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深度学习本质上是表示学习，它通过多层非线性神经网络模型从底层特征中学习出对具体任务而言更有效的高级抽象特征。针对一个具体的任务，我们往往会遇到这种情况：需要用一个模型学习出特征表示，然后将学习出的特征表示作为另一个模型的输入。这就要求我们会获取模型中间层的输出，下面以具体代码形式介绍两种具体方法。
目录
1 通过K.function()函数打印模型中间层的输出
2 通过函数API打印模型中间层的输出
这里的任务是使用多层全连接神经网络预测Mnist图像数据集的标签，模型相对简单，结构图如下：
可以看到模型是一个三层的全连接神经网络。针对该任务的代码及训练效果如下：
#--coding:utf-8-- """ @author:taoshouzheng @time:2019/4/10 19:24 @email:tsz1216@sina.com """
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import numpy as np from keras.datasets import mnist from keras.models import Sequential from keras.layers.core import Dense, Activation from keras.optimizers import SGD from keras.utils import np_utils
np.random.seed(1)
NB_EPOCH = 20
BATCH_SIZE = 128
VERBOSE = 1
NB_CLASSES = 10
OPTIMIZER = SGD()
VALIDATION_SPLIT = 0.2
(X_train, Y_train), (X_test, Y_test) = mnist.load_data() # X_train是60000行2828的数据，变形为60000784 RESHAPE = 784 X_train = X_train.reshape(60000, RESHAPE) # 变换形状 X_test = X_test.reshape(10000, RESHAPE) X_train = X_train.astype('float32') # 转换类型 X_test = X_test.astype('float32') X_train /= 255 # 归一化 X_test /= 255
print(X_train.shape[0], 'train samples') print(X_test.shape[0], 'test samples')
Y_train = np_utils.to_categorical(Y_train, NB_CLASSES) Y_test = np_utils.to_categorical(Y_test, NB_CLASSES)
model = Sequential() # 创建序贯模型实例 model.add(Dense(units=128, input_shape=(RESHAPE, ))) # 输入为784维数组 model.add(Activation('relu')) model.add(Dense(units=64)) model.add(Activation('relu')) model.add(Dense(units=NB_CLASSES)) model.add(Activation('softmax'))
model.summary()
model.compile(loss='categorical_crossentropy', optimizer=OPTIMIZER, metrics=['accuracy'])
history = model.fit(X_train, Y_train, batch_size=BATCH_SIZE, epochs=NB_EPOCH, verbose=VERBOSE, validation_split=VALIDATION_SPLIT)
score = model.evaluate(X_test, Y_test, verbose=VERBOSE) print('Test score:', score[0]) print('Test accuracy:', score[1]) 模型的训练效果如下：
以最后一代为例： Epoch 20/20
128/48000 [..............................] - ETA: 3s - loss: 0.2236 - acc: 0.9453 4352/48000 [=>............................] - ETA: 0s - loss: 0.1976 - acc: 0.9426 8192/48000 [====>.........................] - ETA: 0s - loss: 0.1939 - acc: 0.9454 12800/48000 [=======>......................] - ETA: 0s - loss: 0.1935 - acc: 0.9449 16512/48000 [=========>....................] - ETA: 0s - loss: 0.1919 - acc: 0.9450 20864/48000 [============>.................] - ETA: 0s - loss: 0.1952 - acc: 0.9446 24704/48000 [==============>...............] - ETA: 0s - loss: 0.1947 - acc: 0.9447 28672/48000 [================>.............] - ETA: 0s - loss: 0.1933 - acc: 0.9449 32384/48000 [===================>..........] - ETA: 0s - loss: 0.1932 - acc: 0.9450 35968/48000 [=====================>........] - ETA: 0s - loss: 0.1919 - acc: 0.9456 39808/48000 [=======================>......] - ETA: 0s - loss: 0.1930 - acc: 0.9455 43904/48000 [==========================>...] - ETA: 0s - loss: 0.1921 - acc: 0.9457 47232/48000 [============================>.] - ETA: 0s - loss: 0.1927 - acc: 0.9456 48000/48000 [==============================] - 1s 15us/step - loss: 0.1928 - acc: 0.9455 - val_loss: 0.1900 - val_acc: 0.9473
32/10000 [..............................] - ETA: 0s 2976/10000 [=======>......................] - ETA: 0s 6432/10000 [==================>...........] - ETA: 0s 10000/10000 [==============================] - 0s 15us/step Test score: 0.1925726256787777 Test accuracy: 0.9442 现在我们要获取第三个全连接层dense_3的输出，有以下两种常用的方式：
1 通过K.function()函数打印模型中间层的输出 思路是通过K.function()函数创建Keras函数，然后再将数据输入到函数中即可。
representation_layer = K.function(inputs=[model.layers[0].input], outputs=[model.get_layer('dense_3').output])
representation = representation_layer([X_train]) 完整代码及运行效果如下：
#--coding:utf-8-- """ @author:taoshouzheng @time:2019/4/10 19:24 @email:tsz1216@sina.com """
