Source code for mmaction.models.heads.tpn_head

# Copyright (c) OpenMMLab. All rights reserved.
from typing import Optional

import torch.nn as nn
from mmengine.device import get_device
from torch import Tensor

from mmaction.registry import MODELS
from .tsn_head import TSNHead


@MODELS.register_module()
class TPNHead(TSNHead):
    """Class head for TPN."""

    def __init__(self, *args, **kwargs) -> None:
        super().__init__(*args, **kwargs)

        if self.spatial_type == 'avg':
            # use `nn.AdaptiveAvgPool3d` to adaptively match the in_channels.
            self.avg_pool3d = nn.AdaptiveAvgPool3d((1, 1, 1))
        else:
            self.avg_pool3d = None

        self.avg_pool2d = None
        self.new_cls = None

    def _init_new_cls(self) -> None:
        self.new_cls = nn.Conv3d(self.in_channels, self.num_classes, 1, 1, 0)
        self.new_cls = self.new_cls.to(get_device())
        self.new_cls.weight.copy_(self.fc_cls.weight[..., None, None, None])
        self.new_cls.bias.copy_(self.fc_cls.bias)

    def forward(self,
                x,
                num_segs: Optional[int] = None,
                fcn_test: bool = False,
                **kwargs) -> Tensor:
        """Defines the computation performed at every call.

        Args:
            x (Tensor): The input data.
            num_segs (int, optional): Number of segments into which a video
                is divided. Defaults to None.
            fcn_test (bool): Whether to apply full convolution (fcn) testing.
                Defaults to False.

        Returns:
            Tensor: The classification scores for input samples.
        """
        if fcn_test:
            if self.avg_pool3d:
                x = self.avg_pool3d(x)
            if self.new_cls is None:
                self._init_new_cls()
            x = self.new_cls(x)
            cls_score_feat_map = x.view(x.size(0), -1)
            return cls_score_feat_map

        if self.avg_pool2d is None:
            kernel_size = (1, x.shape[-2], x.shape[-1])
            self.avg_pool2d = nn.AvgPool3d(kernel_size, stride=1, padding=0)

        if num_segs is None:
            # [N, in_channels, 3, 7, 7]
            x = self.avg_pool3d(x)
        else:
            # [N * num_segs, in_channels, 7, 7]
            x = self.avg_pool2d(x)
            # [N * num_segs, in_channels, 1, 1]
            x = x.reshape((-1, num_segs) + x.shape[1:])
            # [N, num_segs, in_channels, 1, 1]
            x = self.consensus(x)
            # [N, 1, in_channels, 1, 1]
            x = x.squeeze(1)
            # [N, in_channels, 1, 1]
        if self.dropout is not None:
            x = self.dropout(x)
            # [N, in_channels, 1, 1]
        x = x.view(x.size(0), -1)
        # [N, in_channels]
        cls_score = self.fc_cls(x)
        # [N, num_classes]
        return cls_score