resnet.py

# copyright (c) 2021 PaddlePaddle Authors. All Rights Reserve.
#
# 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.

import paddle
import paddle.nn as nn
import paddle.nn.functional as F

from paddleseg.models import layers
from paddleseg.utils import utils

__all__ = ["ResNet50_vd"]


class ConvBNLayer(nn.Layer):
    """Basic conv bn relu layer."""
    
    def __init__(
            self,
            in_channels: int,
            out_channels: int,
            kernel_size: int,
            stride: int = 1,
            dilation: int = 1,
            groups: int = 1,
            is_vd_mode: bool = False,
            act: str = None,
    ):
        super(ConvBNLayer, self).__init__()

        self.is_vd_mode = is_vd_mode
        self._pool2d_avg = nn.AvgPool2D(
            kernel_size=2, stride=2, padding=0, ceil_mode=True)
        self._conv = nn.Conv2D(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=(kernel_size - 1) // 2 if dilation == 1 else 0,
            dilation=dilation,
            groups=groups,
            bias_attr=False)

        self._batch_norm = layers.SyncBatchNorm(out_channels)
        self._act_op = layers.Activation(act=act)

    def forward(self, inputs: paddle.Tensor) -> paddle.Tensor:
        if self.is_vd_mode:
            inputs = self._pool2d_avg(inputs)
        y = self._conv(inputs)
        y = self._batch_norm(y)
        y = self._act_op(y)

        return y


class BottleneckBlock(nn.Layer):
    """Residual bottleneck block"""
    
    def __init__(self,
                 in_channels: int,
                 out_channels: int,
                 stride: int,
                 shortcut: bool = True,
                 if_first: bool = False,
                 dilation: int = 1):
        super(BottleneckBlock, self).__init__()

        self.conv0 = ConvBNLayer(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=1,
            act='relu')

        self.dilation = dilation

        self.conv1 = ConvBNLayer(
            in_channels=out_channels,
            out_channels=out_channels,
            kernel_size=3,
            stride=stride,
            act='relu',
            dilation=dilation)
        self.conv2 = ConvBNLayer(
            in_channels=out_channels,
            out_channels=out_channels * 4,
            kernel_size=1,
            act=None)

        if not shortcut:
            self.short = ConvBNLayer(
                in_channels=in_channels,
                out_channels=out_channels * 4,
                kernel_size=1,
                stride=1,
                is_vd_mode=False if if_first or stride == 1 else True)

        self.shortcut = shortcut

    def forward(self, inputs: paddle.Tensor) -> paddle.Tensor:
        y = self.conv0(inputs)

        ####################################################################
        # If given dilation rate > 1, using corresponding padding.
        # The performance drops down without the follow padding.
        if self.dilation > 1:
            padding = self.dilation
            y = F.pad(y, [padding, padding, padding, padding])
        #####################################################################

        conv1 = self.conv1(y)
        conv2 = self.conv2(conv1)

        if self.shortcut:
            short = inputs
        else:
            short = self.short(inputs)

        y = paddle.add(x=short, y=conv2)
        y = F.relu(y)
        return y


class BasicBlock(nn.Layer):
    """Basic residual block"""
    def __init__(self,
                 in_channels: int,
                 out_channels: int,
                 stride: int,
                 shortcut: bool = True,
                 if_first: bool = False):
        super(BasicBlock, self).__init__()
        self.stride = stride
        self.conv0 = ConvBNLayer(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=3,
            stride=stride,
            act='relu')
        self.conv1 = ConvBNLayer(
            in_channels=out_channels,
            out_channels=out_channels,
            kernel_size=3,
            act=None)

        if not shortcut:
            self.short = ConvBNLayer(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=1,
                stride=1,
                is_vd_mode=False if if_first else True)

        self.shortcut = shortcut

    def forward(self, inputs: paddle.Tensor) -> paddle.Tensor:
        y = self.conv0(inputs)
        conv1 = self.conv1(y)

        if self.shortcut:
            short = inputs
        else:
            short = self.short(inputs)
        y = paddle.add(x=short, y=conv1)
        y = F.relu(y)

        return y


class ResNet_vd(nn.Layer):
    """
    The ResNet_vd implementation based on PaddlePaddle.

    The original article refers to Jingdong
    Tong He, et, al. "Bag of Tricks for Image Classification with Convolutional Neural Networks"
    (https://arxiv.org/pdf/1812.01187.pdf).

