the comparison of nms in speed
method 1: thresh=0.7, time wastes:0.0287 thresh=0.8, time wastes:0.1057 thresh=0.9, time wastes:0.4204
method 2: thresh=0.7, time wastes:0.0272 thresh=0.8, time wastes:0.1038 thresh=0.9, time wastes:0.4184
method 3: thresh=0.7, time wastes:0.0019 thresh=0.8, time wastes:0.0028 thresh=0.9, time wastes:0.0036
method 4: thresh=0.7, time wastes:0.0120 thresh=0.8, time wastes:0.0063 thresh=0.9, time wastes:0.0071
Reference: py-faster-rcnn: https://github.com/rbgirshick/py-faster-rcnn/tree/master/lib/nms