圖像常用的數據增強技術（based on TensorFlow）

數據作爲深度學習的基礎，其對模型性能的重要重要性不言而喻。在本文，我們將梳理下常用的圖像數據處理技術，至於具體的編程工具，選擇 Python + TensorFlow：

Tip：

如果你使用 tf.data 來組織你的圖像數據輸入管道，那麼恭喜您，直接在 map 中調用本文的代碼。

第一種

#coding:utf-8
# preprocess_lenet.py

"""
 Train
    step1: resize image with crop or pad
    step2: subtract 128.0
    step3: div 128.0
 Eval
    step1: resize image with crop or pad
    step2: subtract 128.0
    step3: div 128.0
"""

import tensorflow as tf


def preprocess_image(image, label, is_training, 
                     out_height=28, out_width=28):
  """Preprocesses the given image.

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    output_height: The height of the image after preprocessing.
    output_width: The width of the image after preprocessing.
    is_training: `True` if we're preprocessing the image for training and
      `False` otherwise.

  Returns:
    A preprocessed image.
  """
  image = tf.to_float(image)
  image = tf.image.resize_image_with_crop_or_pad(
      image, out_width, out_height)
  image = tf.subtract(image, 128.0)
  image = tf.div(image, 128.0)
  return image, label

第二種

#coding:utf-8
#preprocess_cifar.py

"""
 Train
    step1: if pad
    step2: random crop
    step3: random flip left right
    step4: random brightness
    step5: random contrast
    step6: per image standardization
 Eval
    step1: resize image with crop or pad
    step2: per image standardization
"""

import tensorflow as tf

_PADDING = 4


def preprocess_image(image, label, is_training, 
                     out_height=32, out_width=32,
                     add_image_summaries=False):
  """Preprocesses the given image.

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    output_height: The height of the image after preprocessing.
    output_width: The width of the image after preprocessing.
    is_training: `True` if we're preprocessing the image for training and
      `False` otherwise.
    add_image_summaries: Enable image summaries.

  Returns:
    A preprocessed image.
  """
  if is_training:
    image =  preprocess_for_train(
        image, out_height, out_width,
        add_image_summaries=add_image_summaries)
  else:
    image = preprocess_for_eval(
        image, out_height, out_width,
        add_image_summaries=add_image_summaries)
  return image, label


def preprocess_for_train(image,
                         output_height,
                         output_width,
                         padding=_PADDING,
                         add_image_summaries=True):
  """Preprocesses the given image for training.

  Note that the actual resizing scale is sampled from
    [`resize_size_min`, `resize_size_max`].

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    output_height: The height of the image after preprocessing.
    output_width: The width of the image after preprocessing.
    padding: The amound of padding before and after each dimension of the image.
    add_image_summaries: Enable image summaries.

  Returns:
    A preprocessed image.
  """
  if add_image_summaries:
    tf.summary.image('image', tf.expand_dims(image, 0))

  # Transform the image to floats.
  image = tf.to_float(image)
  if padding > 0:
    image = tf.pad(image, [[padding, padding], [padding, padding], [0, 0]])
  # Randomly crop a [height, width] section of the image.
  distorted_image = tf.random_crop(image,
                                   [output_height, output_width, 3])

  # Randomly flip the image horizontally.
  distorted_image = tf.image.random_flip_left_right(distorted_image)

  if add_image_summaries:
    tf.summary.image('distorted_image', tf.expand_dims(distorted_image, 0))

  # Because these operations are not commutative, consider randomizing
  # the order their operation.
  distorted_image = tf.image.random_brightness(distorted_image,
                                               max_delta=63)
  distorted_image = tf.image.random_contrast(distorted_image,
                                             lower=0.2, upper=1.8)
  # Subtract off the mean and divide by the variance of the pixels.
  return tf.image.per_image_standardization(distorted_image)


def preprocess_for_eval(image, output_height, output_width,
                        add_image_summaries=True):
  """Preprocesses the given image for evaluation.

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    output_height: The height of the image after preprocessing.
    output_width: The width of the image after preprocessing.
    add_image_summaries: Enable image summaries.

