shufflenetv2.py
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'''ShuffleNetV2 in PyTorch.
See the paper "ShuffleNet V2: Practical Guidelines for Efficient CNN Architecture Design" for more details.
'''
import torch
import torch.nn as nn
import torch.nn.functional as F
class ShuffleBlock(nn.Module):
def __init__(self, groups=2):
super(ShuffleBlock, self).__init__()
self.groups = groups
def forward(self, x):
'''Channel shuffle: [N,C,H,W] -> [N,g,C/g,H,W] -> [N,C/g,g,H,w] -> [N,C,H,W]'''
N, C, H, W = x.size()
g = self.groups
return x.view(N, g, C//g, H, W).permute(0, 2, 1, 3, 4).reshape(N, C, H, W)
class SplitBlock(nn.Module):
def __init__(self, ratio):
super(SplitBlock, self).__init__()
self.ratio = ratio
def forward(self, x):
c = int(x.size(1) * self.ratio)
return x[:, :c, :, :], x[:, c:, :, :]
class BasicBlock(nn.Module):
def __init__(self, in_channels, split_ratio=0.5):
super(BasicBlock, self).__init__()
self.split = SplitBlock(split_ratio)
in_channels = int(in_channels * split_ratio)
self.conv1 = nn.Conv2d(in_channels, in_channels,
kernel_size=1, bias=False)
self.bn1 = nn.BatchNorm2d(in_channels)
self.conv2 = nn.Conv2d(in_channels, in_channels,
kernel_size=3, stride=1, padding=1, groups=in_channels, bias=False)
self.bn2 = nn.BatchNorm2d(in_channels)
self.conv3 = nn.Conv2d(in_channels, in_channels,
kernel_size=1, bias=False)
self.bn3 = nn.BatchNorm2d(in_channels)
self.shuffle = ShuffleBlock()
def forward(self, x):
x1, x2 = self.split(x)
out = F.relu(self.bn1(self.conv1(x2)))
out = self.bn2(self.conv2(out))
out = F.relu(self.bn3(self.conv3(out)))
out = torch.cat([x1, out], 1)
out = self.shuffle(out)
return out
class DownBlock(nn.Module):
def __init__(self, in_channels, out_channels):
super(DownBlock, self).__init__()
mid_channels = out_channels // 2
# left
self.conv1 = nn.Conv2d(in_channels, in_channels,
kernel_size=3, stride=2, padding=1, groups=in_channels, bias=False)
self.bn1 = nn.BatchNorm2d(in_channels)
self.conv2 = nn.Conv2d(in_channels, mid_channels,
kernel_size=1, bias=False)
self.bn2 = nn.BatchNorm2d(mid_channels)
# right
self.conv3 = nn.Conv2d(in_channels, mid_channels,
kernel_size=1, bias=False)
self.bn3 = nn.BatchNorm2d(mid_channels)
self.conv4 = nn.Conv2d(mid_channels, mid_channels,
kernel_size=3, stride=2, padding=1, groups=mid_channels, bias=False)
self.bn4 = nn.BatchNorm2d(mid_channels)
self.conv5 = nn.Conv2d(mid_channels, mid_channels,
kernel_size=1, bias=False)
self.bn5 = nn.BatchNorm2d(mid_channels)
self.shuffle = ShuffleBlock()
def forward(self, x):
# left
out1 = self.bn1(self.conv1(x))
out1 = F.relu(self.bn2(self.conv2(out1)))
# right
out2 = F.relu(self.bn3(self.conv3(x)))
out2 = self.bn4(self.conv4(out2))
out2 = F.relu(self.bn5(self.conv5(out2)))
# concat
out = torch.cat([out1, out2], 1)
out = self.shuffle(out)
return out
class ShuffleNetV2(nn.Module):
def __init__(self, net_size):
super(ShuffleNetV2, self).__init__()
out_channels = configs[net_size]['out_channels']
num_blocks = configs[net_size]['num_blocks']
self.conv1 = nn.Conv2d(3, 24, kernel_size=3,
stride=1, padding=1, bias=False)
self.bn1 = nn.BatchNorm2d(24)
self.in_channels = 24
self.layer1 = self._make_layer(out_channels[0], num_blocks[0])
self.layer2 = self._make_layer(out_channels[1], num_blocks[1])
self.layer3 = self._make_layer(out_channels[2], num_blocks[2])
self.conv2 = nn.Conv2d(out_channels[2], out_channels[3],
kernel_size=1, stride=1, padding=0, bias=False)
self.bn2 = nn.BatchNorm2d(out_channels[3])
self.linear = nn.Linear(out_channels[3], 10)
def _make_layer(self, out_channels, num_blocks):
layers = [DownBlock(self.in_channels, out_channels)]
for i in range(num_blocks):
layers.append(BasicBlock(out_channels))
self.in_channels = out_channels
return nn.Sequential(*layers)
def forward(self, x):
out = F.relu(self.bn1(self.conv1(x)))
# out = F.max_pool2d(out, 3, stride=2, padding=1)
out = self.layer1(out)
out = self.layer2(out)
out = self.layer3(out)
out = F.relu(self.bn2(self.conv2(out)))
out = F.avg_pool2d(out, 4)
out = out.view(out.size(0), -1)
out = self.linear(out)
return out
configs = {
0.5: {
'out_channels': (48, 96, 192, 1024),
'num_blocks': (3, 7, 3)
},
1: {
'out_channels': (116, 232, 464, 1024),
'num_blocks': (3, 7, 3)
},
1.5: {
'out_channels': (176, 352, 704, 1024),
'num_blocks': (3, 7, 3)
},
2: {
'out_channels': (224, 488, 976, 2048),
'num_blocks': (3, 7, 3)
}
}
def test():
net = ShuffleNetV2(net_size=0.5)
x = torch.randn(3, 3, 32, 32)
y = net(x)
print(y.shape)
# test()