VGGNet原理及tensorflow实现

VGGNet介绍：

VGGNet是牛津大学计算机视觉组和Google DeepMind一起研发的卷积神经网络，VGGNet探索了卷积神经网络的深度与其性能之间的关系。VGG的结构特点是通过反复堆叠3x3的卷积核和2x2的max-pool, 与在其之前的卷积神经网络相比，错误率大大降低。同时，VGGNet扩展性强，迁移其他数据上的泛化能力好，因此VGGNe常被用来提取图像特征。

VGG各级别网络结构：

从上面的结构图可以看到。VGG拥有5段卷积，每一段内又2-3个卷积层，同时每一段的尾部会连接一个最大池化层，用于缩小图片的尺寸。可以看到VGG中经常出现多个完全一样的3x3的卷积核堆叠到一起，这种卷积层串联是一种非常有用的设计。两个3x3的卷积层串联相当于一个5x5的卷积层，也就是说一个像素会和周围5个像素产生关联，即感受野的大小是5x5,：

个人理解的两个3x3的卷积层串联相当于一个5x5的卷积层：

以手写字体图片为例，假设输入图像的尺寸为28x28, 则经过两个3x3的卷积层后：（假设padding="VALID"， strides=1）

    1. （28-3+1）/1 = 26

    2.    (26-3+1) / 1 = 24

同样大小的图像，经过一个5x5的卷积层之后：

    1.   （28-5+1）/1 = 24

而且多个小的卷积层串联有如下优势：

1.参数更少， 假设3个3x3x3的卷积层串联，参数的数量3x3xN+3x3xN+3x3xN=3x3x3xN,而一个7x7的卷积层的参数为7x7xN;

前者只有后者参数的(3x3x3xN)/(7x7xN)=55%.

2. 多个卷积层串联比一个卷积层拥有更多的非线性变换（三次使用激活函数），使得网络能够更好地学习特征。

VGG-16:

VGG-16 feature-map的维度如下所示：

VGG在训练时做数据增强的方法：

将原始图像缩放到不同的尺寸，然后再随机裁剪成224x224大小的图像，增加数据量，防止模型过拟合。（这一点和AlexNet中的数据增强方法类似， AlexNet中对裁剪得到的图象还进行了左右反转）。

对于VGG,同时有如下结论：

(1) LRN层的作用不大

(2) 越深的网络效果越好。

(3) 大一些的卷积核可以学习到更多的空间特征

关于1x1的卷积核的作用：

（参考博客：https://blog.csdn.net/wonengguwozai/article/details/72980828

                      https://www.jianshu.com/p/04c2a9ccaa75）

1. 实现跨通道的交互和信息整合
2. 进行卷积核通道数的降维和升维

3. 增加网络的非线性
3.对于单通道feature map 用单核卷积即为乘以一个参数，而一般情况都是多核卷积多通道，实现多个feature map的线性组合

VGG16的tensorflow代码：

数据用的是博客车型分类中的数据集：

（在车型分类中，已经对数据的处理和读取做了详细的介绍，代码正确，但是本人无法运行模型，只有笔记本囧）

import tensorflow as tf
import math
import time
import os
from tqdm import tqdm
from PIL import Image, ImageDraw, ImageFont
import numpy as np
 
 
class Data:
    """
    读取训练集，验证集，测试集数据
    """
    def __init__(self, batch_size, data_path, val_data, test_data):
        """
        :param batch_size:
        :param data_path:  训练数据路径
        :param val_data:   验证集路径
        :param test_data:  测试集路径
        """
        self.batch_size = batch_size
        self.data_path = data_path
        self.labels_name = []
        self.val_data = val_data
        self.test_data = test_data
        # self.images = []
        self.image_names = os.listdir(self.data_path)  # 所有的图片集合
        for name in tqdm(self.image_names):
            # image_path = os.path.join(self.data_path, name)
            # image = Image.open(image_path)
            # image = np.array(image) / 255.0   # 图像像素值归一化到0-1
            """
            归一化的原因
            1. 转换成标准模式，防止仿射变换的影响。
            2、减小几何变换的影响。
            3、加快梯度下降求最优解的速度。
            """
            # self.images.append(image)
            class_name = name.split('.')[0].split('_')[-1]
            self.labels_name.append(class_name)
        class_set = set(self.labels_name)
        self.labels_dict = {}
        for v, k in enumerate(class_set):
            self.labels_dict[k] = v
        print("Data Loading finished!")
        print("Label dict: ", self.labels_dict)
        self.labels = [self.labels_dict.get(k) for k in self.labels_name]  # 将标签名转化为标签的编号
        print("Label names: ", self.labels_name)
        print("Labels is: ", self.labels)
 
