freegroup · June 5, 2020 22:46 · Nov 7, 2016 · Nov 7, 2016
diff --git a/otsu.js b/otsu.js
@@ -1,4 +1,4 @@
-// Read https://en.wikipedia.org/wiki/Otsu%27s_method
+// Read https://en.wikipedia.org/wiki/Otsu%27s_method (added this since JS examples in wikipedia didn't work)
 
 function otsu(histData /* Array of 256 greyscale values */, total /* Total number of pixels */) {
     let sum = 0;

diff --git a/otsu.js b/otsu.js
@@ -0,0 +1,37 @@
+// Read https://en.wikipedia.org/wiki/Otsu%27s_method
+
+function otsu(histData /* Array of 256 greyscale values */, total /* Total number of pixels */) {
+    let sum = 0;
+    for (let t=0 ; t<256 ; t++) sum += t * histData[t];
+
+    let sumB = 0;
+    let wB = 0;
+    let wF = 0;
+
+    let varMax = 0;
+    let threshold = 0;
+
+    for (let t=0 ; t<256 ; t++) {
+        wB += histData[t];               // Weight Background
+        if (wB == 0) continue;
+
+        wF = total - wB;                 // Weight Foreground
+        if (wF == 0) break;
+
+        sumB += t * histData[t];
+
+        let mB = sumB / wB;            // Mean Background
+        let mF = (sum - sumB) / wF;    // Mean Foreground
+
+        // Calculate Between Class Variance
+        let varBetween = wB * wF * (mB - mF) * (mB - mF);
+
+        // Check if new maximum found
+        if (varBetween > varMax) {
+            varMax = varBetween;
+            threshold = t;
+        }
+    }
+
+    return threshold;
+}
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