图像分类——ResNet

残差块

左图残差块实现如下

import tensorflow as tf
from tensorflow.keras import layers,activations

#残差块
class Residul(tf.keras.Model):
    def __init__(self,num_channels,use_1x1conv=False,strides=1):
        super(Residul,self).__init__() #调用基类init方法
        self.conv1=layers.Conv2D(num_channels,kernel_size=3,padding='same',strides=strides)
        self.conv2=layers.Conv2D(num_channels,kernel_size=3,strides=strides)
        if use_1x1conv:
            self.conv3=layers.Conv2D(num_channels,kernel_size=1,strides=strides)
        else:
            self.conv3=None
        self.bn1=layers.BatchNormalization()
        self.bn2=layers.BatchNormalization()
            
    def call(self,x):
        y=activations.relu(self.bn1(self.conv1(x)))
        y=self.bn2(self.conv2(y))
        if self.conv3:
            x=self.conv3(x)
        outputs=activations.relu(y+x)
        return outputs

ResNet模型

#残差模块
class ResnetBlock(tf.keras.layers.Layer):
    def __init__(self,num_channels,num_res,first_block=False):
        super(ResnetBlock,self).__init__()
        #存储残差块
        self.listLayers=[]
        #遍历残差数目生成模块
        for i in range(num_res):
            #如果是第一个残差块而且不是第一个模块时
            if i ==0 and not first_block:
                self.listLayers.append(Residul(num_channels,use_1x1conv=True,strides=2))
            else:
                self.listLayers.append(Residul(num_channels))
        
    def call(self,x):
        for layers in self.listLayers:
            x=layers(x)
        return x

#构建resNet网络
class ResNet(tf.keras.Model):
    def __init__(self,num_blocks):
        super(ResNet,self).__init__()
        self.conv=layers.Conv2D(64,kernel_size=7,strides=2,padding='same')
        self.bn=layers.BatchNormalization()
        self.relu=layers.Activation('relu')
        self.mp=layers.MaxPool2D(pool_size=3,strides=2,padding='same')
        #残差模块
        self.res_block1=ResnetBlock(64,num_blocks[0],first_block=True)
        self.res_block2=ResnetBlock(128,num_blocks[1])
        self.res_block3=ResnetBlock(256,num_blocks[2])
        self.res_block4=ResnetBlock(512,num_blocks[3])
        #GAP
        self.gap=layers.GlobalAveragePooling2D() #全局平均池化
        #全连接层
        self.fc=layers.Dense(units=10,activation=tf.keras.activations.softmax)
    
    def call(self,x):
        #输入部分的传输过程
        x=self.conv(x)
        x=self.bn(x)
        x=self.relu(x)
        x=self.mp(x)
        #block
        x=self.res_block1(x)
        x=self.res_block2(x)
        x=self.res_block3(x)
        x=self.res_block4(x)
        #输出部分的传输
        x=self.gap(x)
        x=self.fc(x)
        return x

mynet=ResNet([2,2,2,2])
X=tf.random.uniform((1,224,224,1))
y=mynet(X)
mynet.summary()

手写数字识别

和Alex Net一样