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72 Chapter 2 ■ Edge-Detection Techniques

/* now apply the filter in the horizontal direction (to the columns) and */
/* apply this filter to the results of the previous one */
apply_ISEF_horizontal (y, y, A, B, nrows, ncols);
/* free up the memory */
free (B[0]); free(B);
free (A[0]); free(A);
}

void apply_ISEF_vertical (float **x, float **y, float **A, float **B,
int nrows, int ncols)
{
register int row, col;
float b1, b2;

b1 = (1.0 - b)/(1.0 + b);
b2 = b*b1;

/* compute boundary conditions */
for (col=0; col<ncols; col++)
{

/* boundary exists for 1st and last column */
A[0][col] = b1 * x[0][col];
B[nrows-1][col] = b2 * x[nrows-1][col];
}
/* compute causal component */
for (row=1; row<nrows; row++)
for (col=0; col<ncols; col++)
A[row][col] = b1 * x[row][col] + b * A[row-1][col];

/* compute anti-causal component */
for (row=nrows-2; row>=0; row--)
for (col=0; col<ncols; col++)
B[row][col] = b2 * x[row][col] + b * B[row+1][col];

/* boundary case for computing output of first filter */
for (col=0; col<ncols-1; col++)
y[nrows-1][col] = A[nrows-1][col];

/* now compute the output of the first filter and store in y */
/* this is the sum of the causal and anti-causal components */
for (row=0; row<nrows-2; row++)
for (col=0; col<ncols-1; col++)
y[row][col] = A[row][col] + B[row+1][col];
}
void apply_ISEF_horizontal (float **x, float **y, float **A, float **B,
int nrows, int ncols)