    def get_batch(self, count):
        """
         get_batch函数按照batch将图片读入，因为一次读入全部图片会导致内存暴增
        :param count:
        :return:
        """
        start = count * self.batch_size
        end = (count + 1) * self.batch_size
        start_pos = max(0, start)
        end_pos = min(end, len(self.labels))
        images_name_batch = self.image_names[start_pos: end_pos]
        images = []  # 存放图片
        for images_name in images_name_batch:
            image_path = os.path.join(self.data_path, images_name)
            image = Image.open(image_path)
            image = np.array(image) / 255.0  # 图像像素值归一化到0-1
            images.append(image)
        labels = self.labels[start_pos: end_pos]
        datas = np.array(images)
        labels = np.array(labels)
        return datas, labels
 
    def get_batch_num(self):
        return len(self.labels) // self.batch_size
 
    def get_batch_size(self):
        return self.batch_size
 
    def get_val_data(self):
        val_names = os.listdir(self.val_data)  # 验证集图片
        val_images = []
        val_labels = []
        for name in val_names:
            image_path = os.path.join(self.val_data, name)
            image = Image.open(image_path)
            image = np.array(image) / 255.0  # 图像像素值归一化到0-1
            """
            归一化的原因
            1. 转换成标准模式，防止仿射变换的影响。
            2、减小几何变换的影响。
            3、加快梯度下降求最优解的速度。
            """
            val_images.append(image)
            class_name_val = name.split('.')[0].split('_')[-1]
            val_labels.append(class_name_val)
        val_images = np.array(val_images)
        val_labels = [self.labels_dict.get(k) for k in val_labels]  # 将标签名转化为标签的编号
        val_labels = np.array(val_labels)
        return val_images, val_labels
 
    def get_label_dict(self):
        return self.labels_dict
 
    def get_test_info(self):
        """
        测试数据没有标签
        :return:
        """
        test_names = os.listdir(self.test_data)
        return self.test_data, test_names
 
 
class Model:
    def __init__(self, input_size, learning_rate, keep_prob, class_num, lamb=0.01):
        self.input_size = input_size
        self.learning_rate = learning_rate
        self.keep_prob = keep_prob
        self.loss = 0
        self.train_op = 0
        self.losses = 0
        self.lamb = lamb
        self.class_num = class_num
 
    def conv_op(self, input_tensor, name, kernel, stride, padding, train_flag):
        """
        # 定义创建卷积层的函数
        :param input_tensor:  输入的张量 [w, h, d]
        :param name:          卷积层名称
        :param kernel:        卷积核的尺度 [宽度， 高度， 深度]
        :param stride:        卷积核移动的步长[w, h]
        :param padding:        "SAME", "VALID"
        :return:
        """
        depth = input_tensor.get_shape()[-1].value  # 获取输入张量的深度
        with tf.name_scope(name):
            filter = tf.get_variable(name=name + '_weight', shape=[kernel[0], kernel[1], depth, kernel[2]], dtype=tf.float32,
                                     initializer=tf.contrib.layers.xavier_initializer_conv2d())
            # xavier_initializer会根据某一层网络的输入输出的节点数，自动调整最合适的分布
            # xavier指出， 如果深度学习模型的权重初始化的太小，那么信号将在每层间传递时逐渐缩小而难以产生作用，
            # 权重太大将导致信号在每层之间传递时逐渐放大并导致发散和失效
            # xavier_initializer让权重满足均值为0， 方差为2/（n_in, n_out），分布可以用均匀分布或者高斯分布
            if train_flag:
                tf.add_to_collection('loss', tf.contrib.layers.l2_regularizer(self.lamb)(filter))   # 正则化
            conv = tf.nn.conv2d(input=input_tensor, filter=filter, strides=[1, stride[0], stride[1], 1],
                                padding=padding)
            biases = tf.get_variable(name=name + 'bias', shape=[kernel[2]], dtype=tf.float32,
                                     initializer=tf.constant_initializer(0.0))
            layer = tf.nn.relu(tf.nn.bias_add(value=conv, bias=biases), name=name + 'layer')
            return layer
 
