GoogLenet网络详解

GoogLenet

VGG在2014年由牛津大学著名研究组vGG (Visual Geometry Group)提出，斩获该年lmageNet竞赛中Localization Task (定位任务)第一名和 Classification Task (分类任务)第二名。Classification Task (分类任务)的第一名则是GoogleNet 。GoogleNet是Google研发的深度网络结构，之所以叫“GoogLeNet”，是为了向“LeNet”致敬。

GoogLenet网络亮点

1.引入了Inception结构（融合不同尺度的特征信息)
2.使用1x1的卷积核进行降维以及映射处理
3.添加两个辅助分类器帮助训练
4.丢弃全连接层，使用平均池化层(大大减少模型参数)

Inception结构

Inception Module基本组成结构有四个成分。1x1卷积，3x3卷积，5x5卷积，3x3最大池化。最后对四个成分运算结果进行通道上组合，这就是Naive Inception(上图a)的核心思想：利用不同大小的卷积核实现不同尺度的感知，最后进行融合，可以得到图像更好的表征。注意，每个分支得到的特征矩阵高和宽必须相同。但是Naive Inception有两个非常严重的问题：首先，所有卷积层直接和前一层输入的数据对接，所以卷积层中的计算量会很大；其次，在这个单元中使用的最大池化层保留了输入数据的特征图的深度，所以在最后进行合并时，总的输出的特征图的深度只会增加，这样增加了该单元之后的网络结构的计算量。所以这里使用1x1 卷积核主要目的是进行压缩降维，减少参数量，也就是上图b，从而让网络更深、更宽，更好的提取特征，这种思想也称为Pointwise Conv，简称PW。

小算一下，假设输入图像的通道是512，使用64个5x5的卷积核进行卷积，不使用1x1卷积核降维需要的参数为512x64x5x5=819200。若使用24个1x1的卷积核降维，得到图像通道为24，再与65个卷积核进行卷积，此时需要的参数为512x24x1x1+24x65x5x5=50688。

辅助分类器

根据实验数据，发现神经网络的中间层也具有很强的识别能力，为了利用中间层抽象的特征，在某些中间层中添加含有多层的分类器。如下图所示，红色边框内部代表添加的辅助分类器。GoogLeNet中共增加了两个辅助的softmax分支，作用有两点，一是为了避免梯度消失，用于向前传导梯度。反向传播时如果有一层求导为0，链式求导结果则为0。二是将中间某一层输出用作分类，起到模型融合作用。最后的loss=loss_2 + 0.3 * loss_1 + 0.3 * loss_0。实际测试时，这两个辅助softmax分支会被去掉。

1.平均池化层

窗口大小为5×5，步幅为3，结果是(4a)的输出为4×4×512， (4d)阶段的输出为4×4×528。

2.卷积层

128个1×1卷积核进行卷积(降维)，使用ReLU激活函数。

3.全连接层

1024个结点的全连接层，同样使用ReLU激活函数。

4.dropout

dropout，以70%比例随机失活神经元。

5.softmax

通过softmax输出1000个预测结果。

GoogLenet网络结构

用表格的形式表示GoogLeNet的网络结构如下所示：

Inception结构的参数怎么看呢？在下面这张图标注出来了。

下面就来详细介绍一下GoogLeNet的模型结构。

1.卷积层

输入图像为224x224x3，卷积核大小7x7，步长为2，padding为3，输出通道数64，输出大小为(224-7+3x2)/2+1=112.5(向下取整)=112，输出为112x112x64，卷积后进行ReLU操作。

2.最大池化层

窗口大小3x3，步长为2，输出大小为((112 -3)/2)+1=55.5(向上取整)=56，输出为56x56x64。

3.两层卷积层

第一层：用64个1x1的卷积核（3x3卷积核之前的降维）将输入的特征图（56x56x64）变为56x56x64，然后进行ReLU操作。

第二层：用卷积核大小3x3，步长为1，padding为1，输出通道数192，进行卷积运算，输出大小为(56-3+1x2)/1+1=56，输出为56x56x192，然后进行ReLU操作。

4. 最大池化层

窗口大小3x3，步长为2，输出通道数192，输出为((56 - 3)/2)+1=27.5(向上取整)=28，输出特征图维度为28x28x192。

5.Inception 3a

1.使用64个1x1的卷积核，卷积后输出为28x28x64，然后RuLU操作。
2.96个1x1的卷积核（3x3卷积核之前的降维）卷积后输出为28x28x96，进行ReLU计算，再进行128个3x3的卷积，输出28x28x128。
3.16个1x1的卷积核（5x5卷积核之前的降维）卷积后输出为28x28x16，进行ReLU计算，再进行32个5x5的卷积，输出28x28x32。
4.最大池化层，窗口大小3x3，输出28x28x192，然后进行32个1x1的卷积，输出28x28x32.。

