斯坦福大学人工智能实验室李飞飞教授，实现人工智能3要素：语法(syntax)、语义(semantics)、推理(inference)。语言、视觉。通过语法(语言语法解析、视觉三维结构解析)和语义(语言语义、视觉特体动作含义)作模型输入训练数据，实现推理能力，训练学习能力应用到工作，从新数据推断结论。《The Syntax,Semantics and Inference Mechanism in Natureal Language》 http://www.aaai.org/Papers/Symposia/Fall/1996/FS-96-04/FS96-04-010.pdf 。

看图说话模型。输入一张图片，根据图像像给出描述图像内容自然语言，讲故事。翻译图像信息和文本信息。https://github.com/tensorflow/models/tree/master/research/im2txt 。

原理。编码器-解码器框架，图像编码成固定中间矢量，解码成自然语言描述。编码器Inception V3图像识别模型，解码器LSTM网络。{s0,s1,…,sn-1}字幕词，{wes0,wes1,…,wesn-1}对应词嵌入向量，LSTM输出{p1,p2,…,pn}句子下一词生成概率分布，{logp1(s1),logp2(s2),…,logpn(sn)}正确词每个步骤对数似然，总和取负数是模型最小化目标。

最佳实践。微软Microsoft COCO Caption数据集 http://mscoco.org/ 。Miscrosoft Common Objects in Context(COCO)数据集。超过30万张图片，200万个标记实体。对原COCO数据集33万张图片，用亚马逊Mechanical Turk服务，人工为每张图片生成至少5句标注，标注语句超过150万句。2014版本、2015版本。2014版本82783张图片，验证集40504张图片，测试集40775张图片。 TensorFlow-Slim图像分类库 https://github.com/tensorflow/models/tree/master/research/inception/inception/slim 。

