
	 for (i=0; i<Npixels; i++)
	    hist[buffer[i]]++;		//error here 
	
	for (i = 0; i< 256; i++){
		sum += hist[i];
//error here in conversion "="
		sum_hist [i]= (sum * Npixels) + 0.5;
	}

	//transfor image using new sum 
	for (i = 0; i< Npixels; i++){
		buffer[i] = sum_hist(buffer[i]);  //error
	}


	//write image
	 write_pgm("picture.pgm");

return 0;
}