#include<stdio.h>
#include<cv.h>

/* useful function for reading in ppm/pgm headers */
void getline(char *buf,FILE *fp)
  {  //read until end of line from fp
	  char *p=buf;
	  char c;
	  while ((c=fgetc(fp))!='\n')
	    {	   *p=c;
		    p++;
	    }
	  *p='\0';//terminate as string
  }



/* some useful variables */
     CvSize imagesize;
     int sizeX,sizeY;
     IplImage *ip,*ipout; 
     unsigned char *rawptr;
    char tstring[1000],inchar;
    FILE *fp;
    int maxval;
     char fname[100];




 int main(int argc,char **argv)
{
	int i;
	/* read in image */
     printf("name of input?\n");
     scanf("%s",fname);
    fp = fopen(fname, "rb");
    if (!fp)
    {
	fprintf(stderr, "Unable to open file `%s'\n", fname);
	exit(1);
    }
    getline(tstring,fp);
    fprintf(stderr,"scanned %s\n",tstring);
    if (! ((tstring[0]=='P') && (tstring[1]=='5')) )
        { 
         fprintf(stderr,"can only work with P5 versions of ppm images\n");
         exit(-1);
          }
         /*Check for comment and swallow whole line */
    getline(tstring,fp);
    while (tstring[0]=='#') getline(tstring,fp); //skip comments
    if (sscanf(tstring, "%d %d", &sizeX, &sizeY) != 2)
    {
	fprintf(stderr, "Error loading image `%s'\n", fname);
	exit(1);
    }
    getline(tstring,fp);
    while (tstring[0]=='#') getline(tstring,fp); //skip comments
     // throw away the maxval

    imagesize.width=sizeX; imagesize.height=sizeY;
     ip= cvCreateImage(imagesize,IPL_DEPTH_8U,1);// 3 channels RGB
                                                  //default is 4 bytes align
   ip->roi=0; // no region of interest  
     /* read image in one line at a time */
     rawptr= (unsigned char *) ip->imageData;
     for (i=0;i<sizeY;i++)
       {
       fread(rawptr,sizeX,1,fp);
       rawptr+= ip->widthStep; //increment padded line
       }
    fclose(fp);

    /* process image */
     ipout= cvCreateImage(imagesize,IPL_DEPTH_8U,1);
     cvCanny(ip,ipout,0.1,1.0,5); 
    /* output image */
     printf("name of output?\n");
     scanf("%s",fname);
    fp = fopen(fname, "wb");
    fprintf(fp,"P5\n%d %d\n255\n",ipout->width,ipout->height);
     /* write image in out line at a time */
     rawptr= (unsigned char *) ipout->imageData;
     for (i=0;i<sizeY;i++)
       {
       fwrite(rawptr,sizeX,1,fp);
       rawptr+= ipout->widthStep; //increment padded line
       }
    fclose(fp);

    }