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"""Convolutional attention block."""
import attr
import torch
from torch import nn, Tensor
import torch.nn.functional as F
from text_recognizer.networks.vqvae.norm import Normalize
@attr.s(eq=False)
class Attention(nn.Module):
"""Convolutional attention."""
in_channels: int = attr.ib()
q: nn.Conv2d = attr.ib(init=False)
k: nn.Conv2d = attr.ib(init=False)
v: nn.Conv2d = attr.ib(init=False)
proj: nn.Conv2d = attr.ib(init=False)
norm: Normalize = attr.ib(init=False)
def __attrs_post_init__(self) -> None:
"""Post init configuration."""
super().__init__()
self.q = nn.Conv2d(
in_channels=self.in_channels,
out_channels=self.in_channels,
kernel_size=1,
stride=1,
padding=0,
)
self.k = nn.Conv2d(
in_channels=self.in_channels,
out_channels=self.in_channels,
kernel_size=1,
stride=1,
padding=0,
)
self.v = nn.Conv2d(
in_channels=self.in_channels,
out_channels=self.in_channels,
kernel_size=1,
stride=1,
padding=0,
)
self.norm = Normalize(num_channels=self.in_channels)
self.proj = nn.Conv2d(
in_channels=self.in_channels,
out_channels=self.in_channels,
kernel_size=1,
stride=1,
padding=0,
)
def forward(self, x: Tensor) -> Tensor:
"""Applies attention to feature maps."""
residual = x
x = self.norm(x)
q = self.q(x)
k = self.k(x)
v = self.v(x)
# Attention
B, C, H, W = q.shape
q = q.reshape(B, C, H * W).permute(0, 2, 1) # [B, HW, C]
k = k.reshape(B, C, H * W) # [B, C, HW]
energy = torch.bmm(q, k) * (int(C) ** -0.5)
attention = F.softmax(energy, dim=2)
# Compute attention to which values
v = v.reshape(B, C, H * W)
attention = attention.permute(0, 2, 1) # [B, HW, HW]
out = torch.bmm(v, attention)
out = out.reshape(B, C, H, W)
out = self.proj(out)
return out + residual
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