6.Inception 3b

7.最大池化层

8.Inception 4a 4b 4c 4d 4e

9.最大池化层

10.Inception 5a 5b

11.输出层

GoogLeNet采用平均池化层，得到高和宽均为1的卷积层；然后dropout，以40%随机失活神经元；输出层激活函数采用的是softmax。

GoogLenet实现

Inception实现

class Inception(nn.Module):
    def __init__(self, in_channels, ch1x1, ch3x3red, ch3x3, ch5x5red, ch5x5, pool_proj):
        super(Inception, self).__init__()

        self.branch1 = BasicConv2d(in_channels, ch1x1, kernel_size=1)

        self.branch2 = nn.Sequential(
            BasicConv2d(in_channels, ch3x3red, kernel_size=1),
            BasicConv2d(ch3x3red, ch3x3, kernel_size=3, padding=1)   # 保证输出大小等于输入大小
        )

        self.branch3 = nn.Sequential(
            BasicConv2d(in_channels, ch5x5red, kernel_size=1),
            # 在官方的实现中，其实是3x3的kernel并不是5x5，这里我也懒得改了，具体可以参考下面的issue
            # Please see https://github.com/pytorch/vision/issues/906 for details.
            BasicConv2d(ch5x5red, ch5x5, kernel_size=5, padding=2)   # 保证输出大小等于输入大小
        )

        self.branch4 = nn.Sequential(
            nn.MaxPool2d(kernel_size=3, stride=1, padding=1),
            BasicConv2d(in_channels, pool_proj, kernel_size=1)
        )

    def forward(self, x):
        branch1 = self.branch1(x)
        branch2 = self.branch2(x)
        branch3 = self.branch3(x)
        branch4 = self.branch4(x)

        outputs = [branch1, branch2, branch3, branch4]
        return torch.cat(outputs, 1)
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GoogLenet实现

import torch.nn as nn
import torch
import torch.nn.functional as F


class GoogLeNet(nn.Module):
    def __init__(self, num_classes=1000, aux_logits=True, init_weights=False):
        super(GoogLeNet, self).__init__()
        self.aux_logits = aux_logits

        self.conv1 = BasicConv2d(3, 64, kernel_size=7, stride=2, padding=3)
        self.maxpool1 = nn.MaxPool2d(3, stride=2, ceil_mode=True)

        self.conv2 = BasicConv2d(64, 64, kernel_size=1)
        self.conv3 = BasicConv2d(64, 192, kernel_size=3, padding=1)
        self.maxpool2 = nn.MaxPool2d(3, stride=2, ceil_mode=True)

        self.inception3a = Inception(192, 64, 96, 128, 16, 32, 32)
        self.inception3b = Inception(256, 128, 128, 192, 32, 96, 64)
        self.maxpool3 = nn.MaxPool2d(3, stride=2, ceil_mode=True)

        self.inception4a = Inception(480, 192, 96, 208, 16, 48, 64)
        self.inception4b = Inception(512, 160, 112, 224, 24, 64, 64)
        self.inception4c = Inception(512, 128, 128, 256, 24, 64, 64)
        self.inception4d = Inception(512, 112, 144, 288, 32, 64, 64)
        self.inception4e = Inception(528, 256, 160, 320, 32, 128, 128)
        self.maxpool4 = nn.MaxPool2d(3, stride=2, ceil_mode=True)

        self.inception5a = Inception(832, 256, 160, 320, 32, 128, 128)
        self.inception5b = Inception(832, 384, 192, 384, 48, 128, 128)

        if self.aux_logits:
            self.aux1 = InceptionAux(512, num_classes)
            self.aux2 = InceptionAux(528, num_classes)

        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        self.dropout = nn.Dropout(0.4)
        self.fc = nn.Linear(1024, num_classes)
        if init_weights:
            self._initialize_weights()

    def forward(self, x):
        # N x 3 x 224 x 224
        x = self.conv1(x)
        # N x 64 x 112 x 112
        x = self.maxpool1(x)
        # N x 64 x 56 x 56
        x = self.conv2(x)
        # N x 64 x 56 x 56
        x = self.conv3(x)
        # N x 192 x 56 x 56
        x = self.maxpool2(x)