构建模型。showandtell_model.py。

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import tensorflow as tf
from im2txt.ops import image_embedding
from im2txt.ops import image_processing
from im2txt.ops import inputs as input_ops
class ShowAndTellModel(object):
  """Image-to-text implementation based on http://arxiv.org/abs/1411.4555.
  "Show and Tell: A Neural Image Caption Generator"
  Oriol Vinyals, Alexander Toshev, Samy Bengio, Dumitru Erhan
  """
  def __init__(self, config, mode, train_inception=False):
    """Basic setup.
    Args:
      config: Object containing configuration parameters.
      mode: "train", "eval" or "inference".
      train_inception: Whether the inception submodel variables are trainable.
    """
    assert mode in ["train", "eval", "inference"]
    self.config = config
    self.mode = mode
    self.train_inception = train_inception
    # Reader for the input data.
    self.reader = tf.TFRecordReader()
    # To match the "Show and Tell" paper we initialize all variables with a
    # random uniform initializer.
    self.initializer = tf.random_uniform_initializer(
        minval=-self.config.initializer_scale,
        maxval=self.config.initializer_scale)
    # A float32 Tensor with shape [batch_size, height, width, channels].
    self.images = None
    # An int32 Tensor with shape [batch_size, padded_length].
    self.input_seqs = None
    # An int32 Tensor with shape [batch_size, padded_length].
    self.target_seqs = None
    # An int32 0/1 Tensor with shape [batch_size, padded_length].
    self.input_mask = None
    # A float32 Tensor with shape [batch_size, embedding_size].
    self.image_embeddings = None
    # A float32 Tensor with shape [batch_size, padded_length, embedding_size].
    self.seq_embeddings = None
    # A float32 scalar Tensor; the total loss for the trainer to optimize.
    self.total_loss = None
    # A float32 Tensor with shape [batch_size * padded_length].
    self.target_cross_entropy_losses = None
    # A float32 Tensor with shape [batch_size * padded_length].
    self.target_cross_entropy_loss_weights = None
    # Collection of variables from the inception submodel.
    self.inception_variables = []
    # Function to restore the inception submodel from checkpoint.
    self.init_fn = None
    # Global step Tensor.
    self.global_step = None
  def is_training(self):
    """Returns true if the model is built for training mode."""
    return self.mode == "train"
  def process_image(self, encoded_image, thread_id=0):
    """Decodes and processes an image string.
    Args:
      encoded_image: A scalar string Tensor; the encoded image.
      thread_id: Preprocessing thread id used to select the ordering of color
        distortions.
    Returns:
      A float32 Tensor of shape [height, width, 3]; the processed image.
    """
    return image_processing.process_image(encoded_image,
                                          is_training=self.is_training(),
                                          height=self.config.image_height,
                                          width=self.config.image_width,
                                          thread_id=thread_id,
                                          image_format=self.config.image_format)
  def build_inputs(self):
    """Input prefetching, preprocessing and batching.
    Outputs:
      self.images
      self.input_seqs
      self.target_seqs (training and eval only)
      self.input_mask (training and eval only)
    """
    if self.mode == "inference":
      # In inference mode, images and inputs are fed via placeholders.
      image_feed = tf.placeholder(dtype=tf.string, shape=[], name="image_feed")
      input_feed = tf.placeholder(dtype=tf.int64,
                                  shape=[None],  # batch_size
                                  name="input_feed")
      # Process image and insert batch dimensions.
      images = tf.expand_dims(self.process_image(image_feed), 0)
      input_seqs = tf.expand_dims(input_feed, 1)
      # No target sequences or input mask in inference mode.
      target_seqs = None
      input_mask = None
    else:
      # Prefetch serialized SequenceExample protos.
      input_queue = input_ops.prefetch_input_data(
          self.reader,
          self.config.input_file_pattern,
          is_training=self.is_training(),
          batch_size=self.config.batch_size,
          values_per_shard=self.config.values_per_input_shard,
          input_queue_capacity_factor=self.config.input_queue_capacity_factor,
          num_reader_threads=self.config.num_input_reader_threads)
      # Image processing and random distortion. Split across multiple threads
      # with each thread applying a slightly different distortion.
      assert self.config.num_preprocess_threads % 2 == 0
      images_and_captions = []
      for thread_id in range(self.config.num_preprocess_threads):
        serialized_sequence_example = input_queue.dequeue()
        encoded_image, caption = input_ops.parse_sequence_example(
            serialized_sequence_example,
            image_feature=self.config.image_feature_name,
            caption_feature=self.config.caption_feature_name)
        image = self.process_image(encoded_image, thread_id=thread_id)
        images_and_captions.append([image, caption])
      # Batch inputs.
      queue_capacity = (2 * self.config.num_preprocess_threads *
                        self.config.batch_size)
      images, input_seqs, target_seqs, input_mask = (
          input_ops.batch_with_dynamic_pad(images_and_captions,
                                           batch_size=self.config.batch_size,
                                           queue_capacity=queue_capacity))
    self.images = images
    self.input_seqs = input_seqs
    self.target_seqs = target_seqs
    self.input_mask = input_mask
  def build_image_embeddings(self):
    """Builds the image model subgraph and generates image embeddings.
    Inputs:
      self.images
    Outputs:
      self.image_embeddings
    """
    inception_output = image_embedding.inception_v3(
        self.images,
        trainable=self.train_inception,
        is_training=self.is_training())
    self.inception_variables = tf.get_collection(
        tf.GraphKeys.GLOBAL_VARIABLES, scope="InceptionV3")
    # Map inception output into embedding space.
