A2注意力机制
A2注意力机制原文为《A2-Nets:Double Attention Networks》,原理就是先使用second-order attention pooling将整幅图的所有关键的特征搜集到了一个集合里,然后用另一种attention机制将这些特征分别图像的每个location。
论文地址:https://arxiv.org/pdf/1810.11579.pdf
代码如下:
import numpy as np
import torch
from torch import nn
from torch.nn import init
from torch.nn import functional as F
class DoubleAttention(nn.Module):
def __init__(self, in_channels,c_m=128,c_n=128,reconstruct = True):
super().__init__()
self.in_channels=in_channels
self.reconstruct = reconstruct
self.c_m=c_m
self.c_n=c_n
self.convA=nn.Conv2d(in_channels,c_m,1)
self.convB=nn.Conv2d(in_channels,c_n,1)
self.convV=nn.Conv2d(in_channels,c_n,1)
if self.reconstruct:
self.conv_reconstruct = nn.Conv2d(c_m, in_channels, kernel_size = 1)
self.init_weights()
def init_weights(self):
for m in self.modules():
if isinstance(m, nn.Conv2d):
init.kaiming_normal_(m.weight, mode='fan_out')
if m.bias is not None:
init.constant_(m.bias, 0)
elif isinstance(m, nn.BatchNorm2d):
init.constant_(m.weight, 1)
init.constant_(m.bias, 0)
elif isinstance(m, nn.Linear):
init.normal_(m.weight, std=0.001)
if m.bias is not None:
init.constant_(m.bias, 0)
def forward(self, x):
b, c, h,w=x.shape
assert c==self.in_channels
A=self.convA(x) #b,c_m,h,w
B=self.convB(x) #b,c_n,h,w
V=self.convV(x) #b,c_n,h,w
tmpA=A.view(b,self.c_m,-1)
attention_maps=F.softmax(B.view(b,self.c_n,-1))
attention_vectors=F.softmax(V.view(b,self.c_n,-1))
# step 1: feature gating
global_descriptors=torch.bmm(tmpA,attention_maps.permute(0,2,1)) #b.c_m,c_n
# step 2: feature distribution
tmpZ = global_descriptors.matmul(attention_vectors) #b,c_m,h*w
tmpZ=tmpZ.view(b,self.c_m,h,w) #b,c_m,h,w
if self.reconstruct:
tmpZ=self.conv_reconstruct(tmpZ)
return tmpZ
if __name__ == '__main__':
input=torch.randn(50,512,7,7)
a2 = DoubleAttention(512)
output=a2(input)
print(output.shape)