opendet/modeling/heads/db_head.py

import torch
from torch import nn
import torch.nn.functional as F


class Head(nn.Module):

    def __init__(self, in_channels, kernel_list=[3, 2, 2], **kwargs):
        super(Head, self).__init__()

        self.conv1 = nn.Conv2d(
            in_channels=in_channels,
            out_channels=in_channels // 4,
            kernel_size=kernel_list[0],
            padding=int(kernel_list[0] // 2),
            bias=False,
        )
        self.conv_bn1 = nn.BatchNorm2d(num_features=in_channels // 4, )

        self.conv2 = nn.ConvTranspose2d(
            in_channels=in_channels // 4,
            out_channels=in_channels // 4,
            kernel_size=kernel_list[1],
            stride=2,
        )
        self.conv_bn2 = nn.BatchNorm2d(num_features=in_channels // 4, )
        self.conv3 = nn.ConvTranspose2d(
            in_channels=in_channels // 4,
            out_channels=1,
            kernel_size=kernel_list[2],
            stride=2,
        )

    def forward(self, x, return_f=False):
        x = self.conv1(x)
        x = F.relu(self.conv_bn1(x))
        x = self.conv2(x)
        x = F.relu(self.conv_bn2(x))
        if return_f is True:
            f = x
        x = self.conv3(x)
        x = torch.sigmoid(x)
        if return_f is True:
            return x, f
        return x


class DBHead(nn.Module):
    """
    Differentiable Binarization (DB) for text detection:
        see https://arxiv.org/abs/1911.08947
    args:
        params(dict): super parameters for build DB network
    """

    def __init__(self, in_channels, k=50, **kwargs):
        super(DBHead, self).__init__()
        self.k = k
        self.binarize = Head(in_channels, **kwargs)
        self.thresh = Head(in_channels, **kwargs)

    def step_function(self, x, y):
        return torch.reciprocal(1 + torch.exp(-self.k * (x - y)))

    def forward(self, x, data=None):
        shrink_maps = self.binarize(x)
        if not self.training:
            return {'maps': shrink_maps}

        threshold_maps = self.thresh(x)
        binary_maps = self.step_function(shrink_maps, threshold_maps)
        y = torch.concat([shrink_maps, threshold_maps, binary_maps], dim=1)
        return {'maps': y}