    with tf.variable_scope("image_embedding") as scope:
      image_embeddings = tf.contrib.layers.fully_connected(
          inputs=inception_output,
          num_outputs=self.config.embedding_size,
          activation_fn=None,
          weights_initializer=self.initializer,
          biases_initializer=None,
          scope=scope)
    # Save the embedding size in the graph.
    tf.constant(self.config.embedding_size, name="embedding_size")
    self.image_embeddings = image_embeddings
  def build_seq_embeddings(self):
    """Builds the input sequence embeddings.
    Inputs:
      self.input_seqs
    Outputs:
      self.seq_embeddings
    """
    with tf.variable_scope("seq_embedding"), tf.device("/cpu:0"):
      embedding_map = tf.get_variable(
          name="map",
          shape=[self.config.vocab_size, self.config.embedding_size],
          initializer=self.initializer)
      seq_embeddings = tf.nn.embedding_lookup(embedding_map, self.input_seqs)
    self.seq_embeddings = seq_embeddings
  def build_model(self):
    """Builds the model.
    Inputs:
      self.image_embeddings
      self.seq_embeddings
      self.target_seqs (training and eval only)
      self.input_mask (training and eval only)
    Outputs:
      self.total_loss (training and eval only)
      self.target_cross_entropy_losses (training and eval only)
      self.target_cross_entropy_loss_weights (training and eval only)
    """
    # This LSTM cell has biases and outputs tanh(new_c) * sigmoid(o), but the
    # modified LSTM in the "Show and Tell" paper has no biases and outputs
    # new_c * sigmoid(o).
    lstm_cell = tf.contrib.rnn.BasicLSTMCell(
        num_units=self.config.num_lstm_units, state_is_tuple=True)
    if self.mode == "train":
      lstm_cell = tf.contrib.rnn.DropoutWrapper(
          lstm_cell,
          input_keep_prob=self.config.lstm_dropout_keep_prob,
          output_keep_prob=self.config.lstm_dropout_keep_prob)
    with tf.variable_scope("lstm", initializer=self.initializer) as lstm_scope:
      # Feed the image embeddings to set the initial LSTM state.
      zero_state = lstm_cell.zero_state(
          batch_size=self.image_embeddings.get_shape()[0], dtype=tf.float32)
      _, initial_state = lstm_cell(self.image_embeddings, zero_state)
      # Allow the LSTM variables to be reused.
      lstm_scope.reuse_variables()
      if self.mode == "inference":
        # In inference mode, use concatenated states for convenient feeding and
        # fetching.
        tf.concat(axis=1, values=initial_state, name="initial_state")
        # Placeholder for feeding a batch of concatenated states.
        state_feed = tf.placeholder(dtype=tf.float32,
                                    shape=[None, sum(lstm_cell.state_size)],
                                    name="state_feed")
        state_tuple = tf.split(value=state_feed, num_or_size_splits=2, axis=1)
        # Run a single LSTM step.
        lstm_outputs, state_tuple = lstm_cell(
            inputs=tf.squeeze(self.seq_embeddings, axis=[1]),
            state=state_tuple)
        # Concatentate the resulting state.
        tf.concat(axis=1, values=state_tuple, name="state")
      else:
        # Run the batch of sequence embeddings through the LSTM.
        sequence_length = tf.reduce_sum(self.input_mask, 1)
        lstm_outputs, _ = tf.nn.dynamic_rnn(cell=lstm_cell,
                                            inputs=self.seq_embeddings,
                                            sequence_length=sequence_length,
                                            initial_state=initial_state,
                                            dtype=tf.float32,
                                            scope=lstm_scope)
    # Stack batches vertically.
    lstm_outputs = tf.reshape(lstm_outputs, [-1, lstm_cell.output_size])
    with tf.variable_scope("logits") as logits_scope:
      logits = tf.contrib.layers.fully_connected(
          inputs=lstm_outputs,
          num_outputs=self.config.vocab_size,
          activation_fn=None,
          weights_initializer=self.initializer,
          scope=logits_scope)
    if self.mode == "inference":
      tf.nn.softmax(logits, name="softmax")
    else:
      targets = tf.reshape(self.target_seqs, [-1])
      weights = tf.to_float(tf.reshape(self.input_mask, [-1]))
      # Compute losses.
      losses = tf.nn.sparse_softmax_cross_entropy_with_logits(labels=targets,
                                                              logits=logits)
      batch_loss = tf.div(tf.reduce_sum(tf.multiply(losses, weights)),
                          tf.reduce_sum(weights),
                          name="batch_loss")
      tf.losses.add_loss(batch_loss)
      total_loss = tf.losses.get_total_loss()
      # Add summaries.
      tf.summary.scalar("losses/batch_loss", batch_loss)
      tf.summary.scalar("losses/total_loss", total_loss)
      for var in tf.trainable_variables():
        tf.summary.histogram("parameters/" + var.op.name, var)
      self.total_loss = total_loss
      self.target_cross_entropy_losses = losses  # Used in evaluation.
      self.target_cross_entropy_loss_weights = weights  # Used in evaluation.
  def setup_inception_initializer(self):
    """Sets up the function to restore inception variables from checkpoint."""
    if self.mode != "inference":
      # Restore inception variables only.
      saver = tf.train.Saver(self.inception_variables)
      def restore_fn(sess):
        tf.logging.info("Restoring Inception variables from checkpoint file %s",
                        self.config.inception_checkpoint_file)
        saver.restore(sess, self.config.inception_checkpoint_file)
      self.init_fn = restore_fn
  def setup_global_step(self):
    """Sets up the global step Tensor."""
    global_step = tf.Variable(
        initial_value=0,
        name="global_step",
        trainable=False,
        collections=[tf.GraphKeys.GLOBAL_STEP, tf.GraphKeys.GLOBAL_VARIABLES])
    self.global_step = global_step
  def build(self):
    """Creates all ops for training and evaluation."""
    # 构建模型
    self.build_inputs() # 构建输入数据
    self.build_image_embeddings() # 采用Inception V3构建图像模型，输出图片嵌入向量
    self.build_seq_embeddings() # 构建输入序列embeddings
    self.build_model() # CNN、LSTM串联，构建完整模型
    self.setup_inception_initializer() # 载入Inception V3预训练模型
    self.setup_global_step() # 记录全局迭代次数

