ResNet / Res2Net additions:

* ResNet torchscript compat
* output_stride arg supported to limit network stride via dilations (support for dilation added to Res2Net)
* allow activation layer to be changed via act_layer arg

timm/models/res2net.py

@@ -54,9 +54,8 @@ class Bottle2neck(nn.Module):
 
     def __init__(self, inplanes, planes, stride=1, downsample=None,
                  cardinality=1, base_width=26, scale=4, use_se=False,
-                 norm_layer=None, dilation=1, previous_dilation=1, **_):
+                 act_layer=nn.ReLU, norm_layer=None, dilation=1, previous_dilation=1, **_):
         super(Bottle2neck, self).__init__()
-        assert dilation == 1 and previous_dilation == 1  # FIXME support dilation
         self.scale = scale
         self.is_first = stride > 1 or downsample is not None
         self.num_scales = max(1, scale - 1)
@@ -71,18 +70,20 @@ class Bottle2neck(nn.Module):
         bns = []
         for i in range(self.num_scales):
             convs.append(nn.Conv2d(
-                width, width, kernel_size=3, stride=stride, padding=1, groups=cardinality, bias=False))
+                width, width, kernel_size=3, stride=stride, padding=dilation,
+                dilation=dilation, groups=cardinality, bias=False))
             bns.append(norm_layer(width))
         self.convs = nn.ModuleList(convs)
         self.bns = nn.ModuleList(bns)
         if self.is_first:
+            # FIXME this should probably have count_include_pad=False, but hurts original weights
             self.pool = nn.AvgPool2d(kernel_size=3, stride=stride, padding=1)
 
         self.conv3 = nn.Conv2d(width * scale, outplanes, kernel_size=1, bias=False)
         self.bn3 = norm_layer(outplanes)
         self.se = SEModule(outplanes, planes // 4) if use_se else None
 
-        self.relu = nn.ReLU(inplace=True)
+        self.relu = act_layer(inplace=True)
         self.downsample = downsample
 
     def forward(self, x):

timm/models/resnet.py

@@ -125,11 +125,12 @@ class SEModule(nn.Module):
 
 
 class BasicBlock(nn.Module):
+    __constants__ = ['se', 'downsample']  # for pre 1.4 torchscript compat
     expansion = 1
 
     def __init__(self, inplanes, planes, stride=1, downsample=None,
                  cardinality=1, base_width=64, use_se=False,
-                 reduce_first=1, dilation=1, previous_dilation=1, norm_layer=nn.BatchNorm2d):
+                 reduce_first=1, dilation=1, previous_dilation=1, act_layer=nn.ReLU, norm_layer=nn.BatchNorm2d):
         super(BasicBlock, self).__init__()
 
         assert cardinality == 1, 'BasicBlock only supports cardinality of 1'
@@ -141,12 +142,13 @@ class BasicBlock(nn.Module):
             inplanes, first_planes, kernel_size=3, stride=stride, padding=dilation,
             dilation=dilation, bias=False)
         self.bn1 = norm_layer(first_planes)
-        self.relu = nn.ReLU(inplace=True)
+        self.act1 = act_layer(inplace=True)
         self.conv2 = nn.Conv2d(
             first_planes, outplanes, kernel_size=3, padding=previous_dilation,
             dilation=previous_dilation, bias=False)
         self.bn2 = norm_layer(outplanes)
         self.se = SEModule(outplanes, planes // 4) if use_se else None
+        self.act2 = act_layer(inplace=True)
         self.downsample = downsample
         self.stride = stride
         self.dilation = dilation
@@ -156,7 +158,7 @@ class BasicBlock(nn.Module):
 
         out = self.conv1(x)
         out = self.bn1(out)
-        out = self.relu(out)
+        out = self.act1(out)
         out = self.conv2(out)
         out = self.bn2(out)
 