  Returns:
    A preprocessed image.
  """
  if add_image_summaries:
    tf.summary.image('image', tf.expand_dims(image, 0))
  # Transform the image to floats.
  image = tf.to_float(image)

  # Resize and crop if needed.
  resized_image = tf.image.resize_image_with_crop_or_pad(image,
                                                         output_width,
                                                         output_height)
  if add_image_summaries:
    tf.summary.image('resized_image', tf.expand_dims(resized_image, 0))

  # Subtract off the mean and divide by the variance of the pixels.
  return tf.image.per_image_standardization(resized_image)

第三種

#coding:utf-8
#preprocess_vgg.py

"""
 Train
    step1: _aspect_preserving_resize
           # 在不改變圖像寬高比的基礎上，
           # 將圖像的窄邊縮放到_RESIZE_SIDE_MIN和_RESIZE_SIDE_MAX之間
    step2: _random_crop
           # 將圖像隨機裁剪到 out_height, out_width
           # 如果out_height, out_width比縮放後的圖像大，報錯。
    step3: random flip left right
    step4: _mean_image_subtraction
           # RGB每個通道減去整個數據集的RGB通道的均值
 Eval
    step1: _aspect_preserving_resize
    step2: _central_crop
    step3: _mean_image_subtraction
"""

import tensorflow as tf

_R_MEAN = 123.68
_G_MEAN = 116.78
_B_MEAN = 103.94

_RESIZE_SIDE_MIN = 256
_RESIZE_SIDE_MAX = 512


def preprocess_image(image, label, is_training,
                     out_height=224, out_width=224,
                     resize_side_min=_RESIZE_SIDE_MIN,
                     resize_side_max=_RESIZE_SIDE_MAX):
  """Preprocesses the given image.

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    out_height: The height of the image after preprocessing.
    out_width: The width of the image after preprocessing.
    is_training: `True` if we're preprocessing the image for training and
      `False` otherwise.
    resize_side_min: The lower bound for the smallest side of the image for
      aspect-preserving resizing. If `is_training` is `False`, then this value
      is used for rescaling.
    resize_side_max: The upper bound for the smallest side of the image for
      aspect-preserving resizing. If `is_training` is `False`, this value is
      ignored. Otherwise, the resize side is sampled from
        [resize_size_min, resize_size_max].

  Returns:
    A preprocessed image.
  """
  if is_training:
    image = preprocess_for_train(image, out_height, out_width,
                                 resize_side_min, resize_side_max)
  else:
    image = preprocess_for_eval(image, out_height, out_width,
                                resize_side_min)
  return image, label


def preprocess_for_train(image,
                         out_height,
                         out_width,
                         resize_side_min=_RESIZE_SIDE_MIN,
                         resize_side_max=_RESIZE_SIDE_MAX):
  """Preprocesses the given image for training.

  Note that the actual resizing scale is sampled from
    [`resize_size_min`, `resize_size_max`].

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    out_height: The height of the image after preprocessing.
    out_width: The width of the image after preprocessing.
    resize_side_min: The lower bound for the smallest side of the image for
      aspect-preserving resizing.
    resize_side_max: The upper bound for the smallest side of the image for
      aspect-preserving resizing.

  Returns:
    A preprocessed image.
  """
  resize_side = tf.random_uniform(
      [], minval=resize_side_min, maxval=resize_side_max+1, dtype=tf.int32)

  image = _aspect_preserving_resize(image, resize_side)
  image = _random_crop([image], out_height, out_width)[0]
  image.set_shape([out_height, out_width, 3])
  image = tf.to_float(image)
  image = tf.image.random_flip_left_right(image)
  return _mean_image_subtraction(image, [_R_MEAN, _G_MEAN, _B_MEAN])


def preprocess_for_eval(image, out_height, out_width, resize_side):
  """Preprocesses the given image for evaluation.

  Args:
    image: A `Tensor` representing an image of arbitrary size.
    out_height: The height of the image after preprocessing.
    out_width: The width of the image after preprocessing.
    resize_side: The smallest side of the image for aspect-preserving resizing.

  Returns:
    A preprocessed image.
  """
  image = _aspect_preserving_resize(image, resize_side)
  image = _central_crop([image], out_height, out_width)[0]
  image.set_shape([out_height, out_width, 3])
  image = tf.to_float(image)
  return _mean_image_subtraction(image, [_R_MEAN, _G_MEAN, _B_MEAN])


def _aspect_preserving_resize(image, smallest_side):
  """Resize images preserving the original aspect ratio.

