CoordConv.py

import torch
import torch.nn as nn


class AddCoordsTh(nn.Module):
    def __init__(self, x_dim=64, y_dim=64, with_r=False):
        super(AddCoordsTh, self).__init__()
        self.x_dim = x_dim
        self.y_dim = y_dim
        self.with_r = with_r

    def forward(self, input_tensor):
        """
        input_tensor: (batch, c, x_dim, y_dim)
        """
        batch_size_tensor = input_tensor.shape[0]

        xx_ones = torch.ones([1, self.y_dim], dtype=torch.int32)
        xx_ones = xx_ones.unsqueeze(-1)

        xx_range = torch.arange(self.x_dim, dtype=torch.int32).unsqueeze(0)
        xx_range = xx_range.unsqueeze(1)

        xx_channel = torch.matmul(xx_ones, xx_range)
        xx_channel = xx_channel.unsqueeze(-1)

        yy_ones = torch.ones([1, self.x_dim], dtype=torch.int32)
        yy_ones = yy_ones.unsqueeze(1)

        yy_range = torch.arange(self.y_dim, dtype=torch.int32).unsqueeze(0)
        yy_range = yy_range.unsqueeze(-1)

        yy_channel = torch.matmul(yy_range, yy_ones)
        yy_channel = yy_channel.unsqueeze(-1)

        xx_channel = xx_channel.permute(0, 3, 2, 1)
        yy_channel = yy_channel.permute(0, 3, 2, 1)

        xx_channel = xx_channel.float() / (self.x_dim - 1)
        yy_channel = yy_channel.float() / (self.y_dim - 1)

        xx_channel = xx_channel * 2 - 1
        yy_channel = yy_channel * 2 - 1

        xx_channel = xx_channel.repeat(batch_size_tensor, 1, 1, 1)
        yy_channel = yy_channel.repeat(batch_size_tensor, 1, 1, 1)

        ret = torch.cat([input_tensor, xx_channel, yy_channel], dim=1)

        if self.with_r:
            rr = torch.sqrt(torch.pow(xx_channel - 0.5, 2) + torch.pow(yy_channel - 0.5, 2))
            ret = torch.cat([ret, rr], dim=1)

        return ret


class CoordConvTh(nn.Module):
    """CoordConv layer as in the paper."""
    def __init__(self, x_dim, y_dim, with_r, *args, **kwargs):
        super(CoordConvTh, self).__init__()
        self.addcoords = AddCoordsTh(x_dim=x_dim, y_dim=y_dim, with_r=with_r)
        self.conv = nn.Conv2d(*args, **kwargs)

    def forward(self, input_tensor):
        ret = self.addcoords(input_tensor)
        ret = self.conv(ret)
        return ret


'''
An alternative implementation for PyTorch with auto-infering the x-y dimensions.
'''
class AddCoords(nn.Module):

    def __init__(self, with_r=False):
        super().__init__()
        self.with_r = with_r

    def forward(self, input_tensor):
        """
        Args:
            input_tensor: shape(batch, channel, x_dim, y_dim)
        """
        batch_size, _, x_dim, y_dim = input_tensor.size()

        xx_channel = torch.arange(x_dim).repeat(1, y_dim, 1)
        yy_channel = torch.arange(y_dim).repeat(1, x_dim, 1).transpose(1, 2)

        xx_channel = xx_channel.float() / (x_dim - 1)
        yy_channel = yy_channel.float() / (y_dim - 1)

        xx_channel = xx_channel * 2 - 1
        yy_channel = yy_channel * 2 - 1

        xx_channel = xx_channel.repeat(batch_size, 1, 1, 1).transpose(2, 3)
        yy_channel = yy_channel.repeat(batch_size, 1, 1, 1).transpose(2, 3)

        ret = torch.cat([
            input_tensor,
            xx_channel.type_as(input_tensor),
            yy_channel.type_as(input_tensor)], dim=1)

        if self.with_r:
            rr = torch.sqrt(torch.pow(xx_channel.type_as(input_tensor) - 0.5, 2) + torch.pow(yy_channel.type_as(input_tensor) - 0.5, 2))
            ret = torch.cat([ret, rr], dim=1)

        return ret


class CoordConv(nn.Module):

    def __init__(self, in_channels, out_channels, with_r=False, **kwargs):
        super().__init__()
        self.addcoords = AddCoords(with_r=with_r)
        in_size = in_channels+2
        if with_r:
            in_size += 1
        self.conv = nn.Conv2d(in_size, out_channels, **kwargs)

    def forward(self, x):
        ret = self.addcoords(x)
        ret = self.conv(ret)
        return ret