@@ -167,17 +169,18 @@ class BasicBlock(nn.Module):
             residual = self.downsample(x)
 
         out += residual
-        out = self.relu(out)
+        out = self.act2(out)
 
         return out
 
 
 class Bottleneck(nn.Module):
+    __constants__ = ['se', 'downsample']  # for pre 1.4 torchscript compat
     expansion = 4
 
     def __init__(self, inplanes, planes, stride=1, downsample=None,
                  cardinality=1, base_width=64, use_se=False,
-                 reduce_first=1, dilation=1, previous_dilation=1, norm_layer=nn.BatchNorm2d):
+                 reduce_first=1, dilation=1, previous_dilation=1, act_layer=nn.ReLU, norm_layer=nn.BatchNorm2d):
         super(Bottleneck, self).__init__()
 
         width = int(math.floor(planes * (base_width / 64)) * cardinality)
@@ -186,14 +189,16 @@ class Bottleneck(nn.Module):
 
         self.conv1 = nn.Conv2d(inplanes, first_planes, kernel_size=1, bias=False)
         self.bn1 = norm_layer(first_planes)
+        self.act1 = act_layer(inplace=True)
         self.conv2 = nn.Conv2d(
             first_planes, width, kernel_size=3, stride=stride,
             padding=dilation, dilation=dilation, groups=cardinality, bias=False)
         self.bn2 = norm_layer(width)
+        self.act2 = act_layer(inplace=True)
         self.conv3 = nn.Conv2d(width, outplanes, kernel_size=1, bias=False)
         self.bn3 = norm_layer(outplanes)
         self.se = SEModule(outplanes, planes // 4) if use_se else None
-        self.relu = nn.ReLU(inplace=True)
+        self.act3 = act_layer(inplace=True)
         self.downsample = downsample
         self.stride = stride
         self.dilation = dilation
@@ -203,11 +208,11 @@ class Bottleneck(nn.Module):
 
         out = self.conv1(x)
         out = self.bn1(out)
-        out = self.relu(out)
+        out = self.act1(out)
 
         out = self.conv2(out)
         out = self.bn2(out)
-        out = self.relu(out)
+        out = self.act2(out)
 
         out = self.conv3(out)
         out = self.bn3(out)
@@ -219,7 +224,7 @@ class Bottleneck(nn.Module):
             residual = self.downsample(x)
 
         out += residual
-        out = self.relu(out)
+        out = self.act3(out)
 
         return out
 
@@ -284,9 +289,10 @@ class ResNet(nn.Module):
         Kernel size of residual block downsampling path, 1x1 for most archs, 3x3 for senets
     avg_down : bool, default False
         Whether to use average pooling for projection skip connection between stages/downsample.
-    dilated : bool, default False
-        Applying dilation strategy to pretrained ResNet yielding a stride-8 model,
-        typically used in Semantic Segmentation.
+    output_stride : int, default 32
+        Set the output stride of the network, 32, 16, or 8. Typically used in segmentation.
+    act_layer : class, activation layer
+    norm_layer : class, normalization layer
     drop_rate : float, default 0.
         Dropout probability before classifier, for training
     global_pool : str, default 'avg'
@@ -294,8 +300,8 @@ class ResNet(nn.Module):
     """
     def __init__(self, block, layers, num_classes=1000, in_chans=3, use_se=False,
                  cardinality=1, base_width=64, stem_width=64, stem_type='',
-                 block_reduce_first=1, down_kernel_size=1, avg_down=False, dilated=False,
-                 norm_layer=nn.BatchNorm2d, drop_rate=0.0, global_pool='avg',
+                 block_reduce_first=1, down_kernel_size=1, avg_down=False, output_stride=32,
+                 act_layer=nn.ReLU, norm_layer=nn.BatchNorm2d, drop_rate=0.0, global_pool='avg',
                  zero_init_last_bn=True, block_args=None):
         block_args = block_args or dict()
         self.num_classes = num_classes
@@ -305,9 +311,9 @@ class ResNet(nn.Module):
         self.base_width = base_width
         self.drop_rate = drop_rate
         self.expansion = block.expansion
-        self.dilated = dilated
         super(ResNet, self).__init__()
 