  Args:
    image: A 3-D image `Tensor`.
    smallest_side: A python integer or scalar `Tensor` indicating the size of
      the smallest side after resize.

  Returns:
    resized_image: A 3-D tensor containing the resized image.
  """
  smallest_side = tf.convert_to_tensor(smallest_side, dtype=tf.int32)

  shape = tf.shape(image)
  height = shape[0]
  width = shape[1]
  new_height, new_width = _smallest_size_at_least(height, width, smallest_side)
  image = tf.expand_dims(image, 0)
  resized_image = tf.image.resize_bilinear(image, [new_height, new_width],
                                           align_corners=False)
  resized_image = tf.squeeze(resized_image)
  resized_image.set_shape([None, None, 3])
  return resized_image


def _smallest_size_at_least(height, width, smallest_side):
  """Computes new shape with the smallest side equal to `smallest_side`.

  Computes new shape with the smallest side equal to `smallest_side` while
  preserving the original aspect ratio.

  Args:
    height: an int32 scalar tensor indicating the current height.
    width: an int32 scalar tensor indicating the current width.
    smallest_side: A python integer or scalar `Tensor` indicating the size of
      the smallest side after resize.

  Returns:
    new_height: an int32 scalar tensor indicating the new height.
    new_width: and int32 scalar tensor indicating the new width.
  """
  smallest_side = tf.convert_to_tensor(smallest_side, dtype=tf.int32)

  height = tf.to_float(height)
  width = tf.to_float(width)
  smallest_side = tf.to_float(smallest_side)

  scale = tf.cond(tf.greater(height, width),
                  lambda: smallest_side / width,
                  lambda: smallest_side / height)
  new_height = tf.to_int32(tf.rint(height * scale))
  new_width = tf.to_int32(tf.rint(width * scale))
  return new_height, new_width



def _random_crop(image_list, crop_height, crop_width):
  """Crops the given list of images.

  The function applies the same crop to each image in the list. This can be
  effectively applied when there are multiple image inputs of the same
  dimension such as:

    image, depths, normals = _random_crop([image, depths, normals], 120, 150)

  Args:
    image_list: a list of image tensors of the same dimension but possibly
      varying channel.
    crop_height: the new height.
    crop_width: the new width.

  Returns:
    the image_list with cropped images.

  Raises:
    ValueError: if there are multiple image inputs provided with different size
      or the images are smaller than the crop dimensions.
  """
  if not image_list:
    raise ValueError('Empty image_list.')

  # Compute the rank assertions.
  rank_assertions = []
  for i in range(len(image_list)):
    image_rank = tf.rank(image_list[i])
    rank_assert = tf.Assert(
        tf.equal(image_rank, 3),
        ['Wrong rank for tensor  %s [expected] [actual]',
         image_list[i].name, 3, image_rank])
    rank_assertions.append(rank_assert)

  with tf.control_dependencies([rank_assertions[0]]):
    image_shape = tf.shape(image_list[0])
  image_height = image_shape[0]
  image_width = image_shape[1]
  crop_size_assert = tf.Assert(
      tf.logical_and(
          tf.greater_equal(image_height, crop_height),
          tf.greater_equal(image_width, crop_width)),
      ['Crop size greater than the image size.'])

  asserts = [rank_assertions[0], crop_size_assert]

  for i in range(1, len(image_list)):
    image = image_list[i]
    asserts.append(rank_assertions[i])
    with tf.control_dependencies([rank_assertions[i]]):
      shape = tf.shape(image)
    height = shape[0]
    width = shape[1]

    height_assert = tf.Assert(
        tf.equal(height, image_height),
        ['Wrong height for tensor %s [expected][actual]',
         image.name, height, image_height])
    width_assert = tf.Assert(
        tf.equal(width, image_width),
        ['Wrong width for tensor %s [expected][actual]',
         image.name, width, image_width])
    asserts.extend([height_assert, width_assert])