    """

    def __init__(self,
                 input_channels: int = 3,
                 layers: int = 50,
                 output_stride: int = 32,
                 multi_grid: tuple = (1, 1, 1),
                 pretrained: str = None):
        super(ResNet_vd, self).__init__()

        self.conv1_logit = None  # for gscnn shape stream
        self.layers = layers
        supported_layers = [18, 34, 50, 101, 152, 200]
        assert layers in supported_layers, \
            "supported layers are {} but input layer is {}".format(
                supported_layers, layers)

        if layers == 18:
            depth = [2, 2, 2, 2]
        elif layers == 34 or layers == 50:
            depth = [3, 4, 6, 3]
        elif layers == 101:
            depth = [3, 4, 23, 3]
        elif layers == 152:
            depth = [3, 8, 36, 3]
        elif layers == 200:
            depth = [3, 12, 48, 3]
        num_channels = [64, 256, 512, 1024
                        ] if layers >= 50 else [64, 64, 128, 256]
        num_filters = [64, 128, 256, 512]

        # for channels of four returned stages
        self.feat_channels = [c * 4 for c in num_filters
                              ] if layers >= 50 else num_filters
        self.feat_channels = [64] + self.feat_channels

        dilation_dict = None
        if output_stride == 8:
            dilation_dict = {2: 2, 3: 4}
        elif output_stride == 16:
            dilation_dict = {3: 2}

        self.conv1_1 = ConvBNLayer(
            in_channels=input_channels,
            out_channels=32,
            kernel_size=3,
            stride=2,
            act='relu')
        self.conv1_2 = ConvBNLayer(
            in_channels=32,
            out_channels=32,
            kernel_size=3,
            stride=1,
            act='relu')
        self.conv1_3 = ConvBNLayer(
            in_channels=32,
            out_channels=64,
            kernel_size=3,
            stride=1,
            act='relu')
        self.pool2d_max = nn.MaxPool2D(kernel_size=3, stride=2, padding=1)

        # self.block_list = []
        self.stage_list = []
        if layers >= 50:
            for block in range(len(depth)):
                shortcut = False
                block_list = []
                for i in range(depth[block]):
                    if layers in [101, 152] and block == 2:
                        if i == 0:
                            conv_name = "res" + str(block + 2) + "a"
                        else:
                            conv_name = "res" + str(block + 2) + "b" + str(i)
                    else:
                        conv_name = "res" + str(block + 2) + chr(97 + i)

                    ###############################################################################
                    # Add dilation rate for some segmentation tasks, if dilation_dict is not None.
                    dilation_rate = dilation_dict[
                        block] if dilation_dict and block in dilation_dict else 1

                    # Actually block here is 'stage', and i is 'block' in 'stage'
                    # At the stage 4, expand the the dilation_rate if given multi_grid
                    if block == 3:
                        dilation_rate = dilation_rate * multi_grid[i]
                    ###############################################################################

                    bottleneck_block = self.add_sublayer(
                        'bb_%d_%d' % (block, i),
                        BottleneckBlock(
                            in_channels=num_channels[block]
                            if i == 0 else num_filters[block] * 4,
                            out_channels=num_filters[block],
                            stride=2 if i == 0 and block != 0
                            and dilation_rate == 1 else 1,
                            shortcut=shortcut,
                            if_first=block == i == 0,
                            dilation=dilation_rate))

                    block_list.append(bottleneck_block)
                    shortcut = True
                self.stage_list.append(block_list)
        else:
            for block in range(len(depth)):
                shortcut = False
                block_list = []
                for i in range(depth[block]):
                    conv_name = "res" + str(block + 2) + chr(97 + i)
                    basic_block = self.add_sublayer(
                        'bb_%d_%d' % (block, i),
                        BasicBlock(
                            in_channels=num_channels[block]
                            if i == 0 else num_filters[block],
                            out_channels=num_filters[block],
                            stride=2 if i == 0 and block != 0 else 1,
                            shortcut=shortcut,
                            if_first=block == i == 0))
                    block_list.append(basic_block)
                    shortcut = True
                self.stage_list.append(block_list)

        self.pretrained = pretrained

    def forward(self, inputs: paddle.Tensor) -> paddle.Tensor:
        feat_list = []
        y = self.conv1_1(inputs)
        y = self.conv1_2(y)
        y = self.conv1_3(y)
        feat_list.append(y)

        y = self.pool2d_max(y)

        # A feature list saves the output feature map of each stage.
        for stage in self.stage_list:
            for block in stage:
                y = block(y)
            feat_list.append(y)

        return feat_list


def ResNet50_vd(**args):
    model = ResNet_vd(layers=50, **args)
    return model