        # N x 192 x 28 x 28
        x = self.inception3a(x)
        # N x 256 x 28 x 28
        x = self.inception3b(x)
        # N x 480 x 28 x 28
        x = self.maxpool3(x)
        # N x 480 x 14 x 14
        x = self.inception4a(x)
        # N x 512 x 14 x 14
        if self.training and self.aux_logits:    # eval model lose this layer
            aux1 = self.aux1(x)

        x = self.inception4b(x)
        # N x 512 x 14 x 14
        x = self.inception4c(x)
        # N x 512 x 14 x 14
        x = self.inception4d(x)
        # N x 528 x 14 x 14
        if self.training and self.aux_logits:    # eval model lose this layer
            aux2 = self.aux2(x)

        x = self.inception4e(x)
        # N x 832 x 14 x 14
        x = self.maxpool4(x)
        # N x 832 x 7 x 7
        x = self.inception5a(x)
        # N x 832 x 7 x 7
        x = self.inception5b(x)
        # N x 1024 x 7 x 7

        x = self.avgpool(x)
        # N x 1024 x 1 x 1
        x = torch.flatten(x, 1)
        # N x 1024
        x = self.dropout(x)
        x = self.fc(x)
        # N x 1000 (num_classes)
        if self.training and self.aux_logits:   # eval model lose this layer
            return x, aux2, aux1
        return x

    def _initialize_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
                if m.bias is not None:
                    nn.init.constant_(m.bias, 0)
            elif isinstance(m, nn.Linear):
                nn.init.normal_(m.weight, 0, 0.01)
                nn.init.constant_(m.bias, 0)


class Inception(nn.Module):
    def __init__(self, in_channels, ch1x1, ch3x3red, ch3x3, ch5x5red, ch5x5, pool_proj):
        super(Inception, self).__init__()

        self.branch1 = BasicConv2d(in_channels, ch1x1, kernel_size=1)

        self.branch2 = nn.Sequential(
            BasicConv2d(in_channels, ch3x3red, kernel_size=1),
            BasicConv2d(ch3x3red, ch3x3, kernel_size=3, padding=1)   # 保证输出大小等于输入大小
        )

        self.branch3 = nn.Sequential(
            BasicConv2d(in_channels, ch5x5red, kernel_size=1),
            # 在官方的实现中，其实是3x3的kernel并不是5x5，这里我也懒得改了，具体可以参考下面的issue
            # Please see https://github.com/pytorch/vision/issues/906 for details.
            BasicConv2d(ch5x5red, ch5x5, kernel_size=5, padding=2)   # 保证输出大小等于输入大小
        )

        self.branch4 = nn.Sequential(
            nn.MaxPool2d(kernel_size=3, stride=1, padding=1),
            BasicConv2d(in_channels, pool_proj, kernel_size=1)
        )

    def forward(self, x):
        branch1 = self.branch1(x)
        branch2 = self.branch2(x)
        branch3 = self.branch3(x)
        branch4 = self.branch4(x)

        outputs = [branch1, branch2, branch3, branch4]
        return torch.cat(outputs, 1)


class InceptionAux(nn.Module):
    def __init__(self, in_channels, num_classes):
        super(InceptionAux, self).__init__()
        self.averagePool = nn.AvgPool2d(kernel_size=5, stride=3)
        self.conv = BasicConv2d(in_channels, 128, kernel_size=1)  # output[batch, 128, 4, 4]

        self.fc1 = nn.Linear(2048, 1024)
        self.fc2 = nn.Linear(1024, num_classes)

    def forward(self, x):
        # aux1: N x 512 x 14 x 14, aux2: N x 528 x 14 x 14
        x = self.averagePool(x)
        # aux1: N x 512 x 4 x 4, aux2: N x 528 x 4 x 4
        x = self.conv(x)
        # N x 128 x 4 x 4
        x = torch.flatten(x, 1)
        x = F.dropout(x, 0.5, training=self.training)
        # N x 2048
        x = F.relu(self.fc1(x), inplace=True)
        x = F.dropout(x, 0.5, training=self.training)
        # N x 1024
        x = self.fc2(x)
        # N x num_classes
        return x


class BasicConv2d(nn.Module):
    def __init__(self, in_channels, out_channels, **kwargs):
        super(BasicConv2d, self).__init__()
        self.conv = nn.Conv2d(in_channels, out_channels, **kwargs)
        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        x = self.conv(x)
        x = self.relu(x)
        return x

