separate out non-max suppression overlap code

kittydar.js

@@ -1,5 +1,6 @@
 var brain = require("brain"),
-    hog = require("hog-descriptor");
+    hog = require("hog-descriptor"),
+    nms = require("./nms");
 
 var network = require("./network.js");
 
@@ -59,7 +60,7 @@ var kittydar = {
       var kitties = kittydar.detectAtScale(resize.imagedata, resize.scale);
       cats = cats.concat(kitties);
     });
-    cats = this.combineOverlaps(cats);
+    cats = nms.combineOverlaps(cats, params.overlapThresh, params.minOverlaps);
 
     return cats;
   },
@@ -140,36 +141,6 @@ var kittydar = {
       }
     }
     return cats;
-  },
-
-  combineOverlaps: function(rects, overlap, min) {
-    // non-maximum suppression - remove overlapping rects
-    overlap = overlap || this.overlapThresh;
-    min = min || this.minOverlaps;
-
-    for (var i = 0; i < rects.length; i++) {
-      var r1 = rects[i];
-      r1.tally = 0; // number of rects it's suppressed
-
-      for (var j = 0; j < i; j++) {
-            r2 = rects[j];
-
-        if (doesOverlap(r1, r2)) {
-          if (r1.prob > r2.prob) {
-            r2.suppressed = true;
-            r1.tally += 1 + r2.tally;
-          }
-          else {
-            r1.suppressed = true;
-            r2.tally += 1 + r1.tally;
-          }
-        }
-      }
-    }
-    // only take a rect if it wasn't suppressed by any other rect
-    return rects.filter(function(rect) {
-      return !rect.suppressed && rect.tally >= min;
-    })
   }
 }
 
@@ -194,34 +165,18 @@ function resizeCanvas(canvas, width, height) {
   return resizeCanvas;
 }
 
-function doesOverlap(r1, r2, overlap) {
-  overlap = overlap || 0.5;
-
-  var overlapW, overlapH;
-  if (r1.x > r2.x) {
-    overlapW = Math.min((r2.x + r2.width) - r1.x, r1.width);
-  }
-  else {
-    overlapW = Math.min((r1.x + r1.width) - r2.x, r2.width);
-  }
-
-  if (r1.y > r2.y) {
-    overlapH = Math.min((r2.y + r2.height) - r1.y, r1.height);
+function createCanvas (width, height) {
+  if (typeof Canvas !== 'undefined') {
+    // have node-canvas
+    return new Canvas(width, height);
   }
   else {
-    overlapH = Math.min((r1.y + r1.height) - r2.y, r2.height);
-  }
-
-  if (overlapW <= 0 || overlapH <= 0) {
-    return false;
-  }
-  var intersect = overlapW * overlapH;
-  var union = (r1.width * r1.height) + (r2.width * r2.height) - (intersect * 2);
-
-  if (intersect / union > overlap) {
-    return true;
+    // in browser
+    var canvas = document.createElement('canvas');
+    canvas.setAttribute('width', width);
+    canvas.setAttribute('height', height);
+    return canvas;
   }
-  return false;
 }
 
 

nms.js

@@ -0,0 +1,73 @@
+/* non-maximum suppression - combine overlapping rects into the strongest one */
+
+exports.combineOverlaps = combineOverlaps;
+
+/* rects is an array of objects that look like:
+ *  {
+ *    x: // top left x coordinate,
+ *    y: // lop left y coordinate,
+ *    width: // width of rect,
+ *    height: // height of rect,
+ *    prob: // the higher, the more likely it will suppress other rects
+ *  }
+ * 
+ * minRatio is the min ratio of intersection area to union area of two rects
+ * to qualify them as overlapping.
+ *
+ * minOverlaps is the number of suppressions required for a rect
+ * to be included in the final returned set.
+ */
+function combineOverlaps(rects, minRatio, minOverlaps) {
+  console.log(minRatio, minOverlaps);
+  minRatio = minRatio || 0.5;
+  minOverlaps = minOverlaps || 1;
+
+  for (var i = 0; i < rects.length; i++) {
+    var r1 = rects[i];
+    r1.tally = 0; // number of rects it's suppressed
+
+    for (var j = 0; j < i; j++) {
+      var r2 = rects[j];
+
+      if (doesOverlap(r1, r2, minRatio)) {
+        if (r1.prob > r2.prob) {
+          r2.suppressed = true;
+          r1.tally += 1 + r2.tally;
+        }
+        else {
+          r1.suppressed = true;
+          r2.tally += 1 + r1.tally;
+        }
+      }
+    }
+  }
+  // only take a rect if it wasn't suppressed by any other rect
+  return rects.filter(function(rect) {
+    return !rect.suppressed && rect.tally >= minOverlaps;
+  })
+}
+
+function doesOverlap(r1, r2, minRatio) {
+  var overlapW, overlapH;
+  if (r1.x > r2.x) {
+    overlapW = Math.min((r2.x + r2.width) - r1.x, r1.width);
+  }
+  else {
+    overlapW = Math.min((r1.x + r1.width) - r2.x, r2.width);
+  }
+
+  if (r1.y > r2.y) {
+    overlapH = Math.min((r2.y + r2.height) - r1.y, r1.height);
+  }
+  else {
+    overlapH = Math.min((r1.y + r1.height) - r2.y, r2.height);
+  }
+
+  if (overlapW <= 0 || overlapH <= 0) {
+    return false;
+  }
+  var intersect = overlapW * overlapH;
+  var union = (r1.width * r1.height) + (r2.width * r2.height) - (intersect * 2);
+
+  return intersect / union > minRatio;
+}