【mmdetection】FPN模块的构建源码

import torch.nn as nn
import torch.nn.functional as F
from mmcv.cnn import xavier_init
from mmdet.core import auto_fp16
from ..registry import NECKS
from ..utils import ConvModule
@NECKS.register_module
class FPN(nn.Module):
    """
    Feature Pyramid Network.
    This is an implementation of - Feature Pyramid Networks for Object
    Detection (https://arxiv.org/abs/1612.03144)
    Args:
        in_channels (List[int]):
            number of input channels per scale
            # 不同尺度的feature map输入FPN的channel数
        out_channels (int):
            number of output channels (used at each scale)
            # 经过FPN后不同尺度的feature map输出的channel数（默认为２５１）
        num_outs (int):
            number of output scales
            # 
        start_level (int):
            index of the first input scale to use as an output scale
        end_level (int, default=-1):
            index of the last input scale to use as an output scale