# Source code for monai.networks.blocks.aspp

```
# Copyright 2020 - 2021 MONAI Consortium
# 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.
from typing import Optional, Sequence, Tuple, Union
import torch
import torch.nn as nn
from monai.networks.blocks.convolutions import Convolution
from monai.networks.layers import same_padding
from monai.networks.layers.factories import Conv
[docs]class SimpleASPP(nn.Module):
"""
A simplified version of the atrous spatial pyramid pooling (ASPP) module.
Chen et al., Encoder-Decoder with Atrous Separable Convolution for Semantic Image Segmentation.
https://arxiv.org/abs/1802.02611
Wang et al., A Noise-robust Framework for Automatic Segmentation of COVID-19 Pneumonia Lesions
from CT Images. https://ieeexplore.ieee.org/document/9109297
"""
[docs] def __init__(
self,
spatial_dims: int,
in_channels: int,
conv_out_channels: int,
kernel_sizes: Sequence[int] = (1, 3, 3, 3),
dilations: Sequence[int] = (1, 2, 4, 6),
norm_type: Optional[Union[Tuple, str]] = "BATCH",
acti_type: Optional[Union[Tuple, str]] = "LEAKYRELU",
bias: bool = False,
) -> None:
"""
Args:
spatial_dims: number of spatial dimensions, could be 1, 2, or 3.
in_channels: number of input channels.
conv_out_channels: number of output channels of each atrous conv.
The final number of output channels is conv_out_channels * len(kernel_sizes).
kernel_sizes: a sequence of four convolutional kernel sizes.
Defaults to (1, 3, 3, 3) for four (dilated) convolutions.
dilations: a sequence of four convolutional dilation parameters.
Defaults to (1, 2, 4, 6) for four (dilated) convolutions.
norm_type: final kernel-size-one convolution normalization type.
Defaults to batch norm.
acti_type: final kernel-size-one convolution activation type.
Defaults to leaky ReLU.
bias: whether to have a bias term in convolution blocks. Defaults to False.
According to `Performance Tuning Guide <https://pytorch.org/tutorials/recipes/recipes/tuning_guide.html>`_,
if a conv layer is directly followed by a batch norm layer, bias should be False.
Raises:
ValueError: When ``kernel_sizes`` length differs from ``dilations``.
See also:
:py:class:`monai.networks.layers.Act`
:py:class:`monai.networks.layers.Conv`
:py:class:`monai.networks.layers.Norm`
"""
super().__init__()
if len(kernel_sizes) != len(dilations):
raise ValueError(
"kernel_sizes and dilations length must match, "
f"got kernel_sizes={len(kernel_sizes)} dilations={len(dilations)}."
)
pads = tuple(same_padding(k, d) for k, d in zip(kernel_sizes, dilations))
self.convs = nn.ModuleList()
for k, d, p in zip(kernel_sizes, dilations, pads):
_conv = Conv[Conv.CONV, spatial_dims](
in_channels=in_channels, out_channels=conv_out_channels, kernel_size=k, dilation=d, padding=p
)
self.convs.append(_conv)
out_channels = conv_out_channels * len(pads) # final conv. output channels
self.conv_k1 = Convolution(
spatial_dims=spatial_dims,
in_channels=out_channels,
out_channels=out_channels,
kernel_size=1,
act=acti_type,
norm=norm_type,
bias=bias,
)
[docs] def forward(self, x: torch.Tensor) -> torch.Tensor:
"""
Args:
x: in shape (batch, channel, spatial_1[, spatial_2, ...]).
"""
x_out = torch.cat([conv(x) for conv in self.convs], dim=1)
x_out = self.conv_k1(x_out)
return x_out
```