Multiple Anchors have same IOU

Fixed the Todo for matching multiple anchors with the same IOU, and setting their value to 1. The previous version only picked the first anchor that had a maximum IOU. Now, if multiple anchors had the same IOU < 0.7, all of them will be set to a foreground class.

mrcnn/model.py

@@ -1495,8 +1495,8 @@ def build_rpn_targets(image_shape, anchors, gt_class_ids, gt_boxes, config):
     anchor_iou_max = overlaps[np.arange(overlaps.shape[0]), anchor_iou_argmax]
     rpn_match[(anchor_iou_max < 0.3) & (no_crowd_bool)] = -1
     # 2. Set an anchor for each GT box (regardless of IoU value).
-    # TODO: If multiple anchors have the same IoU match all of them
-    gt_iou_argmax = np.argmax(overlaps, axis=0)
+    # If multiple anchors have the same IoU match all of them
+    gt_iou_argmax = np.argwhere(overlaps == np.max(overlaps, axis=0))[:,0]
     rpn_match[gt_iou_argmax] = 1
     # 3. Set anchors with high overlap as positive.
     rpn_match[anchor_iou_max >= 0.7] = 1