densenet.py

import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.autograd import Variable


import math
import numpy as np

class Bottleneck(nn.Module):
    def __init__(self, nChannels, growthRate):
        super(Bottleneck, self).__init__()
        interChannels = 4*growthRate
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, interChannels, kernel_size=1, bias=False)
        self.bn2 = nn.BatchNorm2d(interChannels)
        self.conv2 = nn.Conv2d(interChannels, growthRate, kernel_size=3, padding=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = self.conv2(F.relu(self.bn2(out)))
        out = torch.cat((x, out), 1)
        return out

class SingleLayer(nn.Module):
    def __init__(self, nChannels, growthRate):
        super(SingleLayer, self).__init__()
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, growthRate, kernel_size=3, padding=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = torch.cat((x, out), 1)
        return out

class Transition(nn.Module):
    def __init__(self, nChannels, nOutChannels):
        super(Transition, self).__init__()
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, nOutChannels, kernel_size=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = F.avg_pool2d(out, 2)
        return out


class DenseNet(nn.Module):
    def __init__(self, input_shape, growthRate, depth, reduction, nClasses, bottleneck):
        super(DenseNet, self).__init__()

        nDenseBlocks = (depth-4) // 3
        if bottleneck:
            nDenseBlocks //= 2

        nChannels = 2*growthRate
        self.conv1 = nn.Conv2d(1, nChannels, kernel_size=3, padding=1, bias=False)
        self.dense1 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks*growthRate
        nOutChannels = int(math.floor(nChannels*reduction))
        self.trans1 = Transition(nChannels, nOutChannels)

        nChannels = nOutChannels
        self.dense2 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks*growthRate
        nOutChannels = int(math.floor(nChannels*reduction))
        self.trans2 = Transition(nChannels, nOutChannels)

        nChannels = nOutChannels
        self.dense3 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks*growthRate

        self.bn1 = nn.BatchNorm2d(nChannels)

        self.features = nn.Sequential(
            self.conv1,
            self.dense1,
            self.trans1,
            self.dense2,
            self.trans2,
            self.dense3,
            self.bn1,
            nn.ReLU(),
            nn.AvgPool2d(8),
        )

        self.n_flat_features = self._get_flat_features(input_shape, self.features)

        self.fc = nn.Linear(self.n_flat_features, nClasses)

        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))
            elif isinstance(m, nn.BatchNorm2d):
                m.weight.data.fill_(1)
                m.bias.data.zero_()
            elif isinstance(m, nn.Linear):
                m.bias.data.zero_()

    def _make_dense(self, nChannels, growthRate, nDenseBlocks, bottleneck):
        layers = []
        for i in range(int(nDenseBlocks)):
            if bottleneck:
                layers.append(Bottleneck(nChannels, growthRate))
            else:
                layers.append(SingleLayer(nChannels, growthRate))
            nChannels += growthRate
        return nn.Sequential(*layers)

    def _get_flat_features(self, image_shape, features):
        f = features(torch.ones(1,*image_shape))
        return int(np.prod(f.size()))

    def forward(self, x):
        # print('input forward:', x.shape)
        out = self.features(x)
        out = out.view(out.size(0), -1)
        out = self.fc(out)
        return out