  # Create a random bounding box.
  #
  # Use tf.random_uniform and not numpy.random.rand as doing the former would
  # generate random numbers at graph eval time, unlike the latter which
  # generates random numbers at graph definition time.
  with tf.control_dependencies(asserts):
    max_offset_height = tf.reshape(image_height - crop_height + 1, [])
  with tf.control_dependencies(asserts):
    max_offset_width = tf.reshape(image_width - crop_width + 1, [])
  offset_height = tf.random_uniform(
      [], maxval=max_offset_height, dtype=tf.int32)
  offset_width = tf.random_uniform(
      [], maxval=max_offset_width, dtype=tf.int32)

  return [_crop(image, offset_height, offset_width,
                crop_height, crop_width) for image in image_list]


def _central_crop(image_list, crop_height, crop_width):
  """Performs central crops of the given image list.

  Args:
    image_list: a list of image tensors of the same dimension but possibly
      varying channel.
    crop_height: the height of the image following the crop.
    crop_width: the width of the image following the crop.

  Returns:
    the list of cropped images.
  """
  outputs = []
  for image in image_list:
    image_height = tf.shape(image)[0]
    image_width = tf.shape(image)[1]

    offset_height = (image_height - crop_height) / 2
    offset_width = (image_width - crop_width) / 2

    outputs.append(_crop(image, offset_height, offset_width,
                         crop_height, crop_width))
  return outputs



def _crop(image, offset_height, offset_width, crop_height, crop_width):
  """Crops the given image using the provided offsets and sizes.

  Note that the method doesn't assume we know the input image size but it does
  assume we know the input image rank.

  Args:
    image: an image of shape [height, width, channels].
    offset_height: a scalar tensor indicating the height offset.
    offset_width: a scalar tensor indicating the width offset.
    crop_height: the height of the cropped image.
    crop_width: the width of the cropped image.

  Returns:
    the cropped (and resized) image.

  Raises:
    InvalidArgumentError: if the rank is not 3 or if the image dimensions are
      less than the crop size.
  """
  original_shape = tf.shape(image)

  rank_assertion = tf.Assert(
      tf.equal(tf.rank(image), 3),
      ['Rank of image must be equal to 3.'])
  with tf.control_dependencies([rank_assertion]):
    cropped_shape = tf.stack([crop_height, crop_width, original_shape[2]])

  size_assertion = tf.Assert(
      tf.logical_and(
          tf.greater_equal(original_shape[0], crop_height),
          tf.greater_equal(original_shape[1], crop_width)),
      ['Crop size greater than the image size.'])

  offsets = tf.to_int32(tf.stack([offset_height, offset_width, 0]))

  # Use tf.slice instead of crop_to_bounding box as it accepts tensors to
  # define the crop size.
  with tf.control_dependencies([size_assertion]):
    image = tf.slice(image, offsets, cropped_shape)
  return tf.reshape(image, cropped_shape)


def _mean_image_subtraction(image, means):
  """Subtracts the given means from each image channel.

  For example:
    means = [123.68, 116.779, 103.939]
    image = _mean_image_subtraction(image, means)

  Note that the rank of `image` must be known.

  Args:
    image: a tensor of size [height, width, C].
    means: a C-vector of values to subtract from each channel.

  Returns:
    the centered image.

  Raises:
    ValueError: If the rank of `image` is unknown, if `image` has a rank other
      than three or if the number of channels in `image` doesn't match the
      number of values in `means`.
  """
  if image.get_shape().ndims != 3:
    raise ValueError('Input must be of size [height, width, C>0]')
  num_channels = image.get_shape().as_list()[-1]
  if len(means) != num_channels:
    raise ValueError('len(means) must match the number of channels')

  channels = tf.split(axis=2, num_or_size_splits=num_channels, value=image)
  for i in range(num_channels):
    channels[i] -= means[i]
  return tf.concat(axis=2, values=channels)

第四種

#coding:utf-8
#preprocess_inception.py

"""
 Train
    step1: draw bbox on image for summary (optional)
    step2: sample_distorted_bounding_box to get distored image and distored bbox
    step3: draw distored bbox on distored image for summary (optional)
    step4: 隨機選擇一種方法對圖像進行縮放 (對於使用TensorFlow實現類似功能具有極大的參考價值)
    step5: random flip left right
    step6: 隨機選擇一種方法對顏色進行處理
    step7: subtract 0.5
    step8: multiply 2.0
 Eval
    step1: if central_fraction: central_crop
    step2: if height,width: resize bilinear
    step3: subtract 0.5
    step4: multiply 2.0
"""

import tensorflow as tf
from tensorflow.python.ops import control_flow_ops


def preprocess_image(image, label, is_training,
                     out_height=224, out_width=224,
                     bbox=None,
                     fast_mode=True,
                     add_image_summaries=True):
  """Pre-process one image for training or evaluation.

