TensorFlow (四): MNIST CNN实现

系统管理员 2022-03-12 11:46 297阅读 0赞

### MNIST CNN实现 ###

*  准备工作
 *   *  mnist\_loader.py
 *  代码
 *  效果图
 *  总结

# 准备工作 #

## mnist\_loader.py ##

def load_mnist(path, kind='train'):
        import os
        import gzip
        import numpy as np
    
        """Load MNIST data from `path`"""
        labels_path = os.path.join(path,
                                   '%s-labels-idx1-ubyte.gz'
                                   % kind)
        images_path = os.path.join(path,
                                   '%s-images-idx3-ubyte.gz'
                                   % kind)
    
        with gzip.open(labels_path, 'rb') as lbpath:
            labels = np.frombuffer(lbpath.read(), dtype=np.uint8,
                                   offset=8)
    
        with gzip.open(images_path, 'rb') as imgpath:
            images = np.frombuffer(imgpath.read(), dtype=np.uint8,
                                   offset=16).reshape(len(labels), 784)
    
        return images, labels

# 代码 #

import matplotlib.pyplot as plt 
    import numpy as np 
    import tensorflow as tf 
    from tensorflow import keras 
    import mnist_loader as ml 
    
    def load_data():
    	x_train, y_train = ml.load_mnist('./MNIST_DATA', 'train')
    	x_test, y_test = ml.load_mnist('./MNIST_DATA', 't10k')
    
    	x_train = x_train.reshape(-1, 28, 28, 1) / 255.0
    	x_test = x_test.reshape(-1, 28, 28, 1) / 255.0
    	y_train = keras.utils.to_categorical(y_train)
    	y_test = keras.utils.to_categorical(y_test)
    	return x_train, y_train, x_test, y_test
    
    def rand_weights(shape):
    	return tf.Variable(tf.truncated_normal(shape, stddev = 0.05))
    
    def rand_biases(length):
    	return tf.Variable(tf.truncated_normal([length], stddev = 0.05))
    
    def new_conv_layer(input, nb_filters, nb_channels = 1, filter_size = 3, activation = tf.nn.relu):
    	shape = [filter_size, filter_size, nb_channels, nb_filters]
    
    	w = rand_weights(shape)
    	b = rand_biases(nb_filters)
    
    	layer = tf.nn.conv2d(input = input, filter = w, strides = [1, 1, 1, 1], padding = "SAME")
    
    	layer = layer + b
    
    	layer = activation(layer)
    
    	return layer
    
    def new_max_pooling_layer(input, size = 2):
    
    	layer = tf.nn.max_pool(value = input, ksize = [1, size, size, 1], strides = [1, size, size, 1], padding = "SAME")
    	return layer
    
    def flatten_layer(input):
    
    	nb_features = (input.get_shape())[1:].num_elements()
    
    	layer = tf.reshape(input, [-1, nb_features])
    
    	return layer
    
    def new_fc_layer(input, nb_outputs):
    
    	nb_inputs = (input.get_shape())[1:].num_elements()
    
    	layer = tf.matmul(input, rand_weights([nb_inputs, nb_outputs])) + rand_biases(nb_outputs)
    
    	return layer
    
    def main(arg = None):
    	x_train, y_train, x_test, y_test = load_data()
    
    	nb_classes = 10
    	learning_rate = 0.1
    	nb_epochs = 1000
    	batch_size = 128
    
    	acc_history = []
    	loss_history = []
    
    	with tf.Graph().as_default():
    		x = tf.placeholder(dtype = tf.float32, shape = [None, 28, 28, 1])
    		y_ = tf.placeholder(dtype = tf.float32, shape = [None, nb_classes])
    
    		c1 = new_conv_layer(x, 32)
    		p1 = new_max_pooling_layer(c1)
    		c2 = new_conv_layer(p1, 64, nb_channels = 32)
    		flatten = flatten_layer(c2)
    		fc1 = new_fc_layer(flatten, 128)
    		logits = new_fc_layer(fc1, nb_classes)
    
    		loss = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits_v2(labels = y_, logits = logits))
    		train = tf.train.GradientDescentOptimizer(learning_rate).minimize(loss)
    		accuracy = tf.reduce_mean(tf.cast(tf.equal(tf.argmax(tf.nn.softmax(logits), axis = 1), tf.argmax(y_, axis = 1)), tf.float32))
    
    		with tf.Session() as sess:
    			sess.run(tf.global_variables_initializer())
    			indices = np.arange(x_train.shape[0])
    			for epoch in range(nb_epochs):
    				np.random.shuffle(indices)
    				x_batch = x_train[indices[:batch_size]]
    				y_batch = y_train[indices[:batch_size]]
    				feed_dict = { x: x_batch, y_: y_batch}
    				sess.run([train], feed_dict = feed_dict)
    				if epoch % 10 == 0:
    					l, acc = sess.run([loss, accuracy], feed_dict = feed_dict)
    					print("epoch: %d loss: %f, accuracy: %f" % (epoch, l, acc))
    				loss_history.append(l)
    				acc_history.append(acc)
    
    			test_acc = sess.run(accuracy, feed_dict = { x: x_test, y_: y_test})
    			print("test accuracy: %f" % test_acc)
    			saver = tf.train.Saver()
    			saver.save(sess, './cnn.ckpt', global_step = nb_epochs)
    
    		plt.plot(loss_history)
    		plt.plot(acc_history)
    		plt.legend(["loss", "accuracy"])
    		plt.show()
    
    if __name__ == '__main__':
    	tf.app.run()

# 效果图 #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpbmNlZWVfXw_size_16_color_FFFFFF_t_70][]

# 总结 #

对于如此大量的数据 (6W), 使用 Batch Gradient Descent 显然工作量太过沉重, 所以我使用了 Mini Batch Gradient Descent, 以 128 为一组, 在训练了大概 1000 个 epoch 之后模型收敛, 最终的 test accuracy 为 97.23%.  
相比于 Keras, 直接用 TensorFlow 来构建神经网络确实十分繁琐, 但是一旦你熟悉了它的API之后, 又觉得还可以接受.

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