normalization.py

# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
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# you may not use this file except in compliance with the License.
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#     http://www.apache.org/licenses/LICENSE-2.0
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# =============================================================================

"""Contains the normalization layer classes and their functional aliases.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function


from tensorflow.python.keras import layers as keras_layers
from tensorflow.python.layers import base
from tensorflow.python.ops import init_ops
from tensorflow.python.util.tf_export import tf_export


@tf_export('layers.BatchNormalization')
class BatchNormalization(keras_layers.BatchNormalization, base.Layer):
  """Batch Normalization layer from http://arxiv.org/abs/1502.03167.

  "Batch Normalization: Accelerating Deep Network Training by Reducing
  Internal Covariate Shift"

  Sergey Ioffe, Christian Szegedy

  Arguments:
    axis: An `int` or list of `int`, the axis or axes that should be
        normalized, typically the features axis/axes. For instance, after a
        `Conv2D` layer with `data_format="channels_first"`, set `axis=1`. If a
        list of axes is provided, each axis in `axis` will be normalized
        simultaneously. Default is `-1` which uses the last axis. Note: when
        using multi-axis batch norm, the `beta`, `gamma`, `moving_mean`, and
        `moving_variance` variables are the same rank as the input Tensor, with
        dimension size 1 in all reduced (non-axis) dimensions).
    momentum: Momentum for the moving average.
    epsilon: Small float added to variance to avoid dividing by zero.
    center: If True, add offset of `beta` to normalized tensor. If False, `beta`
      is ignored.
    scale: If True, multiply by `gamma`. If False, `gamma` is
      not used. When the next layer is linear (also e.g. `nn.relu`), this can be
      disabled since the scaling can be done by the next layer.
    beta_initializer: Initializer for the beta weight.
    gamma_initializer: Initializer for the gamma weight.
    moving_mean_initializer: Initializer for the moving mean.
    moving_variance_initializer: Initializer for the moving variance.
    beta_regularizer: Optional regularizer for the beta weight.
    gamma_regularizer: Optional regularizer for the gamma weight.
    beta_constraint: An optional projection function to be applied to the `beta`
        weight after being updated by an `Optimizer` (e.g. used to implement
        norm constraints or value constraints for layer weights). The function
        must take as input the unprojected variable and must return the
        projected variable (which must have the same shape). Constraints are
        not safe to use when doing asynchronous distributed training.
    gamma_constraint: An optional projection function to be applied to the
        `gamma` weight after being updated by an `Optimizer`.
    renorm: Whether to use Batch Renormalization
      (https://arxiv.org/abs/1702.03275). This adds extra variables during
      training. The inference is the same for either value of this parameter.
    renorm_clipping: A dictionary that may map keys 'rmax', 'rmin', 'dmax' to
      scalar `Tensors` used to clip the renorm correction. The correction
      `(r, d)` is used as `corrected_value = normalized_value * r + d`, with
      `r` clipped to [rmin, rmax], and `d` to [-dmax, dmax]. Missing rmax, rmin,
      dmax are set to inf, 0, inf, respectively.
    renorm_momentum: Momentum used to update the moving means and standard
      deviations with renorm. Unlike `momentum`, this affects training
      and should be neither too small (which would add noise) nor too large
      (which would give stale estimates). Note that `momentum` is still applied
      to get the means and variances for inference.
    fused: if `None` or `True`, use a faster, fused implementation if possible.
      If `False`, use the system recommended implementation.
    trainable: Boolean, if `True` also add variables to the graph collection
      `GraphKeys.TRAINABLE_VARIABLES` (see tf.Variable).
    virtual_batch_size: An `int`. By default, `virtual_batch_size` is `None`,
      which means batch normalization is performed across the whole batch. When
      `virtual_batch_size` is not `None`, instead perform "Ghost Batch
      Normalization", which creates virtual sub-batches which are each
      normalized separately (with shared gamma, beta, and moving statistics).
      Must divide the actual batch size during execution.
    adjustment: A function taking the `Tensor` containing the (dynamic) shape of
      the input tensor and returning a pair (scale, bias) to apply to the
      normalized values (before gamma and beta), only during training. For
      example, if axis==-1,
        `adjustment = lambda shape: (
          tf.random_uniform(shape[-1:], 0.93, 1.07),
          tf.random_uniform(shape[-1:], -0.1, 0.1))`
      will scale the normalized value by up to 7% up or down, then shift the
      result by up to 0.1 (with independent scaling and bias for each feature
      but shared across all examples), and finally apply gamma and/or beta. If
      `None`, no adjustment is applied. Cannot be specified if
      virtual_batch_size is specified.
    name: A string, the name of the layer.
  """

