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66 Chapter 2 ■ Edge-Detection Techniques

x += gau[k]*im->data[i][I1] + gau[k]*im->data[i][I2];
}
smx[i][j] = x; smy[i][j] = y;
}
}
void dxy_seperable_convolution (float** im, int nr, int nc, float *gau,
int width, float **sm, int which)
{
int i,j,k, I1, I2;
float x;
for (i=0; i<nr; i++)
for (j=0; j<nc; j++)
{
x = 0.0;
for (k=1; k<width; k++)
{
if (which == 0)
{
I1 = (i+k)%nr; I2 = (i-k+nr)%nr;
x += -gau[k]*im[I1][j] + gau[k]*im[I2][j];
}
else
{
I1 = (j+k)%nc; I2 = (j-k+nc)%nc;
x += -gau[k]*im[i][I1] + gau[k]*im[i][I2];
}
}
sm[i][j] = x;
}
}

void nonmax_suppress (float **dx, float **dy, int nr, int nc,
IMAGE mag, IMAGE ori)
{
int i,j;
float xx, yy, g2, g1, g3, g4, g, xc, yc;

for (i=1; i<mag->info->nr-1; i++)
{
for (j=1; j<mag->info->nc-1; j++)
{
mag->data[i][j] = 0;
/* Treat the x and y derivatives as components of a vector */
xc = dx[i][j];
yc = dy[i][j];
if (fabs(xc)<0.01 && fabs(yc)<0.01) continue;

g = norm (xc, yc);