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训练模型

import os
import sys
import json

import torch
import torch.nn as nn
from torchvision import transforms, datasets
import torch.optim as optim
from tqdm import tqdm

from model import GoogLeNet


def main():
    device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
    print("using {} device.".format(device))

    data_transform = {
        "train": transforms.Compose([transforms.RandomResizedCrop(224),
                                     transforms.RandomHorizontalFlip(),  # 随机左右翻转
                                     # transforms.RandomVerticalFlip(), # 随机上下翻转
                                     transforms.ColorJitter(brightness=0.5, contrast=0.5, saturation=0.5, hue=0.1),
                                     transforms.RandomRotation(degrees=5),
                                     transforms.ToTensor(),
                                     transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))]),
        "val": transforms.Compose([transforms.Resize((224, 224)),
                                   transforms.ToTensor(),
                                   transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])}

    train_dataset = datasets.ImageFolder(root='./Training',
                                         transform=data_transform["train"])
    train_num = len(train_dataset)
    flower_list = train_dataset.class_to_idx
    cla_dict = dict((val, key) for key, val in flower_list.items())
    json_str = json.dumps(cla_dict, indent=4)
    with open(
            'class_indices.json', 'w') as json_file:
        json_file.write(json_str)

    batch_size = 32
    nw = min([os.cpu_count(), batch_size if batch_size > 1 else 0, 8])  # number of workers
    print('Using {} dataloader workers every process'.format(nw))

    train_loader = torch.utils.data.DataLoader(train_dataset,
                                               batch_size=batch_size, shuffle=True,
                                               num_workers=nw)

    validate_dataset = datasets.ImageFolder(root='./Test',
                                            transform=data_transform["val"])
    val_num = len(validate_dataset)
    validate_loader = torch.utils.data.DataLoader(validate_dataset,
                                                  batch_size=batch_size, shuffle=False,
                                                  num_workers=nw)

    print("using {} images for training, {} images for validation.".format(train_num, val_num))

    # test_data_iter = iter(validate_loader)
    # test_image, test_label = test_data_iter.next()

    net = GoogLeNet(num_classes=131, aux_logits=True, init_weights=True)  # num_classes根据分类的数量而定
    # 如果要使用官方的预训练权重，注意是将权重载入官方的模型，不是我们自己实现的模型
    # 官方的模型中使用了bn层以及改了一些参数，不能混用
    # import torchvision
    # net = torchvision.models.googlenet(num_classes=5)
    # model_dict = net.state_dict()
    # # 预训练权重下载地址: https://download.pytorch.org/models/googlenet-1378be20.pth
    # pretrain_model = torch.load("googlenet.pth")
    # del_list = ["aux1.fc2.weight", "aux1.fc2.bias",
    #             "aux2.fc2.weight", "aux2.fc2.bias",
    #             "fc.weight", "fc.bias"]
    # pretrain_dict = {k: v for k, v in pretrain_model.items() if k not in del_list}
    # model_dict.update(pretrain_dict)
    # net.load_state_dict(model_dict)
    net.to(device)
    loss_function = nn.CrossEntropyLoss()
    optimizer = optim.Adam(net.parameters(), lr=0.0003)

    epochs = 30
    best_acc = 0.0
    save_path = './googleNet.pth'
    train_steps = len(train_loader)
    for epoch in range(epochs):
        # train
        net.train()
        running_loss = 0.0
        train_bar = tqdm(train_loader, file=sys.stdout)
        for step, data in enumerate(train_bar):
            images, labels = data
            optimizer.zero_grad()
            logits, aux_logits2, aux_logits1 = net(images.to(device))
            loss0 = loss_function(logits, labels.to(device))
            loss1 = loss_function(aux_logits1, labels.to(device))
            loss2 = loss_function(aux_logits2, labels.to(device))
            loss = loss0 + loss1 * 0.3 + loss2 * 0.3
            loss.backward()
            optimizer.step()

            # print statistics
            running_loss += loss.item()

            train_bar.desc = "train epoch[{}/{}] loss:{:.3f}".format(epoch + 1,
                                                                     epochs,
                                                                     loss)

        # validate
        net.eval()
        acc = 0.0  # accumulate accurate number / epoch
        with torch.no_grad():
            val_bar = tqdm(validate_loader, file=sys.stdout)
            for val_data in val_bar:
                val_images, val_labels = val_data
                outputs = net(val_images.to(device))  # eval model only have last output layer
                predict_y = torch.max(outputs, dim=1)[1]
                acc += torch.eq(predict_y, val_labels.to(device)).sum().item()

        val_accurate = acc / val_num
        print('[epoch %d] train_loss: %.3f  val_accuracy: %.3f' %
              (epoch + 1, running_loss / train_steps, val_accurate))

        if val_accurate > best_acc:
            best_acc = val_accurate
            torch.save(net.state_dict(), save_path)

    print('Finished Training')


if __name__ == '__main__':
    main()


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