TFRecords:将张量列表写入单个示例

问题描述

我正在使用卷积神经网络从图像中提取特征.所讨论的网络具有三个大小不同的输出(三个输出张量).我想将提取的特征存储在 TFRecords 中，每个图像一个示例:

I'm extracting features from images using a convolutional neural network. The network in question has three outputs (three output tensors), which differ in size. I want to store the extracted features in TFRecords, one Example for each image:

Example:
    image_id: 1
    features/fc8: [output1.1, output1.2, output1.3]
Example:
    image_id: 2
    features/fc8: [output2.1, output2.2, output2.3]
....

如何使用 TFRecords 实现这种结构?

How can I achieve this structure using TFRecords?

推荐答案

优雅的方式是使用 tf.SequenceExample.

Elegant way is to use tf.SequenceExample.

1. 使用 tf.SequenceExample() 格式转换数据

def make_example(features, image_id):

  ex = tf.train.SequenceExample()   
  ex.context.feature['image_id'].int64_list.value.append(image_id)
  fl_features = ex.feature_lists.feature_list['features/fc8']

  for feature in features:
    fl_features.feature.add().bytes_list.value.append(frame.tostring())
  return ex   

写入 TFRecord

def _convert_to_tfrecord(output_file, feature_batch, ids_batch):

  writer = tf.python_io.TFRecordWriter(output_file)

  for features, id in zip(feature_batch, ids_batch):
    ex = make_example(features, id)
    writer.write(ex.SerializeToString())
  writer.close()

解析示例

def parse_example_proto(example_serialized):

 context_features = {
    'image_id': tf.FixedLenFeature([], dtype=tf.int64)}
 sequence_features = {
    'features/fc8': tf.FixedLenSequenceFeature([], dtype=tf.string)}

 context_parsed, sequence_parsed = tf.parse_single_sequence_example(
    serialized=example_serialized,
    context_features=context_features,
    sequence_features=sequence_features)
 return context_parsed['image_id'], sequence_features['features/fc8']

注意:这里的特征保存在byte_list中，也可以保存在float_list中.
另一种方法是使用 tf.parse_single_example() 将示例存储为:

Note: The features here are saved in byte_list, you can also save it in float_list.
Another way, is to use tf.parse_single_example() by storing the examples as:

image_id: 1  
features/fc8_1: output1.1  
features/fc8_2: output1.2  
features/fc8_3: output1.3  

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