Update IoU functions (#10123)

Remove box area function and support expandable bbox_iou() calls.

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/metrics.py

@@ -227,13 +227,13 @@ def bbox_iou(box1, box2, xywh=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-7
 
     # Get the coordinates of bounding boxes
     if xywh:  # transform from xywh to xyxy
-        (x1, y1, w1, h1), (x2, y2, w2, h2) = box1.chunk(4, 1), box2.chunk(4, 1)
+        (x1, y1, w1, h1), (x2, y2, w2, h2) = box1.chunk(4, -1), box2.chunk(4, -1)
         w1_, h1_, w2_, h2_ = w1 / 2, h1 / 2, w2 / 2, h2 / 2
         b1_x1, b1_x2, b1_y1, b1_y2 = x1 - w1_, x1 + w1_, y1 - h1_, y1 + h1_
         b2_x1, b2_x2, b2_y1, b2_y2 = x2 - w2_, x2 + w2_, y2 - h2_, y2 + h2_
     else:  # x1, y1, x2, y2 = box1
-        b1_x1, b1_y1, b1_x2, b1_y2 = box1.chunk(4, 1)
-        b2_x1, b2_y1, b2_x2, b2_y2 = box2.chunk(4, 1)
+        b1_x1, b1_y1, b1_x2, b1_y2 = box1.chunk(4, -1)
+        b2_x1, b2_y1, b2_x2, b2_y2 = box2.chunk(4, -1)
         w1, h1 = b1_x2 - b1_x1, b1_y2 - b1_y1 + eps
         w2, h2 = b2_x2 - b2_x1, b2_y2 - b2_y1 + eps
 
@@ -263,11 +263,6 @@ def bbox_iou(box1, box2, xywh=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-7
     return iou  # IoU
 
 
-def box_area(box):
-    # box = xyxy(4,n)
-    return (box[2] - box[0]) * (box[3] - box[1])
-
-
 def box_iou(box1, box2, eps=1e-7):
     # https://github.com/pytorch/vision/blob/master/torchvision/ops/boxes.py
     """
@@ -282,11 +277,11 @@ def box_iou(box1, box2, eps=1e-7):
     """
 
     # inter(N,M) = (rb(N,M,2) - lt(N,M,2)).clamp(0).prod(2)
-    (a1, a2), (b1, b2) = box1[:, None].chunk(2, 2), box2.chunk(2, 1)
+    (a1, a2), (b1, b2) = box1.unsqueeze(1).chunk(2, 2), box2.unsqueeze(0).chunk(2, 2)
     inter = (torch.min(a2, b2) - torch.max(a1, b1)).clamp(0).prod(2)
 
     # IoU = inter / (area1 + area2 - inter)
-    return inter / (box_area(box1.T)[:, None] + box_area(box2.T) - inter + eps)
+    return inter / ((a2 - a1).prod(2) + (b2 - b1).prod(2) - inter + eps)
 
 
 def bbox_ioa(box1, box2, eps=1e-7):