  def __init__(self,
               axis=-1,
               momentum=0.99,
               epsilon=1e-3,
               center=True,
               scale=True,
               beta_initializer=init_ops.zeros_initializer(),
               gamma_initializer=init_ops.ones_initializer(),
               moving_mean_initializer=init_ops.zeros_initializer(),
               moving_variance_initializer=init_ops.ones_initializer(),
               beta_regularizer=None,
               gamma_regularizer=None,
               beta_constraint=None,
               gamma_constraint=None,
               renorm=False,
               renorm_clipping=None,
               renorm_momentum=0.99,
               fused=None,
               trainable=True,
               virtual_batch_size=None,
               adjustment=None,
               name=None,
               **kwargs):
    super(BatchNormalization, self).__init__(
        axis=axis,
        momentum=momentum,
        epsilon=epsilon,
        center=center,
        scale=scale,
        beta_initializer=beta_initializer,
        gamma_initializer=gamma_initializer,
        moving_mean_initializer=moving_mean_initializer,
        moving_variance_initializer=moving_variance_initializer,
        beta_regularizer=beta_regularizer,
        gamma_regularizer=gamma_regularizer,
        beta_constraint=beta_constraint,
        gamma_constraint=gamma_constraint,
        renorm=renorm,
        renorm_clipping=renorm_clipping,
        renorm_momentum=renorm_momentum,
        fused=fused,
        trainable=trainable,
        virtual_batch_size=virtual_batch_size,
        adjustment=adjustment,
        name=name,
        **kwargs)

  def call(self, inputs, training=False):
    return super(BatchNormalization, self).call(inputs, training=training)


@tf_export('layers.batch_normalization')
def batch_normalization(inputs,
                        axis=-1,
                        momentum=0.99,
                        epsilon=1e-3,
                        center=True,
                        scale=True,
                        beta_initializer=init_ops.zeros_initializer(),
                        gamma_initializer=init_ops.ones_initializer(),
                        moving_mean_initializer=init_ops.zeros_initializer(),
                        moving_variance_initializer=init_ops.ones_initializer(),
                        beta_regularizer=None,
                        gamma_regularizer=None,
                        beta_constraint=None,
                        gamma_constraint=None,
                        training=False,
                        trainable=True,
                        name=None,
                        reuse=None,
                        renorm=False,
                        renorm_clipping=None,
                        renorm_momentum=0.99,
                        fused=None,
                        virtual_batch_size=None,
                        adjustment=None):
  """Functional interface for the batch normalization layer.

  Reference: http://arxiv.org/abs/1502.03167

  "Batch Normalization: Accelerating Deep Network Training by Reducing
  Internal Covariate Shift"

  Sergey Ioffe, Christian Szegedy

  Note: when training, the moving_mean and moving_variance need to be updated.
  By default the update ops are placed in `tf.GraphKeys.UPDATE_OPS`, so they
  need to be added as a dependency to the `train_op`. Also, be sure to add
  any batch_normalization ops before getting the update_ops collection.
  Otherwise, update_ops will be empty, and training/inference will not work
  properly. For example:

  ```python
    x_norm = tf.layers.batch_normalization(x, training=training)

    # ...

    update_ops = tf.get_collection(tf.GraphKeys.UPDATE_OPS)
    with tf.control_dependencies(update_ops):
      train_op = optimizer.minimize(loss)
  ```

