Add `SPPF()` layer (#4420)

* Add `SPPF()` layer

* Cleanup

* Add credit

models/common.py

@@ -161,7 +161,7 @@ class C3Ghost(C3):
 
 
 class SPP(nn.Module):
-    # Spatial pyramid pooling layer used in YOLOv3-SPP
+    # Spatial Pyramid Pooling (SPP) layer https://arxiv.org/abs/1406.4729
     def __init__(self, c1, c2, k=(5, 9, 13)):
         super().__init__()
         c_ = c1 // 2  # hidden channels
@@ -176,6 +176,24 @@ class SPP(nn.Module):
             return self.cv2(torch.cat([x] + [m(x) for m in self.m], 1))
 
 
+class SPPF(nn.Module):
+    # Spatial Pyramid Pooling - Fast (SPPF) layer for YOLOv5 by Glenn Jocher
+    def __init__(self, c1, c2, k=5):  # equivalent to SPP(k=(5, 9, 13))
+        super().__init__()
+        c_ = c1 // 2  # hidden channels
+        self.cv1 = Conv(c1, c_, 1, 1)
+        self.cv2 = Conv(c_ * 4, c2, 1, 1)
+        self.m = nn.MaxPool2d(kernel_size=k, stride=1, padding=k // 2)
+
+    def forward(self, x):
+        x = self.cv1(x)
+        with warnings.catch_warnings():
+            warnings.simplefilter('ignore')  # suppress torch 1.9.0 max_pool2d() warning
+            y1 = self.m(x)
+            y2 = self.m(y1)
+            return self.cv2(torch.cat([x, y1, y2, self.m(y2)], 1))
+
+
 class Focus(nn.Module):
     # Focus wh information into c-space
     def __init__(self, c1, c2, k=1, s=1, p=None, g=1, act=True):  # ch_in, ch_out, kernel, stride, padding, groups

models/yolo.py

@@ -237,8 +237,8 @@ def parse_model(d, ch):  # model_dict, input_channels(3)
                 pass
 
         n = n_ = max(round(n * gd), 1) if n > 1 else n  # depth gain
-        if m in [Conv, GhostConv, Bottleneck, GhostBottleneck, SPP, DWConv, MixConv2d, Focus, CrossConv, BottleneckCSP,
-                 C3, C3TR, C3SPP, C3Ghost]:
+        if m in [Conv, GhostConv, Bottleneck, GhostBottleneck, SPP, SPPF, DWConv, MixConv2d, Focus, CrossConv,
+                 BottleneckCSP, C3, C3TR, C3SPP, C3Ghost]:
             c1, c2 = ch[f], args[0]
             if c2 != no:  # if not output
                 c2 = make_divisible(c2 * gw, 8)
@@ -279,6 +279,7 @@ if __name__ == '__main__':
     parser = argparse.ArgumentParser()
     parser.add_argument('--cfg', type=str, default='yolov5s.yaml', help='model.yaml')
     parser.add_argument('--device', default='', help='cuda device, i.e. 0 or 0,1,2,3 or cpu')
+    parser.add_argument('--profile', action='store_true', help='profile model speed')
     opt = parser.parse_args()
     opt.cfg = check_file(opt.cfg)  # check file
     set_logging()
@@ -289,8 +290,9 @@ if __name__ == '__main__':
     model.train()
 
     # Profile
-    # img = torch.rand(8 if torch.cuda.is_available() else 1, 3, 320, 320).to(device)
-    # y = model(img, profile=True)
+    if opt.profile:
+        img = torch.rand(8 if torch.cuda.is_available() else 1, 3, 640, 640).to(device)
+        y = model(img, profile=True)
 
     # Tensorboard (not working https://github.com/ultralytics/yolov5/issues/2898)
     # from torch.utils.tensorboard import SummaryWriter