import torch.nn as nn import math def conv_bn(inp, oup, stride): return nn.Sequential( nn.Conv2d(inp, oup, 3, stride, 1, bias=False), nn.BatchNorm2d(oup), nn.ReLU6(inplace=True) ) def conv_1x1_bn(inp, oup): return nn.Sequential( nn.Conv2d(inp, oup, 1, 1, 0, bias=False), nn.BatchNorm2d(oup), nn.ReLU6(inplace=True) ) class InvertedResidual(nn.Module): def __init__(self, inp, oup, stride, expand_ratio): super(InvertedResidual, self).__init__() self.stride = stride assert stride in [1, 2] hidden_dim = round(inp * expand_ratio) self.use_res_connect = self.stride == 1 and inp == oup if expand_ratio == 1: self.conv = nn.Sequential( # dw nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False), nn.BatchNorm2d(hidden_dim), nn.ReLU6(inplace=True), # pw-linear nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False), nn.BatchNorm2d(oup), ) else: self.conv = nn.Sequential( # pw nn.Conv2d(inp, hidden_dim, 1, 1, 0, bias=False), nn.BatchNorm2d(hidden_dim), nn.ReLU6(inplace=True), # dw nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False), nn.BatchNorm2d(hidden_dim), nn.ReLU6(inplace=True), # pw-linear nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False), nn.BatchNorm2d(oup), ) def forward(self, x): if self.use_res_connect: return x + self.conv(x) else: return self.conv(x) class MobileNetV2(nn.Module): def __init__(self, n_class=1000, input_size=224, width_mult=1.): super(MobileNetV2, self).__init__() block = InvertedResidual input_channel = 32 last_channel = 1280 interverted_residual_setting = [ # t, c, n, s [1, 16, 1, 1], [6, 24, 2, 2], [6, 32, 3, 2], [6, 64, 4, 2], [6, 96, 3, 1], [6, 160, 3, 2], [6, 320, 1, 1], ] # building first layer assert input_size % 32 == 0 input_channel = int(input_channel * width_mult) self.last_channel = int(last_channel * width_mult) if width_mult > 1.0 else last_channel self.features = [conv_bn(3, input_channel, 2)] # building inverted residual blocks for t, c, n, s in interverted_residual_setting: output_channel = int(c * width_mult) for i in range(n): if i == 0: self.features.append(block(input_channel, output_channel, s, expand_ratio=t)) else: self.features.append(block(input_channel, output_channel, 1, expand_ratio=t)) input_channel = output_channel # building last several layers self.features.append(conv_1x1_bn(input_channel, self.last_channel)) # make it nn.Sequential self.features = nn.Sequential(*self.features) # building classifier self.classifier = nn.Sequential( nn.Dropout(0.2), nn.Linear(self.last_channel, n_class), ) self._initialize_weights() def forward(self, x): x = self.features(x) x = x.mean(3).mean(2) x = self.classifier(x) return x def _initialize_weights(self): for m in self.modules(): if isinstance(m, nn.Conv2d): n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels m.weight.data.normal_(0, math.sqrt(2. / n)) if m.bias is not None: m.bias.data.zero_() elif isinstance(m, nn.BatchNorm2d): m.weight.data.fill_(1) m.bias.data.zero_() elif isinstance(m, nn.Linear): n = m.weight.size(1) m.weight.data.normal_(0, 0.01) m.bias.data.zero_()