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62 Chapter 2 ■ Edge-Detection Techniques

2.9 Source Code for the Canny Edge Detector

/* Canny edge detection */
#include “stdio.h“
#include “cv.h“
#include “highgui.h“

/* Scale floating point magnitudes and angles to 8 bits */
#define ORI_SCALE 40.0
#define MAG_SCALE 20.0
#define PI 3.1415926535

/* Biggest possible filter mask */
#define MAX_MASK_SIZE 20

/* Fraction of pixels that should be above the HIGH threshold */
float ratio = 0.1f;
int WIDTH = 0;

int range (IMAGE x, int i, int j)
{
if ( (i>=0) && (i<x->info->nr) && (j>=0) && (j<x->info->nc) )
return 1;
else return 0;
}

float norm (float x, float y)
{
return (float) sqrt ( (double)(x*x + y*y) );
}

void canny (float s, IMAGE im, IMAGE mag, IMAGE ori)
{
int width;
float **smx,**smy;
float **dx,**dy;
int i,j,n;
float gau[MAX_MASK_SIZE], dgau[MAX_MASK_SIZE], z;

/* Create a Gaussian and a derivative of Gaussian filter mask */
for(i=0; i<MAX_MASK_SIZE; i++)
{
gau[i] = meanGauss ((float)i, s);
if (gau[i] < 0.005)
{
width = i;
break;
}