Building the CNN MNIST Classifier - 2.5 English

Create a file called low_level_cnn.py, and add the following code:

import os
os.environ['TF_CPP_MIN_LOG_LEVEL']='2'
import tensorflow as tf
from data_utils import get_one_shot_test_data

TEST_BATCH=100

def conv_relu(inputs, filters, k_size, stride, padding, scope_name):
    '''
    A method that does convolution + relu on inputs
    '''
    with tf.variable_scope(scope_name, reuse=tf.AUTO_REUSE) as scope:
        in_channels = inputs.shape[-1]
        kernel = tf.get_variable('kernel', 
                                [k_size, k_size, in_channels, filters], 
                                initializer=tf.truncated_normal_initializer())
        biases = tf.get_variable('biases', 
                                [filters],
                                initializer=tf.random_normal_initializer())
        conv = tf.nn.conv2d(inputs, kernel, strides=[1, stride, stride, 1], padding=padding)
    return tf.nn.relu(tf.nn.bias_add(conv, biases), name=scope.name)

def maxpool(inputs, ksize, stride, padding='VALID', scope_name='pool'):
    '''A method that does max pooling on inputs'''
    with tf.variable_scope(scope_name, reuse=tf.AUTO_REUSE) as scope:
        pool = tf.nn.max_pool(inputs, 
                            ksize=[1, ksize, ksize, 1], 
                            strides=[1, stride, stride, 1],
                            padding=padding)
    return pool

def fully_connected(inputs, out_dim, scope_name='fc'):
    '''
    A fully connected linear layer on inputs
    '''
    with tf.variable_scope(scope_name, reuse=tf.AUTO_REUSE) as scope:
        in_dim = inputs.shape[-1]
        w = tf.get_variable('weights', [in_dim, out_dim],
                            initializer=tf.truncated_normal_initializer())
        b = tf.get_variable('b', [out_dim],
                            initializer=tf.constant_initializer(0.0))
        out = tf.matmul(inputs, w) + b
    return out

def net_fn(image, n_classes=10, keep_prob=0.5, is_training=True):
    conv1 = conv_relu(inputs=image,
                    filters=32,
                    k_size=5,
                    stride=1,
                    padding='SAME',
                    scope_name='conv1')
    pool1 = maxpool(conv1, 2, 2, 'VALID', 'pool1')
    conv2 = conv_relu(inputs=pool1,
                    filters=64,
                    k_size=5,
                    stride=1,
                    padding='SAME',
                    scope_name='conv2')
    pool2 = maxpool(conv2, 2, 2, 'VALID', 'pool2')
    feature_dim = pool2.shape[1] * pool2.shape[2] * pool2.shape[3]
    pool2 = tf.reshape(pool2, [-1, feature_dim])
    fc = fully_connected(pool2, 1024, 'fc')
    keep_prob = keep_prob if is_training else 1
    dropout = tf.nn.dropout(tf.nn.relu(fc), keep_prob, name='relu_dropout')
    logits = fully_connected(dropout, n_classes, 'logits')
    return logits
net_fn.default_image_size=28

def model_fn():
  tf.logging.set_verbosity(tf.logging.INFO)
  img, labels = get_one_shot_test_data(TEST_BATCH)

  logits = net_fn(img, is_training=False)
  predictions = tf.argmax(logits, 1)
  labels = tf.argmax(labels, 1)
  eval_metric_ops = {
      'accuracy': tf.metrics.accuracy(labels, predictions),
      'recall_5': tf.metrics.recall_at_k(labels, logits, 5)
  }
  return eval_metric_ops

The net_fn function defines the network architecture. It takes the MNIST image data as argument and return a logits tensor. The model_fn function reads an input data pipeline and returns a dictionary of evaluation metrics operations.