import numpy as np from keras.datasets import mnist from keras.models import Sequential from keras.layers.core import Dense, Activation from keras.optimizers import SGD from keras.utils import np_utils from keras import backend as K
np.random.seed(1)
NB_EPOCH = 20
BATCH_SIZE = 128
VERBOSE = 1
NB_CLASSES = 10
OPTIMIZER = SGD()
VALIDATION_SPLIT = 0.2
(X_train, Y_train), (X_test, Y_test) = mnist.load_data() # X_train是60000行2828的数据，变形为60000784 RESHAPE = 784 X_train = X_train.reshape(60000, RESHAPE) # 变换形状 X_test = X_test.reshape(10000, RESHAPE) X_train = X_train.astype('float32') # 转换类型 X_test = X_test.astype('float32') X_train /= 255 # 归一化 X_test /= 255
print(X_train.shape[0], 'train samples') print(X_test.shape[0], 'test samples')
Y_train = np_utils.to_categorical(Y_train, NB_CLASSES) Y_test = np_utils.to_categorical(Y_test, NB_CLASSES)
model = Sequential() # 创建序贯模型实例 model.add(Dense(units=128, input_shape=(RESHAPE, ))) # 输入为784维数组 model.add(Activation('relu')) model.add(Dense(units=64)) model.add(Activation('relu')) model.add(Dense(units=NB_CLASSES)) model.add(Activation('softmax'))
model.summary()
model.compile(loss='categorical_crossentropy', optimizer=OPTIMIZER, metrics=['accuracy'])
history = model.fit(X_train, Y_train, batch_size=BATCH_SIZE, epochs=NB_EPOCH, verbose=VERBOSE, validation_split=VALIDATION_SPLIT)
score = model.evaluate(X_test, Y_test, verbose=VERBOSE) print('Test score:', score[0]) print('Test accuracy:', score[1])
representation_layer = K.function(inputs=[model.layers[0].input], outputs=[model.get_layer('dense_3').output])
representation = representation_layer([X_train])
representation = np.array(representation)[0]
print(representation.shape) print(type(representation)) print(representation)
2 通过函数API打印模型中间层的输出 与K.function()函数类似，根据输入输出关系通过Model()构建一个新的模型，然后在新的模型上对输入数据做预测。
representation_model = Model(inputs=model.inputs, outputs=model.get_layer('dense_3').output)
dense_3_output = representation_model.predict(X_train) 完整代码及运行效果如下：
#--coding:utf-8-- """ @author:taoshouzheng @time:2019/4/10 19:25 @email:tsz1216@sina.com """
#--coding:utf-8-- """ @author:taoshouzheng @time:2019/4/10 19:24 @email:tsz1216@sina.com """
import numpy as np from keras.datasets import mnist from keras.models import Sequential, Model from keras.layers.core import Dense, Activation from keras.optimizers import SGD from keras.utils import np_utils
np.random.seed(1)
NB_EPOCH = 20
BATCH_SIZE = 128
VERBOSE = 1
NB_CLASSES = 10
OPTIMIZER = SGD()
VALIDATION_SPLIT = 0.2
(X_train, Y_train_1), (X_test, Y_test) = mnist.load_data() # X_train是60000行2828的数据，变形为60000784 RESHAPE = 784 X_train = X_train.reshape(60000, RESHAPE) # 变换形状 X_test = X_test.reshape(10000, RESHAPE) X_train = X_train.astype('float32') # 转换类型 X_test = X_test.astype('float32') X_train /= 255 # 归一化 X_test /= 255
print(X_train.shape[0], 'train samples') print(X_test.shape[0], 'test samples')
Y_train = np_utils.to_categorical(Y_train_1, NB_CLASSES) Y_test = np_utils.to_categorical(Y_test, NB_CLASSES)
model = Sequential() # 创建序贯模型实例 model.add(Dense(units=128, input_shape=(RESHAPE, ))) # 输入为784维数组 model.add(Activation('relu')) model.add(Dense(units=64)) model.add(Activation('relu')) model.add(Dense(units=NB_CLASSES)) model.add(Activation('softmax'))
model.summary()
model.compile(loss='categorical_crossentropy', optimizer=OPTIMIZER, metrics=['accuracy'])
history = model.fit(X_train, Y_train, batch_size=BATCH_SIZE, epochs=NB_EPOCH, verbose=VERBOSE, validation_split=VALIDATION_SPLIT)
score = model.evaluate(X_test, Y_test, verbose=VERBOSE) print('Test score:', score[0]) print('Test accuracy:', score[1])
representation_model = Model(inputs=model.inputs, outputs=model.get_layer('dense_3').output)
dense_3_output = representation_model.predict(X_train)
print(dense_3_output.shape) print(type(dense_3_output)) print(dense_3_output)
参考了这篇博客：
Keras中间层输出的两种方式，及特征图可视化
谢谢！