    def fc_op(self, input_tensor, name, output_nodes, train_flag):
        """
        全连接层
        :param input_tensor:  输入的张量
        :param name:          名称
        :param output_nodes:   输出节点的个数
        :return:
        """
        length = input_tensor.get_shape()[-1].value
        with tf.name_scope(name):
            weight = tf.get_variable(name=name + '_weight', shape=[length, output_nodes], dtype=tf.float32,
                                     initializer=tf.contrib.layers.xavier_initializer())
            biases = tf.get_variable(name=name + '_bias', shape=[output_nodes], dtype=tf.float32,
                                     initializer=tf.constant_initializer(0.1))
            out_put = tf.nn.bias_add(value=tf.matmul(input_tensor, weight), bias=biases)
            layer = tf.nn.relu(out_put)
            if train_flag:
                tf.add_to_collection("loss", tf.contrib.layers.l2_regularizer(self.lamb)(weight))  # L2正则化
                layer = tf.nn.dropout(layer, keep_prob=self.keep_prob)
            return layer
 
    def maxpool_op(self, input_tensor, name, kernel, stride, padding):
        """
        :param input_tensor:    输入张量
        :param name:            名称
        :param kernel:          核  [w, h]
        :param stride:          步长  [w, h]
        :param padding:         “SAME"  VALID
        :return:
        """
        with tf.name_scope(name):
            layer = tf.nn.max_pool(value=input_tensor, ksize=[1, kernel[0], kernel[1], 1],
                                   strides=[1, stride[0], stride[1], 1], padding=padding, name=name + '_layer')
            return layer
 
    def inference(self, x, train_flag):
        """
        :param x: 输入张量
        :param train_flag:
        :return:
        """
        # VGG的第一段是两个3x3的卷积层串联，再接一个池化层，卷积层的深度为64
        conv1_1 = self.conv_op(input_tensor=x, name="conv1_1", kernel=[3, 3, 64], stride=[1, 1], padding="SAME",
                               train_flag=train_flag)
        conv1_2 = self.conv_op(input_tensor=conv1_1, name="conv1_2", kernel=[3, 3, 64], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        pool1 = self.maxpool_op(input_tensor=conv1_2, name="pool_1", kernel=[2, 2], stride=[2, 2], padding='SAME')  # 100
 
        # VGG的第2段是两个3x3的卷积层串联，再接一个池化层，但是卷层的深度变成128
        conv2_1 = self.conv_op(input_tensor=pool1, name="conv2_1", kernel=[3, 3, 128], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        conv2_2 = self.conv_op(input_tensor=conv2_1, name="conv2_2", kernel=[3, 3, 128], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        pool2 = self.maxpool_op(input_tensor=conv2_2, name="pool_2", kernel=[2, 2], stride=[2, 2], padding="SAME")  # 50
 
        # VGG的第3段是三个3x3的卷积层串联，再接一个池化层，但是卷层的深度变成256
        conv3_1 = self.conv_op(input_tensor=pool2, name="conv3_1", kernel=[3, 3, 256], stride=[1, 1], padding="SAME",
                               train_flag=train_flag)
        conv3_2 = self.conv_op(input_tensor=conv3_1, name="conv3_2", kernel=[3, 3, 256], stride=[1, 1], padding="SAME",
                               train_flag=train_flag)
        conv3_3 = self.conv_op(input_tensor=conv3_2, name="conv3_3", kernel=[3, 3, 256], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        pool3 = self.maxpool_op(input_tensor=conv3_3, name="pool_3", kernel=[2, 2], stride=[2, 2], padding='SAME')  # 25
 
