yolo_neck.py
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# Copyright (c) OpenMMLab. All rights reserved.
# Copyright (c) 2019 Western Digital Corporation or its affiliates.
import torch
import torch.nn.functional as F
from mmcv.cnn import ConvModule
from mmcv.runner import BaseModule
from ..builder import NECKS
class DetectionBlock(BaseModule):
"""Detection block in YOLO neck.
Let out_channels = n, the DetectionBlock contains:
Six ConvLayers, 1 Conv2D Layer and 1 YoloLayer.
The first 6 ConvLayers are formed the following way:
1x1xn, 3x3x2n, 1x1xn, 3x3x2n, 1x1xn, 3x3x2n.
The Conv2D layer is 1x1x255.
Some block will have branch after the fifth ConvLayer.
The input channel is arbitrary (in_channels)
Args:
in_channels (int): The number of input channels.
out_channels (int): The number of output channels.
conv_cfg (dict): Config dict for convolution layer. Default: None.
norm_cfg (dict): Dictionary to construct and config norm layer.
Default: dict(type='BN', requires_grad=True)
act_cfg (dict): Config dict for activation layer.
Default: dict(type='LeakyReLU', negative_slope=0.1).
init_cfg (dict or list[dict], optional): Initialization config dict.
Default: None
"""
def __init__(self,
in_channels,
out_channels,
conv_cfg=None,
norm_cfg=dict(type='BN', requires_grad=True),
act_cfg=dict(type='LeakyReLU', negative_slope=0.1),
init_cfg=None):
super(DetectionBlock, self).__init__(init_cfg)
double_out_channels = out_channels * 2
# shortcut
cfg = dict(conv_cfg=conv_cfg, norm_cfg=norm_cfg, act_cfg=act_cfg)
self.conv1 = ConvModule(in_channels, out_channels, 1, **cfg)
self.conv2 = ConvModule(
out_channels, double_out_channels, 3, padding=1, **cfg)
self.conv3 = ConvModule(double_out_channels, out_channels, 1, **cfg)
self.conv4 = ConvModule(
out_channels, double_out_channels, 3, padding=1, **cfg)
self.conv5 = ConvModule(double_out_channels, out_channels, 1, **cfg)
def forward(self, x):
tmp = self.conv1(x)
tmp = self.conv2(tmp)
tmp = self.conv3(tmp)
tmp = self.conv4(tmp)
out = self.conv5(tmp)
return out
@NECKS.register_module()
class YOLOV3Neck(BaseModule):
"""The neck of YOLOV3.
It can be treated as a simplified version of FPN. It
will take the result from Darknet backbone and do some upsampling and
concatenation. It will finally output the detection result.
Note:
The input feats should be from top to bottom.
i.e., from high-lvl to low-lvl
But YOLOV3Neck will process them in reversed order.
i.e., from bottom (high-lvl) to top (low-lvl)
Args:
num_scales (int): The number of scales / stages.
in_channels (List[int]): The number of input channels per scale.
out_channels (List[int]): The number of output channels per scale.
conv_cfg (dict, optional): Config dict for convolution layer.
Default: None.
norm_cfg (dict, optional): Dictionary to construct and config norm
layer. Default: dict(type='BN', requires_grad=True)
act_cfg (dict, optional): Config dict for activation layer.
Default: dict(type='LeakyReLU', negative_slope=0.1).
init_cfg (dict or list[dict], optional): Initialization config dict.
Default: None
"""
def __init__(self,
num_scales,
in_channels,
out_channels,
conv_cfg=None,
norm_cfg=dict(type='BN', requires_grad=True),
act_cfg=dict(type='LeakyReLU', negative_slope=0.1),
init_cfg=None):
super(YOLOV3Neck, self).__init__(init_cfg)
assert (num_scales == len(in_channels) == len(out_channels))
self.num_scales = num_scales
self.in_channels = in_channels
self.out_channels = out_channels
# shortcut
cfg = dict(conv_cfg=conv_cfg, norm_cfg=norm_cfg, act_cfg=act_cfg)
# To support arbitrary scales, the code looks awful, but it works.
# Better solution is welcomed.
self.detect1 = DetectionBlock(in_channels[0], out_channels[0], **cfg)
for i in range(1, self.num_scales):
in_c, out_c = self.in_channels[i], self.out_channels[i]
inter_c = out_channels[i - 1]
self.add_module(f'conv{i}', ConvModule(inter_c, out_c, 1, **cfg))
# in_c + out_c : High-lvl feats will be cat with low-lvl feats
self.add_module(f'detect{i+1}',
DetectionBlock(in_c + out_c, out_c, **cfg))
def forward(self, feats):
assert len(feats) == self.num_scales
# processed from bottom (high-lvl) to top (low-lvl)
outs = []
out = self.detect1(feats[-1])
outs.append(out)
for i, x in enumerate(reversed(feats[:-1])):
conv = getattr(self, f'conv{i+1}')
tmp = conv(out)
# Cat with low-lvl feats
tmp = F.interpolate(tmp, scale_factor=2)
tmp = torch.cat((tmp, x), 1)
detect = getattr(self, f'detect{i+2}')
out = detect(tmp)
outs.append(out)
return tuple(outs)