mmdetection/mmdet/models/layers/csp_layer.py

# Copyright (c) OpenMMLab. All rights reserved.
import torch
import torch.nn as nn
from mmcv.cnn import ConvModule, DepthwiseSeparableConvModule
from mmengine.model import BaseModule
from torch import Tensor

from mmdet.utils import ConfigType, OptConfigType, OptMultiConfig
from .se_layer import ChannelAttention


class DarknetBottleneck(BaseModule):
    """The basic bottleneck block used in Darknet.

    Each ResBlock consists of two ConvModules and the input is added to the
    final output. Each ConvModule is composed of Conv, BN, and LeakyReLU.
    The first convLayer has filter size of 1x1 and the second one has the
    filter size of 3x3.

    Args:
        in_channels (int): The input channels of this Module.
        out_channels (int): The output channels of this Module.
        expansion (float): The kernel size of the convolution.
            Defaults to 0.5.
        add_identity (bool): Whether to add identity to the out.
            Defaults to True.
        use_depthwise (bool): Whether to use depthwise separable convolution.
            Defaults to False.
        conv_cfg (dict): Config dict for convolution layer. Defaults to None,
            which means using conv2d.
        norm_cfg (dict): Config dict for normalization layer.
            Defaults to dict(type='BN').
        act_cfg (dict): Config dict for activation layer.
            Defaults to dict(type='Swish').
    """

    def __init__(self,
                 in_channels: int,
                 out_channels: int,
                 expansion: float = 0.5,
                 add_identity: bool = True,
                 use_depthwise: bool = False,
                 conv_cfg: OptConfigType = None,
                 norm_cfg: ConfigType = dict(
                     type='BN', momentum=0.03, eps=0.001),
                 act_cfg: ConfigType = dict(type='Swish'),
                 init_cfg: OptMultiConfig = None) -> None:
        super().__init__(init_cfg=init_cfg)
        hidden_channels = int(out_channels * expansion)
        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
        self.conv1 = ConvModule(
            in_channels,
            hidden_channels,
            1,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.conv2 = conv(
            hidden_channels,
            out_channels,
            3,
            stride=1,
            padding=1,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.add_identity = \
            add_identity and in_channels == out_channels

    def forward(self, x: Tensor) -> Tensor:
        """Forward function."""
        identity = x
        out = self.conv1(x)
        out = self.conv2(out)

        if self.add_identity:
            return out + identity
        else:
            return out


class CSPNeXtBlock(BaseModule):
    """The basic bottleneck block used in CSPNeXt.

    Args:
        in_channels (int): The input channels of this Module.
        out_channels (int): The output channels of this Module.
        expansion (float): Expand ratio of the hidden channel. Defaults to 0.5.
        add_identity (bool): Whether to add identity to the out. Only works
            when in_channels == out_channels. Defaults to True.
        use_depthwise (bool): Whether to use depthwise separable convolution.
            Defaults to False.
        kernel_size (int): The kernel size of the second convolution layer.
            Defaults to 5.
        conv_cfg (dict): Config dict for convolution layer. Defaults to None,
            which means using conv2d.
        norm_cfg (dict): Config dict for normalization layer.
            Defaults to dict(type='BN', momentum=0.03, eps=0.001).
        act_cfg (dict): Config dict for activation layer.
            Defaults to dict(type='SiLU').
        init_cfg (:obj:`ConfigDict` or dict or list[dict] or
            list[:obj:`ConfigDict`], optional): Initialization config dict.
            Defaults to None.
    """

