TensorFlow2學習十七、實作ResNet（二）封裝ResNet

一、 ResRet18網絡結構

下面測試代碼使用ResNet18訓練CIFAR10。

• 測試環境 google colab
• TF2.0

二、模型類

1. 指定TF2.0

try:
  # %tensorflow_version only exists in Colab.
  %tensorflow_version 2.x
except Exception:
  pass      

2. 模型類

class BasicBlock(layers.Layer):
    def __init__(self,filter_num,stride=1):
        super(BasicBlock, self).__init__()
        self.conv1=layers.Conv2D(filter_num,(3,3),strides=stride,padding='same')
        self.bn1=layers.BatchNormalization()
        self.relu=layers.Activation('relu')

        self.conv2=layers.Conv2D(filter_num,(3,3),strides=1,padding='same')
        self.bn2 = layers.BatchNormalization()

        if stride!=1:
            self.downsample=Sequential()
            self.downsample.add(layers.Conv2D(filter_num,(1,1),strides=stride))
        else:
            self.downsample=lambda x:x
    def call(self,input,training=None):
        out=self.conv1(input)
        out=self.bn1(out)
        out=self.relu(out)

        out=self.conv2(out)
        out=self.bn2(out)

        identity=self.downsample(input)
        output=layers.add([out,identity])
        output=tf.nn.relu(output)
        return output

class ResNet(keras.Model):
    def __init__(self,layer_dims,num_classes=10):
        super(ResNet, self).__init__()
        # 預處理層
        self.stem=Sequential([
            layers.Conv2D(64,(3,3),strides=(1,1)),
            layers.BatchNormalization(),
            layers.Activation('relu'),
            layers.MaxPool2D(pool_size=(2,2),strides=(1,1),padding='same')
        ])
        # resblock
        self.layer1=self.build_resblock(64,layer_dims[0])
        self.layer2 = self.build_resblock(128, layer_dims[1],stride=2)
        self.layer3 = self.build_resblock(256, layer_dims[2], stride=2)
        self.layer4 = self.build_resblock(512, layer_dims[3], stride=2)

        # there are [b,512,h,w]
        # 自适應
        self.avgpool=layers.GlobalAveragePooling2D()
        self.fc=layers.Dense(num_classes)



    def call(self,input,training=None):
        x=self.stem(input)
        x=self.layer1(x)
        x=self.layer2(x)
        x=self.layer3(x)
        x=self.layer4(x)
        # [b,c]
        x=self.avgpool(x)
        x=self.fc(x)
        return x
        
    def build_resblock(self,filter_num,blocks,stride=1):
        res_blocks= Sequential()
        # may down sample
        res_blocks.add(BasicBlock(filter_num,stride))
        # just down sample one time
        for pre in range(1,blocks):
            res_blocks.add(BasicBlock(filter_num,stride=1))
        return res_blocks
def ResNet18():
    return  ResNet([2,2,2,2])

def ResNet34():
    return ResNet(BasicBlock, [3,4,6,3])

def ResNet50():
    return ResNet(Bottleneck, [3,4,6,3])

def ResNet101():
    return ResNet(Bottleneck, [3,4,23,3])

def ResNet152():
    return ResNet(Bottleneck, [3,8,36,3])      

三、 使用resnet18模型訓練CIFAR10

import os
import tensorflow as tf
# 我在colab運作注釋掉了這一句，模型儲存成單個檔案時這句應當保留
#from Resnet import ResNet18
from tensorflow.keras import datasets,layers,optimizers,Sequential,metrics

os.environ["TF_CPP_MIN_LOG_LEVEL"]='2'
tf.random.set_seed(2345)


def preprocess(x,y):
    x=2*tf.cast(x,dtype=tf.float32)/255.-1
    y=tf.cast(y,dtype=tf.int32)
    return x,y
(x_train,y_train),(x_test,y_test)=datasets.cifar10.load_data()
y_train=tf.squeeze(y_train,axis=1)
y_test=tf.squeeze(y_test,axis=1)
# print(x_train.shape,y_train.shape,x_test.shape,y_test.shape)
train_data=tf.data.Dataset.from_tensor_slices((x_train,y_train))
train_data=train_data.shuffle(1000).map(preprocess).batch(64)

test_data=tf.data.Dataset.from_tensor_slices((x_test,y_test))
test_data=test_data.map(preprocess).batch(64)

sample=next(iter(train_data))
print('sample:',sample[0].shape,sample[1].shape,
      tf.reduce_min(sample[0]),tf.reduce_max(sample[0]))

def main():
    model=ResNet18()
    model.build(input_shape=(None,32,32,3))
    model.summary()
    optimizer=optimizers.Adam(lr=1e-3)
    for epoch in range(50):
        for step,(x,y) in enumerate(train_data):
            with tf.GradientTape() as tape:
                logits=model(x)
                y_onehot=tf.one_hot(y,depth=10)
                loss=tf.losses.categorical_crossentropy(y_onehot,logits,from_logits=True)
                loss=tf.reduce_mean(loss)
            grads=tape.gradient(loss,model.trainable_variables)
            optimizer.apply_gradients(zip(grads,model.trainable_variables))
            if step%100==0:
                print(epoch,step,'loss',float(loss))
        total_num=0
        total_correct=0
        for x,y in test_data:
            logits=model(x)
            prob=tf.nn.softmax(logits,axis=1)
            pred=tf.argmax(prob,axis=1)
            pred=tf.cast(pred,dtype=tf.int32)
            correct=tf.cast(tf.equal(pred,y),dtype=tf.int32)
            correct=tf.reduce_sum(correct)
            total_num+=x.shape[0]
            total_correct+=int(correct)
        acc=total_correct/total_num
        print(epoch,'acc:',acc)
if __name__ == '__main__':
    main()