  Args:
    image: 3-D Tensor [height, width, channels] with the image. If dtype is
      tf.float32 then the range should be [0, 1], otherwise it would converted
      to tf.float32 assuming that the range is [0, MAX], where MAX is largest
      positive representable number for int(8/16/32) data type (see
      `tf.image.convert_image_dtype` for details).
    out_height: integer, image expected height.
    out_width: integer, image expected width.
    is_training: Boolean. If true it would transform an image for train,
      otherwise it would transform it for evaluation.
    bbox: 3-D float Tensor of bounding boxes arranged [1, num_boxes, coords]
      where each coordinate is [0, 1) and the coordinates are arranged as
      [ymin, xmin, ymax, xmax].
    fast_mode: Optional boolean, if True avoids slower transformations.
    add_image_summaries: Enable image summaries.

  Returns:
    3-D float Tensor containing an appropriately scaled image

  Raises:
    ValueError: if user does not provide bounding box
  """
  if is_training:
    image = preprocess_for_train(image, out_height, out_width, bbox, fast_mode,
                                 add_image_summaries=add_image_summaries)
  else:
    image = preprocess_for_eval(image, out_height, out_width)
  return image, label


def preprocess_for_train(image, out_height, out_width, bbox,
                         fast_mode=True,
                         scope=None,
                         add_image_summaries=True):
  """Distort one image for training a network.

  Distorting images provides a useful technique for augmenting the data
  set during training in order to make the network invariant to aspects
  of the image that do not effect the label.

  Additionally it would create image_summaries to display the different
  transformations applied to the image.

  Args:
    image: 3-D Tensor of image. If dtype is tf.float32 then the range should be
      [0, 1], otherwise it would converted to tf.float32 assuming that the range
      is [0, MAX], where MAX is largest positive representable number for
      int(8/16/32) data type (see `tf.image.convert_image_dtype` for details).
    out_height: integer, image expected height.
    out_width: integer, image expected width.
    bbox: 3-D float Tensor of bounding boxes arranged [1, num_boxes, coords]
      where each coordinate is [0, 1) and the coordinates are arranged
      as [ymin, xmin, ymax, xmax].
    fast_mode: Optional boolean, if True avoids slower transformations (i.e.
      bi-cubic resizing, random_hue or random_contrast).
    scope: Optional scope for name_scope.
    add_image_summaries: Enable image summaries.
  Returns:
    3-D float Tensor of distorted image used for training with range [-1, 1].
  """
  with tf.name_scope(scope, 'distort_image', [image, out_height, out_width, bbox]):
    if bbox is None:
      bbox = tf.constant([0.0, 0.0, 1.0, 1.0],
                         dtype=tf.float32,
                         shape=[1, 1, 4])
    if image.dtype != tf.float32:
      image = tf.image.convert_image_dtype(image, dtype=tf.float32)
    # Each bounding box has shape [1, num_boxes, box coords] and
    # the coordinates are ordered [ymin, xmin, ymax, xmax].
    image_with_box = tf.image.draw_bounding_boxes(tf.expand_dims(image, 0),
                                                  bbox)
    if add_image_summaries:
      tf.summary.image('image_with_bounding_boxes', image_with_box)

    distorted_image, distorted_bbox = distorted_bounding_box_crop(image, bbox)
    # Restore the shape since the dynamic slice based upon the bbox_size loses
    # the third dimension.
    distorted_image.set_shape([None, None, 3])
    image_with_distorted_box = tf.image.draw_bounding_boxes(
        tf.expand_dims(image, 0), distorted_bbox)
    if add_image_summaries:
      tf.summary.image('images_with_distorted_bounding_box',
                       image_with_distorted_box)

    # This resizing operation may distort the images because the aspect
    # ratio is not respected. We select a resize method in a round robin
    # fashion based on the thread number.
    # Note that ResizeMethod contains 4 enumerated resizing methods.

