#! /usr/bin/python
# -*- coding: utf-8 -*-
import numpy as np
import tensorflow as tf
__all__ = [
'Initializer', 'Zeros', 'Ones', 'Constant', 'RandomUniform', 'RandomNormal', 'TruncatedNormal',
'deconv2d_bilinear_upsampling_initializer'
]
[docs]class Initializer(object):
"""Initializer base class: all initializers inherit from this class.
"""
def __call__(self, shape, dtype=None):
"""Returns a tensor object initialized as specified by the initializer.
Parameters
----------
shape : tuple of int.
The shape of the tensor.
dtype : Optional dtype of the tensor.
If not provided will return tensor of `tf.float32`.
Returns
-------
"""
raise NotImplementedError
def get_config(self):
"""Returns the configuration of the initializer as a JSON-serializable dict.
Returns
-------
A JSON-serializable Python dict.
"""
return {}
@classmethod
def from_config(cls, config):
"""Instantiates an initializer from a configuration dictionary.
Parameters
----------
config : A python dictionary.
It will typically be the output of `get_config`.
Returns
-------
An Initializer instance.
"""
if 'dtype' in config:
config.pop('dtype')
return cls(**config)
[docs]class Zeros(Initializer):
"""Initializer that generates tensors initialized to 0.
"""
def __call__(self, shape, dtype=tf.float32):
return tf.zeros(shape, dtype=dtype)
[docs]class Ones(Initializer):
"""Initializer that generates tensors initialized to 1.
"""
def __call__(self, shape, dtype=tf.float32):
return tf.ones(shape, dtype=dtype)
[docs]class Constant(Initializer):
"""Initializer that generates tensors initialized to a constant value.
Parameters
----------
value : A python scalar or a numpy array.
The assigned value.
"""
def __init__(self, value=0):
self.value = value
def __call__(self, shape, dtype=None):
return tf.constant(self.value, shape=shape, dtype=dtype)
def get_config(self):
return {"value": self.value}
[docs]class RandomNormal(Initializer):
"""Initializer that generates tensors with a normal distribution.
Parameters
----------
mean : A python scalar or a scalar tensor.
Mean of the random values to generate.
stddev : A python scalar or a scalar tensor.
Standard deviation of the random values to generate.
seed : A Python integer.
Used to seed the random generator.
"""
def __init__(self, mean=0.0, stddev=0.05, seed=None):
self.mean = mean
self.stddev = stddev
self.seed = seed
def __call__(self, shape, dtype=tf.float32):
return tf.random.normal(shape, self.mean, self.stddev, dtype=dtype, seed=self.seed)
def get_config(self):
return {"mean": self.mean, "stddev": self.stddev, "seed": self.seed}
[docs]class TruncatedNormal(Initializer):
"""Initializer that generates a truncated normal distribution.
These values are similar to values from a `RandomNormal`
except that values more than two standard deviations from the mean
are discarded and re-drawn. This is the recommended initializer for
neural network weights and filters.
Parameters
----------
mean : A python scalar or a scalar tensor.
Mean of the random values to generate.
stddev : A python scalar or a scalar tensor.
Standard deviation of the andom values to generate.
seed : A Python integer.
Used to seed the random generator.
"""
def __init__(self, mean=0.0, stddev=0.05, seed=None):
self.mean = mean
self.stddev = stddev
self.seed = seed
def __call__(self, shape, dtype=tf.float32):
return tf.random.truncated_normal(shape, self.mean, self.stddev, dtype=dtype, seed=self.seed)
def get_config(self):
return {"mean": self.mean, "stddev": self.stddev, "seed": self.seed}
[docs]def deconv2d_bilinear_upsampling_initializer(shape):
"""Returns the initializer that can be passed to DeConv2dLayer for initializing the
weights in correspondence to channel-wise bilinear up-sampling.
Used in segmentation approaches such as [FCN](https://arxiv.org/abs/1605.06211)
Parameters
----------
shape : tuple of int
The shape of the filters, [height, width, output_channels, in_channels].
It must match the shape passed to DeConv2dLayer.
Returns
-------
``tf.constant_initializer``
A constant initializer with weights set to correspond to per channel bilinear upsampling
when passed as W_int in DeConv2dLayer
"""
if shape[0] != shape[1]:
raise Exception('deconv2d_bilinear_upsampling_initializer only supports symmetrical filter sizes')
if shape[3] < shape[2]:
raise Exception(
'deconv2d_bilinear_upsampling_initializer behaviour is not defined for num_in_channels < num_out_channels '
)
filter_size = shape[0]
num_out_channels = shape[2]
num_in_channels = shape[3]
# Create bilinear filter kernel as numpy array
bilinear_kernel = np.zeros([filter_size, filter_size], dtype=np.float32)
scale_factor = (filter_size + 1) // 2
if filter_size % 2 == 1:
center = scale_factor - 1
else:
center = scale_factor - 0.5
for x in range(filter_size):
for y in range(filter_size):
bilinear_kernel[x, y] = (1 - abs(x - center) / scale_factor) * (1 - abs(y - center) / scale_factor)
weights = np.zeros((filter_size, filter_size, num_out_channels, num_in_channels), dtype=np.float32)
for i in range(num_out_channels):
weights[:, :, i, i] = bilinear_kernel
# assign numpy array to constant_initalizer and pass to get_variable
return tf.constant_initializer(value=weights)
# Alias
zeros = Zeros
ones = Ones
constant = Constant
random_uniform = RandomUniform
random_normal = RandomNormal
truncated_normal = TruncatedNormal