训练模型。train.py。

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import tensorflow as tf
from im2txt import configuration
from im2txt import show_and_tell_model
FLAGS = tf.app.flags.FLAGS
tf.flags.DEFINE_string("input_file_pattern", "",
                       "File pattern of sharded TFRecord input files.")
tf.flags.DEFINE_string("inception_checkpoint_file", "",
                       "Path to a pretrained inception_v3 model.")
tf.flags.DEFINE_string("train_dir", "",
                       "Directory for saving and loading model checkpoints.")
tf.flags.DEFINE_boolean("train_inception", False,
                        "Whether to train inception submodel variables.")
tf.flags.DEFINE_integer("number_of_steps", 1000000, "Number of training steps.")
tf.flags.DEFINE_integer("log_every_n_steps", 1,
                        "Frequency at which loss and global step are logged.")
tf.logging.set_verbosity(tf.logging.INFO)
def main(unused_argv):
  assert FLAGS.input_file_pattern, "--input_file_pattern is required"
  assert FLAGS.train_dir, "--train_dir is required"
  model_config = configuration.ModelConfig()
  model_config.input_file_pattern = FLAGS.input_file_pattern
  model_config.inception_checkpoint_file = FLAGS.inception_checkpoint_file
  training_config = configuration.TrainingConfig()
  # Create training directory.
  # 创建训练结果存储路径
  train_dir = FLAGS.train_dir
  if not tf.gfile.IsDirectory(train_dir):
    tf.logging.info("Creating training directory: %s", train_dir)
    tf.gfile.MakeDirs(train_dir)
  # Build the TensorFlow graph.
  # 建立TensorFlow数据流图
  g = tf.Graph()
  with g.as_default():
    # Build the model.
    # 构建模型
    model = show_and_tell_model.ShowAndTellModel(
        model_config, mode="train", train_inception=FLAGS.train_inception)
    model.build()
    # Set up the learning rate.
    # 定义学习率
    learning_rate_decay_fn = None
    if FLAGS.train_inception:
      learning_rate = tf.constant(training_config.train_inception_learning_rate)
    else:
      learning_rate = tf.constant(training_config.initial_learning_rate)
      if training_config.learning_rate_decay_factor > 0:
        num_batches_per_epoch = (training_config.num_examples_per_epoch /
                                 model_config.batch_size)
        decay_steps = int(num_batches_per_epoch *
                          training_config.num_epochs_per_decay)
        def _learning_rate_decay_fn(learning_rate, global_step):
          return tf.train.exponential_decay(
              learning_rate,
              global_step,
              decay_steps=decay_steps,
              decay_rate=training_config.learning_rate_decay_factor,
              staircase=True)
        learning_rate_decay_fn = _learning_rate_decay_fn
    # Set up the training ops.
    # 定义训练操作
    train_op = tf.contrib.layers.optimize_loss(
        loss=model.total_loss,
        global_step=model.global_step,
        learning_rate=learning_rate,
        optimizer=training_config.optimizer,
        clip_gradients=training_config.clip_gradients,
        learning_rate_decay_fn=learning_rate_decay_fn)
    # Set up the Saver for saving and restoring model checkpoints.
    saver = tf.train.Saver(max_to_keep=training_config.max_checkpoints_to_keep)
  # Run training.
  # 训练
  tf.contrib.slim.learning.train(
      train_op,
      train_dir,
      log_every_n_steps=FLAGS.log_every_n_steps,
      graph=g,
      global_step=model.global_step,
      number_of_steps=FLAGS.number_of_steps,
      init_fn=model.init_fn,
      saver=saver)
if __name__ == "__main__":
  tf.app.run()