        # VGG的第四段，三个3x3的卷积层串联，再加一个最大池化层，卷积层通道数512 进一步加深网络的深度，减小图像的尺寸
        conv4_1 = self.conv_op(input_tensor=pool3, name="conv4_1", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        conv4_2 = self.conv_op(input_tensor=conv4_1, name="conv4_2", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        conv4_3 = self.conv_op(input_tensor=conv4_2, name="conv4_3", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        pool4 = self.maxpool_op(input_tensor=conv4_3, name="pool_4", kernel=[2,2], stride=[2, 2], padding='SAME')  # 13
 
        # VGG的第五段，三个3x3的卷积层串联，再加一个最大池化层，卷积层通道数512，步长1，池化层进一步缩小图像的尺寸
        conv5_1 = self.conv_op(input_tensor=pool4, name="conv5_1", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        conv5_2 = self.conv_op(input_tensor=conv5_1, name="conv5_2", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        conv5_3 = self.conv_op(input_tensor=conv5_2, name="conv5_3", kernel=[3, 3, 512], stride=[1, 1], padding='SAME',
                               train_flag=train_flag)
        pool5 = self.maxpool_op(input_tensor=conv5_3, name="pool_5", kernel=[2, 2], stride=[2, 2], padding='SAME')  # 7
 
        # 全连接层
        pool5_shape = pool5.get_shape()
        nodes = pool5_shape[1].value * pool5_shape[2].value * pool5_shape[3].value    # 计算节点数
        pool5_flatten = tf.reshape(pool5, shape=[-1, nodes], name="pool5_flatten")
 
        fc1 = self.fc_op(input_tensor=pool5_flatten, name="fc1", output_nodes=4096, train_flag=train_flag)
        fc2 = self.fc_op(input_tensor=fc1, name='fc2', output_nodes=2048, train_flag=train_flag)    # 输出
        fc3 = self.fc_op(input_tensor=fc2, name='fc3', output_nodes=self.class_num, train_flag=train_flag)
        return fc3    # 网络输出
 
    def train(self, data, train_step):
        with tf.name_scope("placeholder"):
            x = tf.placeholder(dtype=tf.float32, shape=[None, self.input_size[0], self.input_size[1],
                                                        self.input_size[2]],
                               name='x_input')
            y_ = tf.placeholder(dtype=tf.int32, shape=[None], name='y_input')
        inference_output = self.inference(x, train_flag=True)
        self.loss = tf.reduce_mean(tf.nn.sparse_softmax_cross_entropy_with_logits(logits=inference_output, labels=y_,
                                                                                  name='loss'))
        tf.add_to_collection('loss', self.loss)
        self.losses = tf.add_n(tf.get_collection('loss'))
        self.train_op = tf.train.AdamOptimizer(learning_rate=self.learning_rate).minimize(self.losses)
        with tf.Session() as sess:
            init_op = tf.group(tf.local_variables_initializer(), tf.global_variables_initializer())
            sess.run(init_op)
            for step in range(train_step):
                batch_num = data.get_batch_num()
                total_loss = 0.0
                for batch_count in tqdm(range(batch_num)):
                    train_x, train_y = data.get_batch(batch_count)
                    feed_dict = {x: train_x, y_: train_y}
                    _, loss = sess.run([self.train_op, self.losses], feed_dict=feed_dict)
                    total_loss += loss
                print("After {} step training the loss is {}".format(step, total_loss/batch_num))
 
 
if __name__ == "__main__":
    data_path = r"E:\back_up\NLP\course\rename_train_dr"     # 训练集
    val_data = r"E:\back_up\NLP\course\rename_val_dr"        # 验证集
    test_data = r"E:\back_up\NLP\course\rename_test"         # 测试集
    # model = r"E:\back_up\code\112\tensorflow_project\newbook\chapter6\model\model"
    # board = r"E:\back_up\code\112\tensorflow_project\newbook\chapter6\board_data"
    # test_result = r"E:\back_up\NLP\course\test_result"
    data = Data(batch_size=2, data_path=data_path, val_data=val_data, test_data=test_data)
    model = Model(input_size=[200, 200, 3], learning_rate=0.001, keep_prob=0.6, class_num=10)
    model.train(data=data, train_step=5)