# Copyright 2016 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Contains convenience wrappers for various Neural Network TensorFlow losses.
All the losses defined here add themselves to the LOSSES_COLLECTION
collection.
l1_loss: Define a L1 Loss, useful for regularization, i.e. lasso.
l2_loss: Define a L2 Loss, useful for regularization, i.e. weight decay.
cross_entropy_loss: Define a cross entropy loss using
softmax_cross_entropy_with_logits. Useful for classification.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import tensorflow as tf
# In order to gather all losses in a network, the user should use this
# key for get_collection, i.e:
# losses = tf.get_collection(slim.losses.LOSSES_COLLECTION)
LOSSES_COLLECTION = '_losses'
def l1_regularizer(weight=1.0, scope=None):
"""Define a L1 regularizer.
Args:
weight: scale the loss by this factor.
scope: Optional scope for op_scope.
Returns:
a regularizer function.
"""
def regularizer(tensor):
with tf.op_scope([tensor], scope, 'L1Regularizer'):
l1_weight = tf.convert_to_tensor(weight,
dtype=tensor.dtype.base_dtype,
name='weight')
return tf.mul(l1_weight, tf.reduce_sum(tf.abs(tensor)), name='value')
return regularizer
def l2_regularizer(weight=1.0, scope=None):
"""Define a L2 regularizer.
Args:
weight: scale the loss by this factor.
scope: Optional scope for op_scope.
Returns:
a regularizer function.
"""
def regularizer(tensor):
with tf.op_scope([tensor], scope, 'L2Regularizer'):
l2_weight = tf.convert_to_tensor(weight,
dtype=tensor.dtype.base_dtype,
name='weight')
return tf.mul(l2_weight, tf.nn.l2_loss(tensor), name='value')
return regularizer
def l1_l2_regularizer(weight_l1=1.0, weight_l2=1.0, scope=None):
"""Define a L1L2 regularizer.
Args:
weight_l1: scale the L1 loss by this factor.
weight_l2: scale the L2 loss by this factor.
scope: Optional scope for op_scope.
Returns:
a regularizer function.
"""
def regularizer(tensor):
with tf.op_scope([tensor], scope, 'L1L2Regularizer'):
weight_l1_t = tf.convert_to_tensor(weight_l1,
dtype=tensor.dtype.base_dtype,
name='weight_l1')
weight_l2_t = tf.convert_to_tensor(weight_l2,
dtype=tensor.dtype.base_dtype,
name='weight_l2')
reg_l1 = tf.mul(weight_l1_t, tf.reduce_sum(tf.abs(tensor)),
name='value_l1')
reg_l2 = tf.mul(weight_l2_t, tf.nn.l2_loss(tensor),
name='value_l2')
return tf.add(reg_l1, reg_l2, name='value')
return regularizer
def l1_loss(tensor, weight=1.0, scope=None):
"""Define a L1Loss, useful for regularize, i.e. lasso.
Args:
tensor: tensor to regularize.
weight: scale the loss by this factor.
scope: Optional scope for op_scope.
Returns:
the L1 loss op.
"""
with tf.op_scope([tensor], scope, 'L1Loss'):
weight = tf.convert_to_tensor(weight,
dtype=tensor.dtype.base_dtype,
name='loss_weight')
loss = tf.mul(weight, tf.reduce_sum(tf.abs(tensor)), name='value')
tf.add_to_collection(LOSSES_COLLECTION, loss)
return loss
def l2_loss(tensor, weight=1.0, scope=None):
"""Define a L2Loss, useful for regularize, i.e. weight decay.
Args:
tensor: tensor to regularize.
weight: an optional weight to modulate the loss.
scope: Optional scope for op_scope.
Returns:
the L2 loss op.
"""
with tf.op_scope([tensor], scope, 'L2Loss'):
weight = tf.convert_to_tensor(weight,
dtype=tensor.dtype.base_dtype,
name='loss_weight')
loss = tf.mul(weight, tf.nn.l2_loss(tensor), name='value')
tf.add_to_collection(LOSSES_COLLECTION, loss)
return loss
def cross_entropy_loss(logits, one_hot_labels, label_smoothing=0,
weight=1.0, scope=None):
"""Define a Cross Entropy loss using softmax_cross_entropy_with_logits.
It can scale the loss by weight factor, and smooth the labels.
Args:
logits: [batch_size, num_classes] logits outputs of the network .
one_hot_labels: [batch_size, num_classes] target one_hot_encoded labels.
label_smoothing: if greater than 0 then smooth the labels.
weight: scale the loss by this factor.
scope: Optional scope for op_scope.
Returns:
A tensor with the softmax_cross_entropy loss.
"""
logits.get_shape().assert_is_compatible_with(one_hot_labels.get_shape())
with tf.op_scope([logits, one_hot_labels], scope, 'CrossEntropyLoss'):
num_classes = one_hot_labels.get_shape()[-1].value
one_hot_labels = tf.cast(one_hot_labels, logits.dtype)
if label_smoothing > 0:
smooth_positives = 1.0 - label_smoothing
smooth_negatives = label_smoothing / num_classes
one_hot_labels = one_hot_labels * smooth_positives + smooth_negatives
cross_entropy = tf.nn.softmax_cross_entropy_with_logits(logits,
one_hot_labels,
name='xentropy')
weight = tf.convert_to_tensor(weight,
dtype=logits.dtype.base_dtype,
name='loss_weight')
loss = tf.mul(weight, tf.reduce_mean(cross_entropy), name='value')
tf.add_to_collection(LOSSES_COLLECTION, loss)
return loss
