res_second.py

# modified from https://github.com/Haiyang-W/DSVT

import warnings
from typing import Optional, Sequence, Tuple

from mmengine.model import BaseModule
from torch import Tensor
from torch import nn as nn

from mmdet3d.registry import MODELS
from mmdet3d.utils import OptMultiConfig


class BasicResBlock(nn.Module):
    expansion: int = 1

    def __init__(
        self,
        inplanes: int,
        planes: int,
        stride: int = 1,
        padding: int = 1,
        downsample: bool = False,
    ) -> None:
        super().__init__()
        self.conv1 = nn.Conv2d(
            inplanes,
            planes,
            kernel_size=3,
            stride=stride,
            padding=padding,
            bias=False)
        self.bn1 = nn.BatchNorm2d(planes, eps=1e-3, momentum=0.01)
        self.relu1 = nn.ReLU()
        self.conv2 = nn.Conv2d(
            planes, planes, kernel_size=3, padding=1, bias=False)
        self.bn2 = nn.BatchNorm2d(planes, eps=1e-3, momentum=0.01)
        self.relu2 = nn.ReLU()
        self.downsample = downsample
        if self.downsample:
            self.downsample_layer = nn.Sequential(
                nn.Conv2d(
                    inplanes,
                    planes,
                    kernel_size=1,
                    stride=stride,
                    padding=0,
                    bias=False),
                nn.BatchNorm2d(planes, eps=1e-3, momentum=0.01))
        self.stride = stride

    def forward(self, x: Tensor) -> Tensor:
        identity = x

        out = self.conv1(x)
        out = self.bn1(out)
        out = self.relu1(out)

        out = self.conv2(out)
        out = self.bn2(out)

        if self.downsample:
            identity = self.downsample_layer(x)

        out += identity
        out = self.relu2(out)

        return out


@MODELS.register_module()
class ResSECOND(BaseModule):
    """Backbone network for DSVT. The difference between `ResSECOND` and
    `SECOND` is that the basic block in this module contains residual layers.

    Args:
        in_channels (int): Input channels.
        out_channels (list[int]): Output channels for multi-scale feature maps.
        blocks_nums (list[int]): Number of blocks in each stage.
        layer_strides (list[int]): Strides of each stage.
        norm_cfg (dict): Config dict of normalization layers.
        conv_cfg (dict): Config dict of convolutional layers.
    """

    def __init__(self,
                 in_channels: int = 128,
                 out_channels: Sequence[int] = [128, 128, 256],
                 blocks_nums: Sequence[int] = [1, 2, 2],
                 layer_strides: Sequence[int] = [2, 2, 2],
                 init_cfg: OptMultiConfig = None,
                 pretrained: Optional[str] = None) -> None:
        super(ResSECOND, self).__init__(init_cfg=init_cfg)
        assert len(layer_strides) == len(blocks_nums)
        assert len(out_channels) == len(blocks_nums)

        in_filters = [in_channels, *out_channels[:-1]]
        blocks = []
        for i, block_num in enumerate(blocks_nums):
            cur_layers = [
                BasicResBlock(
                    in_filters[i],
                    out_channels[i],
                    stride=layer_strides[i],
                    downsample=True)
            ]
            for _ in range(block_num):
                cur_layers.append(
                    BasicResBlock(out_channels[i], out_channels[i]))
            blocks.append(nn.Sequential(*cur_layers))
        self.blocks = nn.Sequential(*blocks)
        assert not (init_cfg and pretrained), \
            'init_cfg and pretrained cannot be setting at the same time'
        if isinstance(pretrained, str):
            warnings.warn('DeprecationWarning: pretrained is a deprecated, '
                          'please use "init_cfg" instead')
            self.init_cfg = dict(type='Pretrained', checkpoint=pretrained)
        else:
            self.init_cfg = dict(type='Kaiming', layer='Conv2d')

    def forward(self, x: Tensor) -> Tuple[Tensor, ...]:
        """Forward function.

        Args:
            x (torch.Tensor): Input with shape (N, C, H, W).

        Returns:
            tuple[torch.Tensor]: Multi-scale features.
        """
        outs = []
        for i in range(len(self.blocks)):
            x = self.blocks[i](x)
            outs.append(x)
        return tuple(outs)