fsns.py

# -*- coding: utf-8 -*-
# Copyright 2017 The TensorFlow Authors All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

"""Configuration to read FSNS dataset https://goo.gl/3Ldm8v."""

import os
import re
import tensorflow as tf
from tensorflow.contrib import slim
import logging

DEFAULT_DATASET_DIR = os.path.join(os.path.dirname(__file__), 'data', 'fsns')

# The dataset configuration, should be used only as a default value.
DEFAULT_CONFIG = {
    'name': 'FSNS',
    'splits': {
        'train': {
            'size': 1044868,
            'pattern': 'train/train*'
        },
        'test': {
            'size': 20404,
            'pattern': 'test/test*'
        },
        'validation': {
            'size': 16150,
            'pattern': 'validation/validation*'
        }
    },
    'charset_filename': 'charset_size=134.txt',
    'image_shape': (150, 600, 3),
    'num_of_views': 4,
    'max_sequence_length': 37,
    'null_code': 133,
    'items_to_descriptions': {
        'image': 'A [150 x 600 x 3] color image.',
        'label': 'Characters codes.',
        'text': 'A unicode string.',
        'length': 'A length of the encoded text.',
        'num_of_views': 'A number of different views stored within the image.'
    }
}


def read_charset(filename, null_character=u'\u2591'):
  """Reads a charset definition from a tab separated text file.

  charset file has to have format compatible with the FSNS dataset.

  Args:
    filename: a path to the charset file.
    null_character: a unicode character used to replace '<null>' character. the
      default value is a light shade block '░'.

  Returns:
    a dictionary with keys equal to character codes and values - unicode
    characters.
  """
  pattern = re.compile(r'(\d+)\t(.+)')
  charset = {}
  with tf.io.gfile.GFile(filename) as f:
    for i, line in enumerate(f):
      m = pattern.match(line)
      if m is None:
        logging.warning('incorrect charset file. line #%d: %s', i, line)
        continue
      code = int(m.group(1))
      char = m.group(2)
      if char == '<nul>':
        char = null_character
      charset[code] = char
  return charset


class _NumOfViewsHandler(slim.tfexample_decoder.ItemHandler):
  """Convenience handler to determine number of views stored in an image."""

  def __init__(self, width_key, original_width_key, num_of_views):
    super(_NumOfViewsHandler, self).__init__([width_key, original_width_key])
    self._width_key = width_key
    self._original_width_key = original_width_key
    self._num_of_views = num_of_views

  def tensors_to_item(self, keys_to_tensors):
    return tf.cast(
        self._num_of_views * keys_to_tensors[self._original_width_key] /
        keys_to_tensors[self._width_key], dtype=tf.int64)


def get_split(split_name, dataset_dir=None, config=None):
  """Returns a dataset tuple for FSNS dataset.

  Args:
    split_name: A train/test split name.
    dataset_dir: The base directory of the dataset sources, by default it uses
      a predefined CNS path (see DEFAULT_DATASET_DIR).
    config: A dictionary with dataset configuration. If None - will use the
      DEFAULT_CONFIG.

  Returns:
    A `Dataset` namedtuple.

  Raises:
    ValueError: if `split_name` is not a valid train/test split.
  """
  if not dataset_dir:
    dataset_dir = DEFAULT_DATASET_DIR

  if not config:
    config = DEFAULT_CONFIG

  if split_name not in config['splits']:
    raise ValueError('split name %s was not recognized.' % split_name)

  logging.info('Using %s dataset split_name=%s dataset_dir=%s', config['name'],
               split_name, dataset_dir)

  # Ignores the 'image/height' feature.
  zero = tf.zeros([1], dtype=tf.int64)
  keys_to_features = {
      'image/encoded':
      tf.io.FixedLenFeature((), tf.string, default_value=''),
      'image/format':
      tf.io.FixedLenFeature((), tf.string, default_value='png'),
      'image/width':
      tf.io.FixedLenFeature([1], tf.int64, default_value=zero),
      'image/orig_width':
      tf.io.FixedLenFeature([1], tf.int64, default_value=zero),
      'image/class':
      tf.io.FixedLenFeature([config['max_sequence_length']], tf.int64),
      'image/unpadded_class':
      tf.io.VarLenFeature(tf.int64),
      'image/text':
      tf.io.FixedLenFeature([1], tf.string, default_value=''),
  }
  items_to_handlers = {
      'image':
      slim.tfexample_decoder.Image(
          shape=config['image_shape'],
          image_key='image/encoded',
          format_key='image/format'),
      'label':
      slim.tfexample_decoder.Tensor(tensor_key='image/class'),
      'text':
      slim.tfexample_decoder.Tensor(tensor_key='image/text'),
      'num_of_views':
      _NumOfViewsHandler(
          width_key='image/width',
          original_width_key='image/orig_width',
          num_of_views=config['num_of_views'])
  }
  decoder = slim.tfexample_decoder.TFExampleDecoder(keys_to_features,
                                                    items_to_handlers)
  charset_file = os.path.join(dataset_dir, config['charset_filename'])
  charset = read_charset(charset_file)
  file_pattern = os.path.join(dataset_dir,
                              config['splits'][split_name]['pattern'])
  return slim.dataset.Dataset(
      data_sources=file_pattern,
      reader=tf.compat.v1.TFRecordReader,
      decoder=decoder,
      num_samples=config['splits'][split_name]['size'],
      items_to_descriptions=config['items_to_descriptions'],
      #  additional parameters for convenience.
      charset=charset,
      charset_file=charset_file,
      image_shape=config['image_shape'],
      num_char_classes=len(charset),
      num_of_views=config['num_of_views'],
      max_sequence_length=config['max_sequence_length'],
      null_code=config['null_code'])