    def __init__(self,
                 in_channels: int,
                 out_channels: int,
                 expansion: float = 0.5,
                 add_identity: bool = True,
                 use_depthwise: bool = False,
                 kernel_size: int = 5,
                 conv_cfg: OptConfigType = None,
                 norm_cfg: ConfigType = dict(
                     type='BN', momentum=0.03, eps=0.001),
                 act_cfg: ConfigType = dict(type='SiLU'),
                 init_cfg: OptMultiConfig = None) -> None:
        super().__init__(init_cfg=init_cfg)
        hidden_channels = int(out_channels * expansion)
        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
        self.conv1 = conv(
            in_channels,
            hidden_channels,
            3,
            stride=1,
            padding=1,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.conv2 = DepthwiseSeparableConvModule(
            hidden_channels,
            out_channels,
            kernel_size,
            stride=1,
            padding=kernel_size // 2,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.add_identity = \
            add_identity and in_channels == out_channels

    def forward(self, x: Tensor) -> Tensor:
        """Forward function."""
        identity = x
        out = self.conv1(x)
        out = self.conv2(out)

        if self.add_identity:
            return out + identity
        else:
            return out


class CSPLayer(BaseModule):
    """Cross Stage Partial Layer.

    Args:
        in_channels (int): The input channels of the CSP layer.
        out_channels (int): The output channels of the CSP layer.
        expand_ratio (float): Ratio to adjust the number of channels of the
            hidden layer. Defaults to 0.5.
        num_blocks (int): Number of blocks. Defaults to 1.
        add_identity (bool): Whether to add identity in blocks.
            Defaults to True.
        use_cspnext_block (bool): Whether to use CSPNeXt block.
            Defaults to False.
        use_depthwise (bool): Whether to use depthwise separable convolution in
            blocks. Defaults to False.
        channel_attention (bool): Whether to add channel attention in each
            stage. Defaults to True.
        conv_cfg (dict, optional): Config dict for convolution layer.
            Defaults to None, which means using conv2d.
        norm_cfg (dict): Config dict for normalization layer.
            Defaults to dict(type='BN')
        act_cfg (dict): Config dict for activation layer.
            Defaults to dict(type='Swish')
        init_cfg (:obj:`ConfigDict` or dict or list[dict] or
            list[:obj:`ConfigDict`], optional): Initialization config dict.
            Defaults to None.
    """

    def __init__(self,
                 in_channels: int,
                 out_channels: int,
                 expand_ratio: float = 0.5,
                 num_blocks: int = 1,
                 add_identity: bool = True,
                 use_depthwise: bool = False,
                 use_cspnext_block: bool = False,
                 channel_attention: bool = False,
                 conv_cfg: OptConfigType = None,
                 norm_cfg: ConfigType = dict(
                     type='BN', momentum=0.03, eps=0.001),
                 act_cfg: ConfigType = dict(type='Swish'),
                 init_cfg: OptMultiConfig = None) -> None:
        super().__init__(init_cfg=init_cfg)
        block = CSPNeXtBlock if use_cspnext_block else DarknetBottleneck
        mid_channels = int(out_channels * expand_ratio)
        self.channel_attention = channel_attention
        self.main_conv = ConvModule(
            in_channels,
            mid_channels,
            1,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.short_conv = ConvModule(
            in_channels,
            mid_channels,
            1,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)
        self.final_conv = ConvModule(
            2 * mid_channels,
            out_channels,
            1,
            conv_cfg=conv_cfg,
            norm_cfg=norm_cfg,
            act_cfg=act_cfg)

        self.blocks = nn.Sequential(*[
            block(
                mid_channels,
                mid_channels,
                1.0,
                add_identity,
                use_depthwise,
                conv_cfg=conv_cfg,
                norm_cfg=norm_cfg,
                act_cfg=act_cfg) for _ in range(num_blocks)
        ])
        if channel_attention:
            self.attention = ChannelAttention(2 * mid_channels)

    def forward(self, x: Tensor) -> Tensor:
        """Forward function."""
        x_short = self.short_conv(x)

        x_main = self.main_conv(x)
        x_main = self.blocks(x_main)

        x_final = torch.cat((x_main, x_short), dim=1)

        if self.channel_attention:
            x_final = self.attention(x_final)
        return self.final_conv(x_final)