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from keras.engine import Layer, InputSpec
from keras import initializers, regularizers, constraints
from keras import backend as K
from keras.utils.generic_utils import get_custom_objects
import tensorflow as tf
class InstanceNormalization(Layer):
"""Instance normalization layer (Lei Ba et al, 2016, Ulyanov et al., 2016).
Normalize the activations of the previous layer at each step,
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 `InstanceNormalization`.
Setting `axis=None` will normalize all values in each instance of the batch.
Axis 0 is the batch dimension. `axis` cannot be set to 0 to avoid errors.
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.
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
- [Layer Normalization](https://arxiv.org/abs/1607.06450)
- [Instance Normalization: The Missing Ingredient for Fast Stylization](https://arxiv.org/abs/1607.08022)
"""
def __init__(self,
axis=None,
epsilon=1e-3,
center=True,
scale=True,
beta_initializer='zeros',
gamma_initializer='ones',
beta_regularizer=None,
gamma_regularizer=None,
beta_constraint=None,
gamma_constraint=None,
**kwargs):
super(InstanceNormalization, self).__init__(**kwargs)
self.supports_masking = True
self.axis = axis
self.epsilon = epsilon
self.center = center
self.scale = scale
self.beta_initializer = initializers.get(beta_initializer)
self.gamma_initializer = initializers.get(gamma_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):
ndim = len(input_shape)
if self.axis == 0:
raise ValueError('Axis cannot be zero')
if (self.axis is not None) and (ndim == 2):
raise ValueError('Cannot specify axis for rank 1 tensor')
self.input_spec = InputSpec(ndim=ndim)
if self.axis is None:
shape = (1,)
else:
shape = (input_shape[self.axis],)
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.built = True
def call(self, inputs, training=None):
input_shape = K.int_shape(inputs)
reduction_axes = list(range(0, len(input_shape)))
if (self.axis is not None):
del reduction_axes[self.axis]
del reduction_axes[0]
mean, var = tf.nn.moments(inputs, reduction_axes, keep_dims=True)
stddev = tf.sqrt(var) + self.epsilon
normed = (inputs - mean) / stddev
broadcast_shape = [1] * len(input_shape)
if self.axis is not None:
broadcast_shape[self.axis] = input_shape[self.axis]
if self.scale:
broadcast_gamma = K.reshape(self.gamma, broadcast_shape)
normed = normed * broadcast_gamma
if self.center:
broadcast_beta = K.reshape(self.beta, broadcast_shape)
normed = normed + broadcast_beta
return normed
def get_config(self):
config = {
'axis': self.axis,
'epsilon': self.epsilon,
'center': self.center,
'scale': self.scale,
'beta_initializer': initializers.serialize(self.beta_initializer),
'gamma_initializer': initializers.serialize(self.gamma_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(InstanceNormalization, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
get_custom_objects().update({'InstanceNormalization': InstanceNormalization})
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