public void nonMax() {
nonMax = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g = nonMax.createGraphics();
g.setColor(new Color(0, 0, 0, 0));
g.fillRect(0, 0, width, height);
g.dispose();
magnitude = new int[height * width];
for (int y = 1; y < height - 1; y++) {
for (int x = 1; x < width - 1; x++) {
double xGrad = sX[y][x];
double yGrad = sY[y][x];
double gradMag = Math.hypot(xGrad, yGrad);
// perform non-maximal supression
double nMag = Math.hypot(sX[y - 1][x], sY[y - 1][x]);
double sMag = Math.hypot(sX[y + 1][x], sY[y + 1][x]);
double wMag = Math.hypot(sX[y][x - 1], sY[y][x - 1]);
double eMag = Math.hypot(sX[y][x + 1], sY[y][x + 1]);
double neMag = Math.hypot(sX[y - 1][x + 1], sY[y - 1][x + 1]);
double seMag = Math.hypot(sX[y + 1][x + 1], sY[y + 1][x + 1]);
double swMag = Math.hypot(sX[y + 1][x - 1], sY[y + 1][x - 1]);
double nwMag = Math.hypot(sX[y - 1][x - 1], sY[y - 1][x - 1]);
double tmp;
/*
* An explanation of what's happening here, for those who want
* to understand the source: This performs the "non-maximal
* supression" phase of the Canny edge detection in which we
* need to compare the gradient magnitude to that in the
* direction of the gradient; only if the value is a local
* maximum do we consider the point as an edge candidate.
*
* We need to break the comparison into a number of different
* cases depending on the gradient direction so that the
* appropriate values can be used. To avoid computing the
* gradient direction, we use two simple comparisons: first we
* check that the partial derivatives have the same sign (1)
* and then we check which is larger (2). As a consequence, we
* have reduced the problem to one of four identical cases that
* each test the central gradient magnitude against the values at
* two points with 'identical support'; what this means is that
* the geometry required to accurately interpolate the magnitude
* of gradient function at those points has an identical
* geometry (upto right-angled-rotation/reflection).
*
* When comparing the central gradient to the two interpolated
* values, we avoid performing any divisions by multiplying both
* sides of each inequality by the greater of the two partial
* derivatives. The common comparand is stored in a temporary
* variable (3) and reused in the mirror case (4).
*
*/
if (xGrad * yGrad <= (float) 0 /*(1)*/
? Math.abs(xGrad) >= Math.abs(yGrad) /*(2)*/
? (tmp = Math.abs(xGrad * gradMag))
>= Math.abs(yGrad * neMag - (xGrad + yGrad) * eMag) /*(3)*/
&& tmp > Math.abs(yGrad * swMag - (xGrad + yGrad) * wMag) /*(4)*/
: (tmp = Math.abs(yGrad * gradMag))
>= Math.abs(xGrad * neMag - (yGrad + xGrad) * nMag) /*(3)*/
&& tmp > Math.abs(xGrad * swMag - (yGrad + xGrad) * sMag) /*(4)*/
: Math.abs(xGrad) >= Math.abs(yGrad) /*(2)*/
? (tmp = Math.abs(xGrad * gradMag))
>= Math.abs(yGrad * seMag + (xGrad - yGrad) * eMag) /*(3)*/
&& tmp > Math.abs(yGrad * nwMag + (xGrad - yGrad) * wMag) /*(4)*/
: (tmp = Math.abs(yGrad * gradMag))
>= Math.abs(xGrad * seMag + (yGrad - xGrad) * sMag) /*(3)*/
&& tmp > Math.abs(xGrad * nwMag + (yGrad - xGrad) * nMag) /*(4)*/) {
magnitude[y * width + x] =
gradMag >= MAGNITUDE_LIMIT ? MAGNITUDE_MAX : (int) (MAGNITUDE_SCALE * gradMag);
// NOTE: The orientation of the edge is not employed by this
// implementation. It is a simple matter to compute it at
// this point as: Math.atan2(yGrad, xGrad);
} else {
magnitude[y * width + x] = 0;
}
}
}
ImageIcon icon2 = new ImageIcon(nonMax);
lbl2.setIcon(icon2);
}