  Arguments:
    inputs: Tensor input.
    axis: An `int`, the axis that should be normalized (typically the features
      axis). For instance, after a `Convolution2D` layer with
      `data_format="channels_first"`, set `axis=1` in `BatchNormalization`.
    momentum: Momentum for the moving average.
    epsilon: Small float added to variance to avoid dividing by zero.
    center: If True, add offset of `beta` to normalized tensor. If False, `beta`
      is ignored.
    scale: If True, multiply by `gamma`. If False, `gamma` is
      not used. When the next layer is linear (also e.g. `nn.relu`), this can be
      disabled since the scaling can be done by the next layer.
    beta_initializer: Initializer for the beta weight.
    gamma_initializer: Initializer for the gamma weight.
    moving_mean_initializer: Initializer for the moving mean.
    moving_variance_initializer: Initializer for the moving variance.
    beta_regularizer: Optional regularizer for the beta weight.
    gamma_regularizer: Optional regularizer for the gamma weight.
    beta_constraint: An optional projection function to be applied to the `beta`
        weight after being updated by an `Optimizer` (e.g. used to implement
        norm constraints or value constraints for layer weights). The function
        must take as input the unprojected variable and must return the
        projected variable (which must have the same shape). Constraints are
        not safe to use when doing asynchronous distributed training.
    gamma_constraint: An optional projection function to be applied to the
        `gamma` weight after being updated by an `Optimizer`.
    training: Either a Python boolean, or a TensorFlow boolean scalar tensor
      (e.g. a placeholder). Whether to return the output in training mode
      (normalized with statistics of the current batch) or in inference mode
      (normalized with moving statistics). **NOTE**: make sure to set this
      parameter correctly, or else your training/inference will not work
      properly.
    trainable: Boolean, if `True` also add variables to the graph collection
      `GraphKeys.TRAINABLE_VARIABLES` (see tf.Variable).
    name: String, the name of the layer.
    reuse: Boolean, whether to reuse the weights of a previous layer
      by the same name.
    renorm: Whether to use Batch Renormalization
      (https://arxiv.org/abs/1702.03275). This adds extra variables during
      training. The inference is the same for either value of this parameter.
    renorm_clipping: A dictionary that may map keys 'rmax', 'rmin', 'dmax' to
      scalar `Tensors` used to clip the renorm correction. The correction
      `(r, d)` is used as `corrected_value = normalized_value * r + d`, with
      `r` clipped to [rmin, rmax], and `d` to [-dmax, dmax]. Missing rmax, rmin,
      dmax are set to inf, 0, inf, respectively.
    renorm_momentum: Momentum used to update the moving means and standard
      deviations with renorm. Unlike `momentum`, this affects training
      and should be neither too small (which would add noise) nor too large
      (which would give stale estimates). Note that `momentum` is still applied
      to get the means and variances for inference.
    fused: if `None` or `True`, use a faster, fused implementation if possible.
      If `False`, use the system recommended implementation.
    virtual_batch_size: An `int`. By default, `virtual_batch_size` is `None`,
      which means batch normalization is performed across the whole batch. When
      `virtual_batch_size` is not `None`, instead perform "Ghost Batch
      Normalization", which creates virtual sub-batches which are each
      normalized separately (with shared gamma, beta, and moving statistics).
      Must divide the actual batch size during execution.
    adjustment: A function taking the `Tensor` containing the (dynamic) shape of
      the input tensor and returning a pair (scale, bias) to apply to the
      normalized values (before gamma and beta), only during training. For
      example, if axis==-1,
        `adjustment = lambda shape: (
          tf.random_uniform(shape[-1:], 0.93, 1.07),
          tf.random_uniform(shape[-1:], -0.1, 0.1))`
      will scale the normalized value by up to 7% up or down, then shift the
      result by up to 0.1 (with independent scaling and bias for each feature
      but shared across all examples), and finally apply gamma and/or beta. If
      `None`, no adjustment is applied. Cannot be specified if
      virtual_batch_size is specified.

  Returns:
    Output tensor.

  Raises:
    ValueError: if eager execution is enabled.
  """
  layer = BatchNormalization(
      axis=axis,
      momentum=momentum,
      epsilon=epsilon,
      center=center,
      scale=scale,
      beta_initializer=beta_initializer,
      gamma_initializer=gamma_initializer,
      moving_mean_initializer=moving_mean_initializer,
      moving_variance_initializer=moving_variance_initializer,
      beta_regularizer=beta_regularizer,
      gamma_regularizer=gamma_regularizer,
      beta_constraint=beta_constraint,
      gamma_constraint=gamma_constraint,
      renorm=renorm,
      renorm_clipping=renorm_clipping,
      renorm_momentum=renorm_momentum,
      fused=fused,
      trainable=trainable,
      virtual_batch_size=virtual_batch_size,
      adjustment=adjustment,
      name=name,
      _reuse=reuse,
      _scope=name)
  return layer.apply(inputs, training=training)


# Aliases

BatchNorm = BatchNormalization
batch_norm = batch_normalization