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# coding=utf-8
# Copyright 2021 The Deeplab2 Authors.
#
# 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.
"""This file contains code to build an ASPP layer.
Reference:
- [Rethinking Atrous Convolution for Semantic Image Segmentation](
https://arxiv.org/pdf/1706.05587.pdf)
- [ParseNet: Looking Wider to See Better](
https://arxiv.org/pdf/1506.04579.pdf).
"""
from absl import logging
import tensorflow as tf
from deeplab2.model import utils
from deeplab2.model.layers import convolutions
layers = tf.keras.layers
backend = tf.keras.backend
class ASPPConv(tf.keras.layers.Layer):
"""An atrous convolution for ASPP."""
def __init__(self,
output_channels,
atrous_rate,
name,
bn_layer=tf.keras.layers.BatchNormalization):
"""Creates a atrous convolution layer for the ASPP.
This layer consists of an atrous convolution followed by a BatchNorm layer
and a ReLU activation.
Args:
output_channels: An integer specifying the number of output channels of
the convolution.
atrous_rate: An integer specifying the atrous/dilation rate of the
convolution.
name: A string specifying the name of this layer.
bn_layer: An optional tf.keras.layers.Layer that computes the
normalization (default: tf.keras.layers.BatchNormalization).
"""
super(ASPPConv, self).__init__(name=name)
self._conv_bn_act = convolutions.Conv2DSame(
output_channels,
kernel_size=3,
name='conv_bn_act',
atrous_rate=atrous_rate,
use_bias=False,
use_bn=True,
bn_layer=bn_layer,
activation='relu')
def call(self, input_tensor, training=False):
"""Performs a forward pass.
Args:
input_tensor: An input tensor of type tf.Tensor with shape [batch, height,
width, channels].
training: A boolean flag indicating whether training behavior should be
used (default: False).
Returns:
The output tensor.
"""
return self._conv_bn_act(input_tensor, training=training)
class ASPPPool(tf.keras.layers.Layer):
"""A pooling layer for ASPP."""
def __init__(self,
output_channels,
name,
bn_layer=tf.keras.layers.BatchNormalization):
"""Creates a pooling layer for the ASPP.
This layer consists of a global average pooling, followed by a convolution,
and by a BatchNorm layer and a ReLU activation.
Args:
output_channels: An integer specifying the number of output channels of
the convolution.
name: A string specifying the name of this layer.
bn_layer: An optional tf.keras.layers.Layer that computes the
normalization (default: tf.keras.layers.BatchNormalization).
"""
super(ASPPPool, self).__init__(name=name)
self._pool_size = (None, None)
self._conv_bn_act = convolutions.Conv2DSame(
output_channels,
kernel_size=1,
name='conv_bn_act',
use_bias=False,
use_bn=True,
bn_layer=bn_layer,
activation='relu')
def set_pool_size(self, pool_size):
"""Sets the pooling size of the pooling layer.
The default behavior of the pooling layer is global average pooling. A
custom pooling size can be set here.
Args:
pool_size: A tuple specifying the pooling size of the pooling layer.
Raises:
An error occurs if exactly one pooling dimension is set to 'None'.
"""
# If exactly one pooling dimension is 'None' raise an error.
if None in pool_size and pool_size != (None, None):
raise ValueError('The ASPP pooling layer requires that the pooling size '
'is set explicitly for both dimensions. In case, global '
'average pooling should be used, call '
'reset_pooling_layer() or set both to None.')
self._pool_size = pool_size
logging.info('Global average pooling in the ASPP pooling layer was replaced'
' with tiled average pooling using the provided pool_size. '
'Please make sure this behavior is intended.')
def get_pool_size(self):
return self._pool_size
def reset_pooling_layer(self):
"""Resets the pooling layer to global average pooling."""
self._pool_size = (None, None)
def call(self, input_tensor, training=False):
"""Performs a forward pass.
Args:
input_tensor: An input tensor of type tf.Tensor with shape [batch, height,
width, channels].
training: A boolean flag indicating whether training behavior should be
used (default: False).
Returns:
The output tensor.
