import math
import torch
import torch.nn as nn
from mmcv.cnn import ConvModule, DepthwiseSeparableConvModule
from mmcv.runner import BaseModule
from ..builder import NECKS
from ..utils import CSPLayer
[文档]@NECKS.register_module()
class YOLOXPAFPN(BaseModule):
"""Path Aggregation Network used in YOLOX.
Args:
in_channels (List[int]): Number of input channels per scale.
out_channels (int): Number of output channels (used at each scale)
num_csp_blocks (int): Number of bottlenecks in CSPLayer. Default: 3
use_depthwise (bool): Whether to depthwise separable convolution in
blocks. Default: False
upsample_cfg (dict): Config dict for interpolate layer.
Default: `dict(scale_factor=2, mode='nearest')`
conv_cfg (dict, optional): Config dict for convolution layer.
Default: None, which means using conv2d.
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='BN')
act_cfg (dict): Config dict for activation layer.
Default: dict(type='Swish')
init_cfg (dict or list[dict], optional): Initialization config dict.
Default: None.
"""
def __init__(self,
in_channels,
out_channels,
num_csp_blocks=3,
use_depthwise=False,
upsample_cfg=dict(scale_factor=2, mode='nearest'),
conv_cfg=None,
norm_cfg=dict(type='BN', momentum=0.03, eps=0.001),
act_cfg=dict(type='Swish'),
init_cfg=dict(
type='Kaiming',
layer='Conv2d',
a=math.sqrt(5),
distribution='uniform',
mode='fan_in',
nonlinearity='leaky_relu')):
super(YOLOXPAFPN, self).__init__(init_cfg)
self.in_channels = in_channels
self.out_channels = out_channels
conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
# build top-down blocks
self.upsample = nn.Upsample(**upsample_cfg)
self.reduce_layers = nn.ModuleList()
self.top_down_blocks = nn.ModuleList()
for idx in range(len(in_channels) - 1, 0, -1):
self.reduce_layers.append(
ConvModule(
in_channels[idx],
in_channels[idx - 1],
1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
self.top_down_blocks.append(
CSPLayer(
in_channels[idx - 1] * 2,
in_channels[idx - 1],
num_blocks=num_csp_blocks,
add_identity=False,
use_depthwise=use_depthwise,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
# build bottom-up blocks
self.downsamples = nn.ModuleList()
self.bottom_up_blocks = nn.ModuleList()
for idx in range(len(in_channels) - 1):
self.downsamples.append(
conv(
in_channels[idx],
in_channels[idx],
3,
stride=2,
padding=1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
self.bottom_up_blocks.append(
CSPLayer(
in_channels[idx] * 2,
in_channels[idx + 1],
num_blocks=num_csp_blocks,
add_identity=False,
use_depthwise=use_depthwise,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
self.out_convs = nn.ModuleList()
for i in range(len(in_channels)):
self.out_convs.append(
ConvModule(
in_channels[i],
out_channels,
1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
[文档] def forward(self, inputs):
"""
Args:
inputs (tuple[Tensor]): input features.
Returns:
tuple[Tensor]: YOLOXPAFPN features.
"""
assert len(inputs) == len(self.in_channels)
# top-down path
inner_outs = [inputs[-1]]
for idx in range(len(self.in_channels) - 1, 0, -1):
feat_heigh = inner_outs[0]
feat_low = inputs[idx - 1]
feat_heigh = self.reduce_layers[len(self.in_channels) - 1 - idx](
feat_heigh)
inner_outs[0] = feat_heigh
upsample_feat = self.upsample(feat_heigh)
inner_out = self.top_down_blocks[len(self.in_channels) - 1 - idx](
torch.cat([upsample_feat, feat_low], 1))
inner_outs.insert(0, inner_out)
# bottom-up path
outs = [inner_outs[0]]
for idx in range(len(self.in_channels) - 1):
feat_low = outs[-1]
feat_height = inner_outs[idx + 1]
downsample_feat = self.downsamples[idx](feat_low)
out = self.bottom_up_blocks[idx](
torch.cat([downsample_feat, feat_height], 1))
outs.append(out)
# out convs
for idx, conv in enumerate(self.out_convs):
outs[idx] = conv(outs[idx])
return tuple(outs)