    # We select only 1 case for fast_mode bilinear.
    num_resize_cases = 1 if fast_mode else 4
    distorted_image = apply_with_random_selector( # 隨機挑選一種方法，來進行圖像尺寸的變換
        distorted_image,
        lambda x, method: tf.image.resize_images(x, [out_height, out_width], method), # 關於用數字來指定resize方法，可以參考tensorflow/python/ops/image_ops_impl.py的第934行
        num_cases=num_resize_cases)

    if add_image_summaries:
      tf.summary.image('cropped_resized_image',
                       tf.expand_dims(distorted_image, 0))

    # Randomly flip the image horizontally.
    distorted_image = tf.image.random_flip_left_right(distorted_image)

    # Randomly distort the colors. There are 1 or 4 ways to do it.
    num_distort_cases = 1 if fast_mode else 4
    distorted_image = apply_with_random_selector( # 隨機挑選一種方法，來進行圖像顏色相關的變換
        distorted_image,
        lambda x, ordering: distort_color(x, ordering, fast_mode),
        num_cases=num_distort_cases)

    if add_image_summaries:
      tf.summary.image('final_distorted_image',
                       tf.expand_dims(distorted_image, 0))
    distorted_image = tf.subtract(distorted_image, 0.5)
    distorted_image = tf.multiply(distorted_image, 2.0)
    return distorted_image


def preprocess_for_eval(image, out_height, out_width,
                        central_fraction=0.875, scope=None):
  """Prepare one image for evaluation.

  If height and width are specified it would output an image with that size by
  applying resize_bilinear.

  If central_fraction is specified it would crop the central fraction of the
  input image.

  Args:
    image: 3-D Tensor of image. If dtype is tf.float32 then the range should be
      [0, 1], otherwise it would converted to tf.float32 assuming that the range
      is [0, MAX], where MAX is largest positive representable number for
      int(8/16/32) data type (see `tf.image.convert_image_dtype` for details).
    out_height: integer, image expected height.
    out_width: integer, image expected width.
    central_fraction: Optional Float, fraction of the image to crop.
    scope: Optional scope for name_scope.
  Returns:
    3-D float Tensor of prepared image.
  """
  with tf.name_scope(scope, 'eval_image', [image, out_height, out_width]):
    if image.dtype != tf.float32:
      image = tf.image.convert_image_dtype(image, dtype=tf.float32)
    # Crop the central region of the image with an area containing 87.5% of
    # the original image.
    if central_fraction:
      image = tf.image.central_crop(image, central_fraction=central_fraction)

    if out_height and out_width:
      # Resize the image to the specified height and width.
      image = tf.expand_dims(image, 0)
      image = tf.image.resize_bilinear(image, [out_height, out_width],
                                       align_corners=False)
      image = tf.squeeze(image, [0])
    image = tf.subtract(image, 0.5)
    image = tf.multiply(image, 2.0)
    return image


def distorted_bounding_box_crop(image,
                                bbox,
                                min_object_covered=0.1,
                                aspect_ratio_range=(0.75, 1.33),
                                area_range=(0.05, 1.0),
                                max_attempts=100,
                                scope=None):
  """Generates cropped_image using a one of the bboxes randomly distorted.

  See `tf.image.sample_distorted_bounding_box` for more documentation.

  Args:
    image: 3-D Tensor of image (it will be converted to floats in [0, 1]).
    bbox: 3-D float Tensor of bounding boxes arranged [1, num_boxes, coords]
      where each coordinate is [0, 1) and the coordinates are arranged
      as [ymin, xmin, ymax, xmax]. If num_boxes is 0 then it would use the whole
      image.
    min_object_covered: An optional `float`. Defaults to `0.1`. The cropped
      area of the image must contain at least this fraction of any bounding box
      supplied.
    aspect_ratio_range: An optional list of `floats`. The cropped area of the
      image must have an aspect ratio = width / height within this range.
    area_range: An optional list of `floats`. The cropped area of the image
      must contain a fraction of the supplied image within in this range.
    max_attempts: An optional `int`. Number of attempts at generating a cropped
      region of the image of the specified constraints. After `max_attempts`
      failures, return the entire image.
    scope: Optional scope for name_scope.
  Returns:
    A tuple, a 3-D Tensor cropped_image and the distorted bbox
  """
  with tf.name_scope(scope, 'distorted_bounding_box_crop', [image, bbox]):
    # Each bounding box has shape [1, num_boxes, box coords] and
    # the coordinates are ordered [ymin, xmin, ymax, xmax].

