void Otsu(ImagePlus imp, int radius, double par1, double par2, boolean doIwhite) {
// Otsu's threshold algorithm
// C++ code by Jordan Bevik <*****@*****.**>
// ported to ImageJ plugin by G.Landini. Same algorithm as in Auto_Threshold, this time on local
// circular regions
int[] data;
int w = imp.getWidth();
int h = imp.getHeight();
int position;
int radiusx2 = radius * 2;
ImageProcessor ip = imp.getProcessor();
byte[] pixels = (byte[]) ip.getPixels();
byte[] pixelsOut =
new byte
[pixels.length]; // need this to avoid changing the image data (and further histograms)
byte object;
byte backg;
if (doIwhite) {
object = (byte) 0xff;
backg = (byte) 0;
} else {
object = (byte) 0;
backg = (byte) 0xff;
}
int k, kStar; // k = the current threshold; kStar = optimal threshold
int N1, N; // N1 = # points with intensity <=k; N = total number of points
double BCV, BCVmax; // The current Between Class Variance and maximum BCV
double num, denom; // temporary bookeeping
int Sk; // The total intensity for all histogram points <=k
int S,
L =
256; // The total intensity of the image. Need to hange here if modifying for >8 bits
// images
int roiy;
Roi roi = new OvalRoi(0, 0, radiusx2, radiusx2);
// ip.setRoi(roi);
for (int y = 0; y < h; y++) {
IJ.showProgress(
(double) (y) / (h - 1)); // this method is slow, so let's show the progress bar
roiy = y - radius;
for (int x = 0; x < w; x++) {
roi.setLocation(x - radius, roiy);
ip.setRoi(roi);
// ip.setRoi(new OvalRoi(x-radius, roiy, radiusx2, radiusx2));
position = x + y * w;
data = ip.getHistogram();
// Initialize values:
S = N = 0;
for (k = 0; k < L; k++) {
S += k * data[k]; // Total histogram intensity
N += data[k]; // Total number of data points
}
Sk = 0;
N1 = data[0]; // The entry for zero intensity
BCV = 0;
BCVmax = 0;
kStar = 0;
// Look at each possible threshold value,
// calculate the between-class variance, and decide if it's a max
for (k = 1; k < L - 1; k++) { // No need to check endpoints k = 0 or k = L-1
Sk += k * data[k];
N1 += data[k];
// The float casting here is to avoid compiler warning about loss of precision and
// will prevent overflow in the case of large saturated images
denom = (double) (N1) * (N - N1); // Maximum value of denom is (N^2)/4 = approx. 3E10
if (denom != 0) {
// Float here is to avoid loss of precision when dividing
num = ((double) N1 / N) * S - Sk; // Maximum value of num = 255*N = approx 8E7
BCV = (num * num) / denom;
} else BCV = 0;
if (BCV >= BCVmax) { // Assign the best threshold found so far
BCVmax = BCV;
kStar = k;
}
}
// kStar += 1; // Use QTI convention that intensity -> 1 if intensity >= k
// (the algorithm was developed for I-> 1 if I <= k.)
// return kStar;
pixelsOut[position] = ((int) (pixels[position] & 0xff) > kStar) ? object : backg;
}
}
for (position = 0; position < w * h; position++)
pixels[position] = pixelsOut[position]; // update with thresholded pixels
}