+        # Stem
         if deep_stem:
             stem_chs_1 = stem_chs_2 = stem_width
             if 'tiered' in stem_type:
@@ -316,25 +322,37 @@ class ResNet(nn.Module):
             self.conv1 = nn.Sequential(*[
                 nn.Conv2d(in_chans, stem_chs_1, 3, stride=2, padding=1, bias=False),
                 norm_layer(stem_chs_1),
-                nn.ReLU(inplace=True),
+                act_layer(inplace=True),
                 nn.Conv2d(stem_chs_1, stem_chs_2, 3, stride=1, padding=1, bias=False),
                 norm_layer(stem_chs_2),
-                nn.ReLU(inplace=True),
+                act_layer(inplace=True),
                 nn.Conv2d(stem_chs_2, self.inplanes, 3, stride=1, padding=1, bias=False)])
         else:
             self.conv1 = nn.Conv2d(in_chans, self.inplanes, kernel_size=7, stride=2, padding=3, bias=False)
         self.bn1 = norm_layer(self.inplanes)
-        self.relu = nn.ReLU(inplace=True)
+        self.act1 = act_layer(inplace=True)
         self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
-        stride_3_4 = 1 if self.dilated else 2
-        dilation_3 = 2 if self.dilated else 1
-        dilation_4 = 4 if self.dilated else 1
-        largs = dict(use_se=use_se, reduce_first=block_reduce_first, norm_layer=norm_layer,
+
+        # Feature Blocks
+        channels, strides, dilations = [64, 128, 256, 512], [1, 2, 2, 2], [1] * 4
+        if output_stride == 16:
+            strides[3] = 1
+            dilations[3] = 2
+        elif output_stride == 8:
+            strides[2:4] = [1, 1]
+            dilations[2:4] = [2, 4]
+        else:
+            assert output_stride == 32
+        llargs = list(zip(channels, layers, strides, dilations))
+        lkwargs = dict(
+            use_se=use_se, reduce_first=block_reduce_first, act_layer=act_layer, norm_layer=norm_layer,
             avg_down=avg_down, down_kernel_size=down_kernel_size, **block_args)
-        self.layer1 = self._make_layer(block, 64, layers[0], stride=1, **largs)
-        self.layer2 = self._make_layer(block, 128, layers[1], stride=2, **largs)
-        self.layer3 = self._make_layer(block, 256, layers[2], stride=stride_3_4, dilation=dilation_3, **largs)
-        self.layer4 = self._make_layer(block, 512, layers[3], stride=stride_3_4, dilation=dilation_4, **largs)
+        self.layer1 = self._make_layer(block, *llargs[0], **lkwargs)
+        self.layer2 = self._make_layer(block, *llargs[1], **lkwargs)
+        self.layer3 = self._make_layer(block, *llargs[2], **lkwargs)
+        self.layer4 = self._make_layer(block, *llargs[3], **lkwargs)
+
+        # Head (Pooling and Classifier)
         self.global_pool = SelectAdaptivePool2d(pool_type=global_pool)
         self.num_features = 512 * block.expansion
         self.fc = nn.Linear(self.num_features * self.global_pool.feat_mult(), num_classes)
@@ -352,7 +370,8 @@ class ResNet(nn.Module):
                 nn.init.constant_(m.bias, 0.)
 
     def _make_layer(self, block, planes, blocks, stride=1, dilation=1, reduce_first=1,
-                    use_se=False, avg_down=False, down_kernel_size=1, norm_layer=nn.BatchNorm2d, **kwargs):
+                    use_se=False, avg_down=False, down_kernel_size=1, **kwargs):
+        norm_layer = kwargs.get('norm_layer')
         downsample = None
         down_kernel_size = 1 if stride == 1 and dilation == 1 else down_kernel_size
         if stride != 1 or self.inplanes != planes * block.expansion:
@@ -370,15 +389,15 @@ class ResNet(nn.Module):
             downsample = nn.Sequential(*downsample_layers)
 
         first_dilation = 1 if dilation in (1, 2) else 2
-        bargs = dict(
+        bkwargs = dict(
             cardinality=self.cardinality, base_width=self.base_width, reduce_first=reduce_first,
-            use_se=use_se, norm_layer=norm_layer, **kwargs)
+            use_se=use_se, **kwargs)
         layers = [block(
-            self.inplanes, planes, stride, downsample, dilation=first_dilation, previous_dilation=dilation, **bargs)]
+            self.inplanes, planes, stride, downsample, dilation=first_dilation, previous_dilation=dilation, **bkwargs)]
         self.inplanes = planes * block.expansion
         for i in range(1, blocks):
             layers.append(block(
-                self.inplanes, planes, dilation=dilation, previous_dilation=dilation, **bargs))
+                self.inplanes, planes, dilation=dilation, previous_dilation=dilation, **bkwargs))
 
         return nn.Sequential(*layers)
 
@@ -394,7 +413,7 @@ class ResNet(nn.Module):
     def forward_features(self, x):
         x = self.conv1(x)
         x = self.bn1(x)
-        x = self.relu(x)
+        x = self.act1(x)
         x = self.maxpool(x)
 
         x = self.layer1(x)