    # A large fraction of image datasets contain a human-annotated bounding
    # box delineating the region of the image containing the object of interest.
    # We choose to create a new bounding box for the object which is a randomly
    # distorted version of the human-annotated bounding box that obeys an
    # allowed range of aspect ratios, sizes and overlap with the human-annotated
    # bounding box. If no box is supplied, then we assume the bounding box is
    # the entire image.
    sample_distorted_bounding_box = tf.image.sample_distorted_bounding_box(
        tf.shape(image),
        bounding_boxes=bbox,
        min_object_covered=min_object_covered,
        aspect_ratio_range=aspect_ratio_range,
        area_range=area_range,
        max_attempts=max_attempts,
        use_image_if_no_bounding_boxes=True)
    bbox_begin, bbox_size, distort_bbox = sample_distorted_bounding_box

    # Crop the image to the specified bounding box.
    cropped_image = tf.slice(image, bbox_begin, bbox_size)
    return cropped_image, distort_bbox


def apply_with_random_selector(x, func, num_cases):
  """Computes func(x, sel), with sel sampled from [0...num_cases-1].

  Args:
    x: input Tensor.
    func: Python function to apply.
    num_cases: Python int32, number of cases to sample sel from.

  Returns:
    The result of func(x, sel), where func receives the value of the
    selector as a python integer, but sel is sampled dynamically.
  """
  sel = tf.random_uniform([], maxval=num_cases, dtype=tf.int32)
  # Pass the real x only to one of the func calls.
  return control_flow_ops.merge([
      func(control_flow_ops.switch(x, tf.equal(sel, case))[1], case)
      for case in range(num_cases)])[0]


def distort_color(image, color_ordering=0, fast_mode=True, scope=None):
  """Distort the color of a Tensor image.

  Each color distortion is non-commutative and thus ordering of the color ops
  matters. Ideally we would randomly permute the ordering of the color ops.
  Rather then adding that level of complication, we select a distinct ordering
  of color ops for each preprocessing thread.

  Args:
    image: 3-D Tensor containing single image in [0, 1].
    color_ordering: Python int, a type of distortion (valid values: 0-3).
    fast_mode: Avoids slower ops (random_hue and random_contrast)
    scope: Optional scope for name_scope.
  Returns:
    3-D Tensor color-distorted image on range [0, 1]
  Raises:
    ValueError: if color_ordering not in [0, 3]
  """
  with tf.name_scope(scope, 'distort_color', [image]):
    if fast_mode:
      if color_ordering == 0:
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
      else:
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
    else:
      if color_ordering == 0:
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
        image = tf.image.random_hue(image, max_delta=0.2)
        image = tf.image.random_contrast(image, lower=0.5, upper=1.5)
      elif color_ordering == 1:
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
        image = tf.image.random_contrast(image, lower=0.5, upper=1.5)
        image = tf.image.random_hue(image, max_delta=0.2)
      elif color_ordering == 2:
        image = tf.image.random_contrast(image, lower=0.5, upper=1.5)
        image = tf.image.random_hue(image, max_delta=0.2)
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
      elif color_ordering == 3:
        image = tf.image.random_hue(image, max_delta=0.2)
        image = tf.image.random_saturation(image, lower=0.5, upper=1.5)
        image = tf.image.random_contrast(image, lower=0.5, upper=1.5)
        image = tf.image.random_brightness(image, max_delta=32. / 255.)
      else:
        raise ValueError('color_ordering must be in [0, 3]')

    # The random_* ops do not necessarily clamp.
    return tf.clip_by_value(image, 0.0, 1.0)

注意：歡迎大家轉載，但需註明出處哦
$\quad$$\quad$$\;$https://blog.csdn.net/u014061630/article/details/83859162