NMS implementation

[Wok]

I see that you use a custom Python implementation for NMS.

facexlib/facexlib/detection/retinaface_utils.py

Lines 38 to 66 in 206e0cc

 def py_cpu_nms(dets, thresh): 
     """Pure Python NMS baseline.""" 
     x1 = dets[:, 0] 
     y1 = dets[:, 1] 
     x2 = dets[:, 2] 
     y2 = dets[:, 3] 
     scores = dets[:, 4] 
  
     areas = (x2 - x1 + 1) * (y2 - y1 + 1) 
     order = scores.argsort()[::-1] 
  
     keep = [] 
     while order.size > 0: 
         i = order[0] 
         keep.append(i) 
         xx1 = np.maximum(x1[i], x1[order[1:]]) 
         yy1 = np.maximum(y1[i], y1[order[1:]]) 
         xx2 = np.minimum(x2[i], x2[order[1:]]) 
         yy2 = np.minimum(y2[i], y2[order[1:]]) 
  
         w = np.maximum(0.0, xx2 - xx1 + 1) 
         h = np.maximum(0.0, yy2 - yy1 + 1) 
         inter = w * h 
         ovr = inter / (areas[i] + areas[order[1:]] - inter) 
  
         inds = np.where(ovr <= thresh)[0] 
         order = order[inds + 1] 
  
     return keep 

Moreover, the requirements of this repository include torchvision:

facexlib/requirements.txt

Line 9 in 206e0cc

 torchvision 

I wonder whether it would be beneficial to use torchvision's implementation of NMS instead. cf. torchvision.ops.nms
I had this idea after a quick discussion in another repository: ternaus/retinaface#23 (comment)

[Xintao]

@woctezuma
Thanks for your suggestion.
It is a good improvement.
I am busy these days and may improve it later.

It would be great if you can help it and open a PR 😃