bbox_iou() stability and speed improvements (#2385)

utils/general.py

@@ -312,7 +312,7 @@ def clip_coords(boxes, img_shape):
     boxes[:, 3].clamp_(0, img_shape[0])  # y2
 
 
-def bbox_iou(box1, box2, x1y1x2y2=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-9):
+def bbox_iou(box1, box2, x1y1x2y2=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-7):
     # Returns the IoU of box1 to box2. box1 is 4, box2 is nx4
     box2 = box2.T
 
@@ -348,7 +348,7 @@ def bbox_iou(box1, box2, x1y1x2y2=True, GIoU=False, DIoU=False, CIoU=False, eps=
             elif CIoU:  # https://github.com/Zzh-tju/DIoU-SSD-pytorch/blob/master/utils/box/box_utils.py#L47
                 v = (4 / math.pi ** 2) * torch.pow(torch.atan(w2 / h2) - torch.atan(w1 / h1), 2)
                 with torch.no_grad():
-                    alpha = v / ((1 + eps) - iou + v)
+                    alpha = v / (v - iou + (1 + eps))
                 return iou - (rho2 / c2 + v * alpha)  # CIoU
         else:  # GIoU https://arxiv.org/pdf/1902.09630.pdf
             c_area = cw * ch + eps  # convex area