预测生成模型。run_inference.py。

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import math
import os
import tensorflow as tf
from im2txt import configuration
from im2txt import inference_wrapper
from im2txt.inference_utils import caption_generator
from im2txt.inference_utils import vocabulary
FLAGS = tf.flags.FLAGS
tf.flags.DEFINE_string("checkpoint_path", "",
                       "Model checkpoint file or directory containing a "
                       "model checkpoint file.")
tf.flags.DEFINE_string("vocab_file", "", "Text file containing the vocabulary.")
tf.flags.DEFINE_string("input_files", "",
                       "File pattern or comma-separated list of file patterns "
                       "of image files.")
tf.logging.set_verbosity(tf.logging.INFO)
def main(_):
  # Build the inference graph.
  g = tf.Graph()
  with g.as_default():
    model = inference_wrapper.InferenceWrapper()
    restore_fn = model.build_graph_from_config(configuration.ModelConfig(),
                                               FLAGS.checkpoint_path)
  g.finalize()
  # Create the vocabulary.
  vocab = vocabulary.Vocabulary(FLAGS.vocab_file)
  filenames = []
  for file_pattern in FLAGS.input_files.split(","):
    filenames.extend(tf.gfile.Glob(file_pattern))
  tf.logging.info("Running caption generation on %d files matching %s",
                  len(filenames), FLAGS.input_files)
  with tf.Session(graph=g) as sess:
    # Load the model from checkpoint.
    restore_fn(sess)
    # Prepare the caption generator. Here we are implicitly using the default
    # beam search parameters. See caption_generator.py for a description of the
    # available beam search parameters.
    generator = caption_generator.CaptionGenerator(model, vocab)
    for filename in filenames:
      with tf.gfile.GFile(filename, "r") as f:
        image = f.read()
      captions = generator.beam_search(sess, image)
      print("Captions for image %s:" % os.path.basename(filename))
      for i, caption in enumerate(captions):
        # Ignore begin and end words.
        sentence = [vocab.id_to_word(w) for w in caption.sentence[1:-1]]
        sentence = " ".join(sentence)
        print("  %d) %s (p=%f)" % (i, sentence, math.exp(caption.logprob)))
if __name__ == "__main__":
  tf.app.run()

参考资料： 《TensorFlow技术解析与实战》

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