Tensorflow Object Detection API 源码分析之 utils/label_map_util.py

Tensorflow Object Detection API 源码分析之 utils/label_map_util.py

protos/string_int_label_map.proto

syntax = "proto2";

package object_detection.protos;

message StringIntLabelMapItem {
  // String name. The most common practice is to set this to a MID or synsets
  // id.
  optional string name = 1;

  // Integer id that maps to the string name above. Label ids should start from
  // 1.
  optional int32 id = 2;

  // Human readable string label.
  optional string display_name = 3;
};

message StringIntLabelMap {
  repeated StringIntLabelMapItem item = 1;
};

utils/label_map_util.py

# 有关 label map 的辅助函数
"""Label map utility functions."""

import logging

import tensorflow as tf
from google.protobuf import text_format
from object_detection.protos import string_int_label_map_pb2


# background默认为0，所以其他的不能为0，否则报错
def _validate_label_map(label_map):
  """Checks if a label map is valid.

  Args:
    label_map: StringIntLabelMap to validate.

  Raises:
    ValueError: if label map is invalid.
  """
  for item in label_map.item:
    if item.id < 0:
      raise ValueError('Label map ids should be >= 0.')
    if (item.id == 0 and item.name != 'background' and
        item.display_name != 'background'):
      raise ValueError('Label map id 0 is reserved for the background label')


# 返回 类别 和 index 的字典  {key为index，value为类别id}
# 例如 category_index[1] = id ?
def create_category_index(categories):
  """Creates dictionary of COCO compatible categories keyed by category id.

  Args:
    categories: a list of dicts, each of which has the following keys:
      'id': (required) an integer id uniquely identifying this category.
      'name': (required) string representing category name
        e.g., 'cat', 'dog', 'pizza'.

  Returns:
    category_index: a dict containing the same entries as categories, but keyed
      by the 'id' field of each category.
  """
  category_index = {}
  for cat in categories:
    category_index[cat['id']] = cat
  return category_index

# 返回最大的index
def get_max_label_map_index(label_map):
  """Get maximum index in label map.

  Args:
    label_map: a StringIntLabelMapProto

  Returns:
    an integer
  """
  return max([item.id for item in label_map.item])


# 将label_map 转化为 categories 列表 [{'id': item.id, 'name': name} , ...]
# 可选 name 或者 display_name
def convert_label_map_to_categories(label_map,
                                    max_num_classes,
                                    use_display_name=True):
  """Loads label map proto and returns categories list compatible with eval.

  This function loads a label map and returns a list of dicts, each of which
  has the following keys:
    'id': (required) an integer id uniquely identifying this category.
    'name': (required) string representing category name
      e.g., 'cat', 'dog', 'pizza'.
  We only allow class into the list if its id-label_id_offset is
  between 0 (inclusive) and max_num_classes (exclusive).
  If there are several items mapping to the same id in the label map,
  we will only keep the first one in the categories list.

  Args:
    label_map: a StringIntLabelMapProto or None.  If None, a default categories
      list is created with max_num_classes categories.
    max_num_classes: maximum number of (consecutive) label indices to include.
    use_display_name: (boolean) choose whether to load 'display_name' field
      as category name.  If False or if the display_name field does not exist,
      uses 'name' field as category names instead.
  Returns:
    categories: a list of dictionaries representing all possible categories.
  """
  categories = []
  list_of_ids_already_added = []
  if not label_map:
    label_id_offset = 1
    for class_id in range(max_num_classes):
      categories.append({
          'id': class_id + label_id_offset,
          'name': 'category_{}'.format(class_id + label_id_offset)
      })
    return categories
  for item in label_map.item:
    if not 0 < item.id <= max_num_classes:
      logging.info('Ignore item %d since it falls outside of requested '
                   'label range.', item.id)
      continue
    if use_display_name and item.HasField('display_name'):
      name = item.display_name
    else:
      name = item.name
    if item.id not in list_of_ids_already_added:
      list_of_ids_already_added.append(item.id)
      categories.append({'id': item.id, 'name': name})
  return categories


# 从文件载入 label map，下一个函数使用
def load_labelmap(path):
  """Loads label map proto.

  Args:
    path: path to StringIntLabelMap proto text file.
  Returns:
    a StringIntLabelMapProto
  """
  with tf.gfile.GFile(path, 'r') as fid:
    label_map_string = fid.read()
    label_map = string_int_label_map_pb2.StringIntLabelMap()
    try:
      text_format.Merge(label_map_string, label_map)
    except text_format.ParseError:
      label_map.ParseFromString(label_map_string)
  _validate_label_map(label_map)
  return label_map


# 获取 label_map 字典，返回形式 label_map_dict['background'] = 0
def get_label_map_dict(label_map_path,
                       use_display_name=False,
                       fill_in_gaps_and_background=False):
  """Reads a label map and returns a dictionary of label names to id.

  Args:
    label_map_path: path to StringIntLabelMap proto text file.
    use_display_name: whether to use the label map items' display names as keys.
    fill_in_gaps_and_background: whether to fill in gaps and background with
    respect to the id field in the proto. The id: 0 is reserved for the
    'background' class and will be added if it is missing. All other missing
    ids in range(1, max(id)) will be added with a dummy class name
    ("class_") if they are missing.

  Returns:
    A dictionary mapping label names to id.

  Raises:
    ValueError: if fill_in_gaps_and_background and label_map has non-integer or
    negative values.
  """
  label_map = load_labelmap(label_map_path)
  label_map_dict = {}
  for item in label_map.item:
    if use_display_name:
      label_map_dict[item.display_name] = item.id
    else:
      label_map_dict[item.name] = item.id

  if fill_in_gaps_and_background:
    values = set(label_map_dict.values())

    if 0 not in values:
      label_map_dict['background'] = 0
    if not all(isinstance(value, int) for value in values):
      raise ValueError('The values in label map must be integers in order to'
                       'fill_in_gaps_and_background.')
    if not all(value >= 0 for value in values):
      raise ValueError('The values in the label map must be positive.')

    if len(values) != max(values) + 1:
      # there are gaps in the labels, fill in gaps.
      for value in range(1, max(values)):
        if value not in values:
          label_map_dict['class_' + str(value)] = value

  return label_map_dict


# 建立从类别索引 到 label_map的字典  
# {1: {'id': 1, 'name': 'dog'}, 2: {'id': 2, 'name': 'cat'}, ...}
# model_lib.py 中调用的函数，重要
def create_category_index_from_labelmap(label_map_path):
  """Reads a label map and returns a category index.

  Args:
    label_map_path: Path to `StringIntLabelMap` proto text file.

  Returns:
    A category index, which is a dictionary that maps integer ids to dicts
    containing categories, e.g.
    {1: {'id': 1, 'name': 'dog'}, 2: {'id': 2, 'name': 'cat'}, ...}
  """
  label_map = load_labelmap(label_map_path)
  max_num_classes = max(item.id for item in label_map.item)
  categories = convert_label_map_to_categories(label_map, max_num_classes)
  return create_category_index(categories)

# 建立类别无关的索引，只有一个object物体的类别
def create_class_agnostic_category_index():
  """Creates a category index with a single `object` class."""
  return {1: {'id': 1, 'name': 'object'}}