Add ResNeXt

mmcls/models/backbones/__init__.py

@@ -1,3 +1,4 @@
 from .resnet import ResNet, ResNetV1d
+from .resnext import ResNeXt
 
-__all__ = ['ResNet', 'ResNetV1d']
+__all__ = ['ResNet', 'ResNeXt', 'ResNetV1d']

mmcls/models/backbones/resnext.py

@@ -0,0 +1,132 @@
+import math
+
+from mmcv.cnn import build_conv_layer, build_norm_layer
+
+from ..builder import BACKBONES
+from .resnet import Bottleneck as _Bottleneck
+from .resnet import ResLayer, ResNet
+
+
+class Bottleneck(_Bottleneck):
+    """Bottleneck block for ResNeXt.
+
+    Args:
+        inplanes (int): inplanes of block.
+        planes (int): planes of block.
+        groups (int): group of convolution.
+        base_width (int): Base width of resnext.
+        base_channels (int): Number of base channels of hidden layer.
+        stride (int): stride of the block. Default: 1
+        dilation (int): dilation of convolution. Default: 1
+        downsample (nn.Module): downsample operation on identity branch.
+            Default: None
+        style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two
+            layer is the 3x3 conv layer, otherwise the stride-two layer is
+            the first 1x1 conv layer.
+        conv_cfg (dict): dictionary to construct and config conv layer.
+            Default: None
+        norm_cfg (dict): dictionary to construct and config norm layer.
+            Default: dict(type='BN')
+        with_cp (bool): Use checkpoint or not. Using checkpoint will save some
+            memory while slowing down the training speed.
+    """
+
+    expansion = 4
+
+    def __init__(self,
+                 inplanes,
+                 planes,
+                 groups=1,
+                 base_width=4,
+                 base_channels=64,
+                 **kwargs):
+        super(Bottleneck, self).__init__(inplanes, planes, **kwargs)
+
+        if groups == 1:
+            width = self.planes
+        else:
+            width = math.floor(self.planes *
+                               (base_width / base_channels)) * groups
+
+        self.norm1_name, norm1 = build_norm_layer(
+            self.norm_cfg, width, postfix=1)
+        self.norm2_name, norm2 = build_norm_layer(
+            self.norm_cfg, width, postfix=2)
+        self.norm3_name, norm3 = build_norm_layer(
+            self.norm_cfg, self.planes * self.expansion, postfix=3)
+
+        self.conv1 = build_conv_layer(
+            self.conv_cfg,
+            self.inplanes,
+            width,
+            kernel_size=1,
+            stride=self.conv1_stride,
+            bias=False)
+        self.add_module(self.norm1_name, norm1)
+        self.conv2 = build_conv_layer(
+            self.conv_cfg,
+            width,
+            width,
+            kernel_size=3,
+            stride=self.conv2_stride,
+            padding=self.dilation,
+            dilation=self.dilation,
+            groups=groups,
+            bias=False)
+
+        self.add_module(self.norm2_name, norm2)
+        self.conv3 = build_conv_layer(
+            self.conv_cfg,
+            width,
+            self.planes * self.expansion,
+            kernel_size=1,
+            bias=False)
+        self.add_module(self.norm3_name, norm3)
+
+
+@BACKBONES.register_module()
+class ResNeXt(ResNet):
+    """ResNeXt backbone.
+
+    Args:
+        groups (int): Group of resnext.
+        base_width (int): Base width of resnext.
+        depth (int): Depth of resnext, from {50, 101, 152}.
+        in_channels (int): Number of input image channels. Default: 3.
+        base_channels (int): Number of base channels of hidden layer.
+        num_stages (int): Resnet stages. Default: 4.
+        strides (Sequence[int]): Strides of the first block of each stage.
+        dilations (Sequence[int]): Dilation of each stage.
+        out_indices (Sequence[int]): Output from which stages.
+        style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two
+            layer is the 3x3 conv layer, otherwise the stride-two layer is
+            the first 1x1 conv layer.
+        frozen_stages (int): Stages to be frozen (all param fixed). -1 means
+            not freezing any parameters.
+        norm_cfg (dict): dictionary to construct and config norm layer.
+        norm_eval (bool): Whether to set norm layers to eval mode, namely,
+            freeze running stats (mean and var). Note: Effect on Batch Norm
+            and its variants only.
+        with_cp (bool): Use checkpoint or not. Using checkpoint will save some
+            memory while slowing down the training speed.
+        zero_init_residual (bool): whether to use zero init for last norm layer
+            in resblocks to let them behave as identity.
+    """
+
+    arch_settings = {
+        50: (Bottleneck, (3, 4, 6, 3)),
+        101: (Bottleneck, (3, 4, 23, 3)),
+        152: (Bottleneck, (3, 8, 36, 3))
+    }
+
+    def __init__(self, groups=1, base_width=4, **kwargs):
+        self.groups = groups
+        self.base_width = base_width
+        super(ResNeXt, self).__init__(**kwargs)
+
+    def make_res_layer(self, **kwargs):
+        return ResLayer(
+            groups=self.groups,
+            base_width=self.base_width,
+            base_channels=self.base_channels,
+            **kwargs)

