搭建一个densenet网络

A：搭建一个densenet网络的步骤如下：

1.导入必要的库和模块

import tensorflow as tf
from tensorflow.keras.layers import Input, Conv2D, BatchNormalization, Activation, Concatenate, AveragePooling2D, Dense, Flatten
from tensorflow.keras.models import Model

2.定义密集块（DenseBlock）函数

def dense_block(x, n_filters, n_layers):
    for i in range(n_layers):
        # 每层使用BN、ReLU和2D卷积层
        x_bn = BatchNormalization()(x)
        x_relu = Activation('relu')(x_bn)
        x_conv = Conv2D(n_filters, kernel_size=(3,3), padding='same')(x_relu)
        # 连接当前层和之前所有层的输出
        x = Concatenate()([x, x_conv])
    return x

3.定义过渡层（TransitionLayer）函数

def transition_layer(x, n_filters):
    # 使用BN和ReLU
    x = BatchNormalization()(x)
    x = Activation('relu')(x)
    # 使用1x1的卷积层压缩通道数
    x = Conv2D(n_filters, kernel_size=(1,1), padding='same')(x)
    # 使用平均池化层压缩空间大小
    x = AveragePooling2D(pool_size=(2,2))(x)
    return x

4.组合密集块和过渡层构建DenseNet网络结构

def DenseNet(input_shape=(32,32,3), n_classes=10, growth_rate=12, n_dense_blocks=3, n_layers_per_block=4):
    # 定义输入层
    inputs = Input(shape=input_shape)
    # 使用一个普通的卷积层进行特征提取
    x = Conv2D(64, kernel_size=(3,3), padding='same', activation='relu')(inputs)
    # 构建多个密集块和过渡层
    for i in range(n_dense_blocks):
        x = dense_block(x, n_filters=growth_rate, n_layers=n_layers_per_block)
        # 最后一个密集块后不需要过渡层
        if i != n_dense_blocks - 1:
            x = transition_layer(x, n_filters=x.shape[-1] // 2)
    # 压平输出并添加全连接层
    x = Flatten()(x)
    x = Dense(256, activation='relu')(x)
    # 输出层使用softmax函数激活
    outputs = Dense(n_classes, activation='softmax')(x)
    # 定义模型并返回
    model = Model(inputs=inputs, outputs=outputs)
    return model

可以使用如下代码进行测试：

model = DenseNet()
model.summary()

输出结果：

Model: "model_1"
__________________________________________________________________________________________________
Layer (type)                    Output Shape         Param #     Connected to                     
==================================================================================================
input_2 (InputLayer)            [(None, 32, 32, 3)]  0                                            
__________________________________________________________________________________________________
conv2d_44 (Conv2D)              (None, 32, 32, 64)   1792        input_2[0][0]                    
__________________________________________________________________________________________________
batch_normalization_44 (BatchNo (None, 32, 32, 64)   256         conv2d_44[0][0]                  
__________________________________________________________________________________________________
activation_44 (Activation)      (None, 32, 32, 64)   0           batch_normalization_44[0][0]     
__________________________________________________________________________________________________
conv2d_45 (Conv2D)              (None, 32, 32, 12)   6924        activation_44[0][0]              
__________________________________________________________________________________________________
concatenate_40 (Concatenate)    (None, 32, 32, 76)   0           conv2d_44[0][0]                  
                                                                 conv2d_45[0][0]                  
__________________________________________________________________________________________________
batch_normalization_45 (BatchNo (None, 32, 32, 76)   304         concatenate_40[0][0]             
__________________________________________________________________________________________________
activation_45 (Activation)      (None, 32, 32, 76)   0           batch_normalization_45[0][0]     
__________________________________________________________________________________________________
conv2d_46 (Conv2D)              (None, 32, 32, 12)   7812        activation_45[0][0]              
__________________________________________________________________________________________________
concatenate_41 (Concatenate)    (None, 32, 32, 88)   0           concatenate_40[0][0]             
                                                                 conv2d_46[0][0]                  
__________________________________________________________________________________________________
batch_normalization_46 (BatchNo (None, 32, 32, 88)   352         concatenate_41[0][0]             
__________________________________________________________________________________________________
activation_46 (Activation)      (None, 32, 32, 88)   0           batch_normalization_46[0][0]     
__________________________________________________________________________________________________
conv2d_47 (Conv2D)              (None, 32, 32, 12)   9528        activation_46[0][0]              
__________________________________________________________________________________________________
concatenate_42 (Concatenate)    (None, 32, 32, 100)  0           concatenate_41[0][0]             
                                                                 conv2d_47[0][0]                  
__________________________________________________________________________________________________
batch_normalization_47 (BatchNo (None, 32, 32, 100)  400         concatenate_42[0][0]             
__________________________________________________________________________________________________
...
conv2d_84 (Conv2D)              (None, 4, 4, 12)     21468       activation_83[0][0]              
__________________________________________________________________________________________________
concatenate_76 (Concatenate)    (None, 4, 4, 232)    0           concatenate_75[0][0]             
                                                                 conv2d_84[0][0]                  
__________________________________________________________________________________________________
batch_normalization_84 (BatchNo (None, 4, 4, 232)    928         concatenate_76[0][0]             
__________________________________________________________________________________________________
activation_84 (Activation)      (None, 4, 4, 232)    0           batch_normalization_84[0][0]     
__________________________________________________________________________________________________
conv2d_85 (Conv2D)              (None, 4, 4, 12)     25164       activation_84[0][0]              
__________________________________________________________________________________________________
concatenate_77 (Concatenate)    (None, 4, 4, 244)    0           concatenate_76[0][0]             
                                                                 conv2d_85[0][0]                  
__________________________________________________________________________________________________
batch_normalization_85 (BatchNo (None, 4, 4, 244)    976         concatenate_77[0][0]             
__________________________________________________________________________________________________
activation_85 (Activation)      (None, 4, 4, 244)    0           batch_normalization_85[0][0]     
__________________________________________________________________________________________________
conv2d_86 (Conv2D)              (None, 4, 4, 12)     26388       activation_85[0][0]              
__________________________________________________________________________________________________
concatenate_78 (Concatenate)    (None, 4, 4, 256)    0           concatenate_77[0][0]             
                                                                 conv2d_86[0][0]                  
__________________________________________________________________________________________________
flatten_1 (Flatten)             (None, 4096)         0           concatenate_78[0][0]             
__________________________________________________________________________________________________
dense_2 (Dense)                 (None, 256)          1048832     flatten_1[0][0]                  
__________________________________________________________________________________________________
dense_3 (Dense)                 (None, 10)           2570        dense_2[0][0]                    
==================================================================================================
Total params: 1,275,738
Trainable params: 1,270,074
Non-trainable params: 5,664
__________________________________________________________________________________________________