"""
if tuple(self._pool_size) == (None, None):
# Global image pooling
pool_size = input_tensor.shape[1:3]
else:
# Tiled image pooling
pool_size = self._pool_size
x = backend.pool2d(input_tensor, pool_size, padding='valid',
pool_mode='avg')
x = self._conv_bn_act(x, training=training)
target_h = tf.shape(input_tensor)[1]
target_w = tf.shape(input_tensor)[2]
x = utils.resize_align_corners(x, [target_h, target_w])
return x
class ASPP(tf.keras.layers.Layer):
"""An atrous spatial pyramid pooling layer."""
def __init__(self,
output_channels,
atrous_rates,
aspp_use_only_1x1_proj_conv=False,
name='ASPP',
bn_layer=tf.keras.layers.BatchNormalization):
"""Creates an ASPP layer.
Args:
output_channels: An integer specifying the number of output channels of
each ASPP convolution layer.
atrous_rates: A list of three integers specifying the atrous/dilation rate
of each ASPP convolution layer.
aspp_use_only_1x1_proj_conv: Boolean, specifying if the ASPP five branches
are turned off or not. If True, the ASPP module is degenerated to one
1x1 convolution, projecting the input channels to `output_channels`.
name: A string specifying the name of this layer (default: 'ASPP').
bn_layer: An optional tf.keras.layers.Layer that computes the
normalization (default: tf.keras.layers.BatchNormalization).
Raises:
ValueError: An error occurs when both atrous_rates does not contain 3
elements and `aspp_use_only_1x1_proj_conv` is False.
"""
super(ASPP, self).__init__(name=name)
if not aspp_use_only_1x1_proj_conv and len(atrous_rates) != 3:
raise ValueError(
'The ASPP layers need exactly 3 atrous rates, but %d were given' %
len(atrous_rates))
self._aspp_use_only_1x1_proj_conv = aspp_use_only_1x1_proj_conv
# Projection convolution is always used.
self._proj_conv_bn_act = convolutions.Conv2DSame(
output_channels,
kernel_size=1,
name='proj_conv_bn_act',
use_bias=False,
use_bn=True,
bn_layer=bn_layer,
activation='relu')
if not aspp_use_only_1x1_proj_conv:
self._conv_bn_act = convolutions.Conv2DSame(
output_channels,
kernel_size=1,
name='conv_bn_act',
use_bias=False,
use_bn=True,
bn_layer=bn_layer,
activation='relu')
rate1, rate2, rate3 = atrous_rates
self._aspp_conv1 = ASPPConv(output_channels, rate1, name='aspp_conv1',
bn_layer=bn_layer)
self._aspp_conv2 = ASPPConv(output_channels, rate2, name='aspp_conv2',
bn_layer=bn_layer)
self._aspp_conv3 = ASPPConv(output_channels, rate3, name='aspp_conv3',
bn_layer=bn_layer)
self._aspp_pool = ASPPPool(output_channels, name='aspp_pool',
bn_layer=bn_layer)
# Dropout is needed only when ASPP five branches are used.
self._proj_drop = layers.Dropout(rate=0.1)
def set_pool_size(self, pool_size):
"""Sets the pooling size of the ASPP pooling layer.
The default behavior of the pooling layer is global average pooling. A
custom pooling size can be set here.
Args:
pool_size: A tuple specifying the pooling size of the ASPP pooling layer.
"""
if not self._aspp_use_only_1x1_proj_conv:
self._aspp_pool.set_pool_size(pool_size)
def get_pool_size(self):
if not self._aspp_use_only_1x1_proj_conv:
return self._aspp_pool.get_pool_size()
else:
return (None, None)
def reset_pooling_layer(self):
"""Resets the pooling layer to global average pooling."""
self._aspp_pool.reset_pooling_layer()
def call(self, input_tensor, training=False):
"""Performs a forward pass.
Args:
input_tensor: An input tensor of type tf.Tensor with shape [batch, height,
width, channels].
training: A boolean flag indicating whether training behavior should be
used (default: False).
Returns:
The output tensor.
"""
if self._aspp_use_only_1x1_proj_conv:
x = self._proj_conv_bn_act(input_tensor, training=training)
else:
# Apply the ASPP module.
results = []
results.append(self._conv_bn_act(input_tensor, training=training))
results.append(self._aspp_conv1(input_tensor, training=training))
results.append(self._aspp_conv2(input_tensor, training=training))
results.append(self._aspp_conv3(input_tensor, training=training))
results.append(self._aspp_pool(input_tensor, training=training))
x = tf.concat(results, 3)
x = self._proj_conv_bn_act(x, training=training)
x = self._proj_drop(x, training=training)
return x
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