tests/test_backbones/test_resnext.py

@@ -0,0 +1,66 @@
+import pytest
+import torch
+
+from mmcls.models.backbones import ResNeXt
+from mmcls.models.backbones.resnext import Bottleneck as BottleneckX
+
+
+def is_block(modules):
+    """Check if is ResNeXt building block."""
+    if isinstance(modules, (BottleneckX)):
+        return True
+    return False
+
+
+def test_resnext_bottleneck():
+    with pytest.raises(AssertionError):
+        # Style must be in ['pytorch', 'caffe']
+        BottleneckX(64, 64, groups=32, base_width=4, style='tensorflow')
+
+    # Test ResNeXt Bottleneck structure
+    block = BottleneckX(
+        64, 64, groups=32, base_width=4, stride=2, style='pytorch')
+    assert block.conv2.stride == (2, 2)
+    assert block.conv2.groups == 32
+    assert block.conv2.out_channels == 128
+
+    # Test ResNeXt Bottleneck forward
+    block = BottleneckX(64, 16, groups=32, base_width=4)
+    x = torch.randn(1, 64, 56, 56)
+    x_out = block(x)
+    assert x_out.shape == torch.Size([1, 64, 56, 56])
+
+
+def test_resnext_backbone():
+    with pytest.raises(KeyError):
+        # ResNeXt depth should be in [50, 101, 152]
+        ResNeXt(depth=18)
+
+    # Test ResNeXt with group 32, base_width 4
+    model = ResNeXt(
+        depth=50, groups=32, base_width=4, out_indices=(0, 1, 2, 3))
+    for m in model.modules():
+        if is_block(m):
+            assert m.conv2.groups == 32
+    model.init_weights()
+    model.train()
+
+    imgs = torch.randn(1, 3, 224, 224)
+    feat = model(imgs)
+    assert len(feat) == 4
+    assert feat[0].shape == torch.Size([1, 256, 56, 56])
+    assert feat[1].shape == torch.Size([1, 512, 28, 28])
+    assert feat[2].shape == torch.Size([1, 1024, 14, 14])
+    assert feat[3].shape == torch.Size([1, 2048, 7, 7])
+
+    # Test ResNeXt with group 32, base_width 4 and layers 3 out forward
+    model = ResNeXt(depth=50, groups=32, base_width=4, out_indices=(3, ))
+    for m in model.modules():
+        if is_block(m):
+            assert m.conv2.groups == 32
+    model.init_weights()
+    model.train()
+
+    imgs = torch.randn(1, 3, 224, 224)
+    feat = model(imgs)
+    assert feat.shape == torch.Size([1, 2048, 7, 7])