Tensorflow-CNN学习以及实现
2017-07-15 13:51
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代码参数解释
卷积操作
tf.nn.conv2d(input, filter, strides, padding, use_cudnn_on_gpu=None, name=None)
input:待卷积的数据。格式要求为一个张量,[batch, in_height, in_width, in_channels].
分别表示 批次数,图像高度,宽度,输入通道数。
filter: 卷积核。格式要求为[filter_height, filter_width, in_channels, out_channels].
分别表示 卷积核的高度,宽度,输入通道数,输出通道数。
strides :一个长为4的list. 表示每次卷积以后卷积窗口在input中滑动的距离
padding :有SAME和VALID两种选项,表示是否要保留图像边上那一圈不完全卷积的部分。如果是SAME,则保留
use_cudnn_on_gpu :是否使用cudnn加速。默认是True
池化操作
tf.nn.max_pool进行最大值池化操作,而avg_pool 则进行平均值池化操作.函数的定义为:
max_pool(value, ksize, strides, padding, data_format="NHWC", name=None):
value: 一个4D张量,格式为[batch, height, width, channels],与conv2d中input格式一样
ksize: 长为4的list,表示池化窗口的尺寸
strides: 池化窗口的滑动值,与conv2d中的一样
padding: 与conv2d中用法一样。
代码实现以及解释
import tensorflow as tf # Import MNIST data from tensorflow.examples.tutorials.mnist import input_data mnist = input_data.read_data_sets("/tmp/data/", one_hot=True) # Parameters learning_rate = 0.001 training_iters = 200000 batch_size = 128 display_step = 10 # Network Parameters n_input = 784 # MNIST data input (img shape: 28*28) n_classes = 10 # MNIST total classes (0-9 digits) dropout = 0.75 # Dropout, probability to keep units # tf Graph input x = tf.placeholder(tf.float32, [None, n_input]) y = tf.placeholder(tf.float32, [None, n_classes]) keep_prob = tf.placeholder(tf.float32) #dropout (keep probability) # Create some wrappers for simplicity def conv2d(x, W, b, strides=1): # Conv2D wrapper, with bias and relu activation # 结果返回一个Tensor,这个输出是feature map,shape仍然是[batch, height, width, channels]这种形式。 # 第二个参数(W):参数含义:[卷积核的高度,卷积核的宽度,图像通道数,卷积核个数] x = tf.nn.conv2d(x, W, strides=[1, strides, strides, 1], padding='SAME') x = tf.nn.bias_add(x, b) return tf.nn.relu(x) #最大池化,池化也有窗口,有滑动步长 def maxpool2d(x, k=2): # MaxPool2D wrapper return tf.nn.max_pool(x, ksize=[1, k, k, 1], strides=[1, k, k, 1], padding='SAME') # Create model def conv_net(x, weights, biases, dropout): # Reshape input picture x = tf.reshape(x, shape=[-1, 28, 28, 1]) #第一层,输入x是28*28,通道数为1,输出通道为32,即feature map 数目为32 # 又因为strides=[1,1,1,1] 所以单个通道的输出尺寸应该跟输入图像一样(为了保持输入和输出一样,在最边和上面补充0)。即总的卷积输出应该为?*28*28*32 # 也就是单个通道输出为28*28,共有32个通道,共有?个批次 # 在池化阶段,ksize=[1,2,2,1] 那么卷积结果经过池化以后的结果,其尺寸应该是?*14*14*32 # Convolution Layer conv1 = conv2d(x, weights['wc1'], biases['bc1']) # Max Pooling (down-sampling) conv1 = maxpool2d(conv1, k=2) #第二层 # 卷积核5*5,输入通道为32,输出通道为64。 # 卷积前图像的尺寸为 ?*14*14*32, 卷积后为?*14*14*64 # 池化后,输出的图像尺寸为?*7*7*64 # Convolution Layer conv2 = conv2d(conv1, weights['wc2'], biases['bc2']) # Max Pooling (down-sampling) conv2 = maxpool2d(conv2, k=2) # 第三层,是个全连接层, 输入维数7 * 7 * 64, 输出维数为1024 # Fully connected layer # Reshape conv2 output to fit fully connected layer input fc1 = tf.reshape(conv2, [-1, weights['wd1'].get_shape().as_list()[0]]) fc1 = tf.add(tf.matmul(fc1, weights['wd1']), biases['bd1']) fc1 = tf.nn.relu(fc1) # 这里使用了drop out,即随机安排一些cell输出值为0,可以防止过拟合 # Apply Dropout fc1 = tf.nn.dropout(fc1, dropout) # 第四层,输入1024维,输出10维,也就是具体的0~9分类 # Output, class prediction out = tf.add(tf.matmul(fc1, weights['out']), biases['out']) return out # Store layers weight & bias # 这里的weight就是卷积核,卷积核就是要学习的参数(个人理解,不到位请指点) weights = { # 5x5 conv, 1 input, 32 outputs # 'wc1': tf.Variable(tf.random_normal([5, 5, 1, 32])), # 5x5 conv, 32 inputs, 64 outputs 'wc2': tf.Variable(tf.random_normal([5, 5, 32, 64])), # fully connected, 7*7*64 inputs, 1024 outputs 'wd1': tf.Variable(tf.random_normal([7*7*64, 1024])), # 1024 inputs, 10 outputs (class prediction) 'out': tf.Variable(tf.random_normal([1024, n_classes])) } biases = { 'bc1': tf.Variable(tf.random_normal([32])), 'bc2': tf.Variable(tf.random_normal([64])), 'bd1': tf.Variable(tf.random_normal([1024])), 'out': tf.Variable(tf.random_normal([n_classes])) } # Construct model pred = conv_net(x, weights, biases, keep_prob) # Define loss and optimizer cost = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(logits=pred, labels=y)) optimizer = tf.train.AdamOptimizer(learning_rate=learning_rate).minimize(cost) # Evaluate model correct_pred = tf.equal(tf.argmax(pred, 1), tf.argmax(y, 1)) accuracy = tf.reduce_mean(tf.cast(correct_pred, tf.float32)) # Initializing the variables init = tf.global_variables_initializer() # Launch the graph with tf.Session() as sess: sess.run(init) step = 1 # Keep training until reach max iterations while step * batch_size < training_iters: batch_x, batch_y = mnist.train.next_batch(batch_size) # Run optimization op (backprop) sess.run(optimizer, feed_dict={x: batch_x, y: batch_y, keep_prob: dropout}) if step % display_step == 0: # Calculate batch loss and accuracy loss, acc = sess.run([cost, accuracy], feed_dict={x: batch_x, y: batch_y, keep_prob: 1.}) print("Iter " + str(step*batch_size) + ", Minibatch Loss= " + \ "{:.6f}".format(loss) + ", Training Accuracy= " + \ "{:.5f}".format(acc)) step += 1 print("Optimization Finished!") # Calculate accuracy for 256 mnist test images print("Testing Accuracy:", sess.run(accuracy, feed_dict={x: mnist.test.images[:256], y: mnist.test.labels[:256], keep_prob: 1.}))
代码运行结果
数据集为MNIST相关文章推荐
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