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# -*- coding: utf-8 -*-
"""Normalization layers.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from ..engine.base_layer import Layer, InputSpec
from .. import initializers
from .. import regularizers
from .. import constraints
from .. import backend as K
from ..legacy import interfaces
class BatchNormalization(Layer):
"""Batch normalization layer (Ioffe and Szegedy, 2014).
Normalize the activations of the previous layer at each batch,
i.e. applies a transformation that maintains the mean activation
close to 0 and the activation standard deviation close to 1.
# Arguments
axis: Integer, the axis that should be normalized
(typically the features axis).
For instance, after a `Conv2D` layer with
`data_format="channels_first"`,
set `axis=1` in `BatchNormalization`.
momentum: Momentum for the moving mean and the moving variance.
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
will 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: Optional constraint for the beta weight.
gamma_constraint: Optional constraint for the gamma weight.
# Input shape
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
# Output shape
Same shape as input.
# References
- [Batch Normalization: Accelerating Deep Network Training by
Reducing Internal Covariate Shift](https://arxiv.org/abs/1502.03167)
"""
@interfaces.legacy_batchnorm_support
def __init__(self,
axis=-1,
momentum=0.99,
epsilon=1e-3,
center=True,
scale=True,
beta_initializer='zeros',
gamma_initializer='ones',
moving_mean_initializer='zeros',
moving_variance_initializer='ones',
beta_regularizer=None,
gamma_regularizer=None,
beta_constraint=None,
gamma_constraint=None,
**kwargs):
super(BatchNormalization, self).__init__(**kwargs)
self.supports_masking = True
self.axis = axis
self.momentum = momentum
self.epsilon = epsilon
self.center = center
self.scale = scale
self.beta_initializer = initializers.get(beta_initializer)
self.gamma_initializer = initializers.get(gamma_initializer)
self.moving_mean_initializer = initializers.get(moving_mean_initializer)
self.moving_variance_initializer = (
initializers.get(moving_variance_initializer))
self.beta_regularizer = regularizers.get(beta_regularizer)
self.gamma_regularizer = regularizers.get(gamma_regularizer)
self.beta_constraint = constraints.get(beta_constraint)
self.gamma_constraint = constraints.get(gamma_constraint)
def build(self, input_shape):
dim = input_shape[self.axis]
if dim is None:
raise ValueError('Axis ' + str(self.axis) + ' of '
'input tensor should have a defined dimension '
'but the layer received an input with shape ' +
str(input_shape) + '.')
self.input_spec = InputSpec(ndim=len(input_shape),
axes={self.axis: dim})
shape = (dim,)
if self.scale:
self.gamma = self.add_weight(shape=shape,
name='gamma',
initializer=self.gamma_initializer,
regularizer=self.gamma_regularizer,
constraint=self.gamma_constraint)
else:
self.gamma = None
if self.center:
self.beta = self.add_weight(shape=shape,
name='beta',
initializer=self.beta_initializer,
regularizer=self.beta_regularizer,
constraint=self.beta_constraint)
else:
self.beta = None
self.moving_mean = self.add_weight(
shape=shape,
name='moving_mean',
initializer=self.moving_mean_initializer,
trainable=False)
self.moving_variance = self.add_weight(
shape=shape,
name='moving_variance',
initializer=self.moving_variance_initializer,
trainable=False)
self.built = True
def call(self, inputs, training=None):
input_shape = K.int_shape(inputs)
# Prepare broadcasting shape.
ndim = len(input_shape)
reduction_axes = list(range(len(input_shape)))
del reduction_axes[self.axis]
broadcast_shape = [1] * len(input_shape)
broadcast_shape[self.axis] = input_shape[self.axis]
# Determines whether broadcasting is needed.
needs_broadcasting = (sorted(reduction_axes) != list(range(ndim))[:-1])
def normalize_inference():
if needs_broadcasting:
# In this case we must explicitly broadcast all parameters.
broadcast_moving_mean = K.reshape(self.moving_mean,
broadcast_shape)
broadcast_moving_variance = K.reshape(self.moving_variance,
broadcast_shape)
if self.center:
broadcast_beta = K.reshape(self.beta, broadcast_shape)
else:
broadcast_beta = None
if self.scale:
broadcast_gamma = K.reshape(self.gamma,
broadcast_shape)
else:
broadcast_gamma = None
return K.batch_normalization(
inputs,
broadcast_moving_mean,
broadcast_moving_variance,
broadcast_beta,
broadcast_gamma,
axis=self.axis,
epsilon=self.epsilon)
else:
return K.batch_normalization(
inputs,
self.moving_mean,
self.moving_variance,
self.beta,
self.gamma,
axis=self.axis,
epsilon=self.epsilon)
# If the learning phase is *static* and set to inference:
if training in {0, False}:
return normalize_inference()
# If the learning is either dynamic, or set to training:
normed_training, mean, variance = K.normalize_batch_in_training(
inputs, self.gamma, self.beta, reduction_axes,
epsilon=self.epsilon)
if K.backend() != 'cntk':
sample_size = K.prod([K.shape(inputs)[axis]
for axis in reduction_axes])
sample_size = K.cast(sample_size, dtype=K.dtype(inputs))
if K.backend() == 'tensorflow' and sample_size.dtype != 'float32':
sample_size = K.cast(sample_size, dtype='float32')
# sample variance - unbiased estimator of population variance
variance *= sample_size / (sample_size - (1.0 + self.epsilon))
self.add_update([K.moving_average_update(self.moving_mean,
mean,
self.momentum),
K.moving_average_update(self.moving_variance,
variance,
self.momentum)],
inputs)
# Pick the normalized form corresponding to the training phase.
return K.in_train_phase(normed_training,
normalize_inference,
training=training)
def get_config(self):
config = {
'axis': self.axis,
'momentum': self.momentum,
'epsilon': self.epsilon,
'center': self.center,
'scale': self.scale,
'beta_initializer': initializers.serialize(self.beta_initializer),
'gamma_initializer': initializers.serialize(self.gamma_initializer),
'moving_mean_initializer':
initializers.serialize(self.moving_mean_initializer),
'moving_variance_initializer':
initializers.serialize(self.moving_variance_initializer),
'beta_regularizer': regularizers.serialize(self.beta_regularizer),
'gamma_regularizer': regularizers.serialize(self.gamma_regularizer),
'beta_constraint': constraints.serialize(self.beta_constraint),
'gamma_constraint': constraints.serialize(self.gamma_constraint)
}
base_config = super(BatchNormalization, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
def compute_output_shape(self, input_shape):
return input_shape