# Copyright (c) OpenMMLab. All rights reserved.
import math
import torch
import torch.nn as nn
from torch.autograd import Function
from torch.autograd.function import once_differentiable
from torch.nn.modules.utils import _pair
from ..utils import ext_loader
ext_module = ext_loader.load_ext(
'_ext', ['masked_im2col_forward', 'masked_col2im_forward'])
class MaskedConv2dFunction(Function):
@staticmethod
def symbolic(g, features, mask, weight, bias, padding, stride):
return g.op(
'MMCVMaskedConv2d',
features,
mask,
weight,
bias,
padding=padding,
stride=stride)
@staticmethod
def forward(ctx, features, mask, weight, bias, padding=0, stride=1):
assert mask.dim() == 3 and mask.size(0) == 1
assert features.dim() == 4 and features.size(0) == 1
assert features.size()[2:] == mask.size()[1:]
pad_h, pad_w = _pair(padding)
stride_h, stride_w = _pair(stride)
if stride_h != 1 or stride_w != 1:
raise ValueError(
'Stride could not only be 1 in masked_conv2d currently.')
out_channel, in_channel, kernel_h, kernel_w = weight.size()
batch_size = features.size(0)
out_h = int(
math.floor((features.size(2) + 2 * pad_h -
(kernel_h - 1) - 1) / stride_h + 1))
out_w = int(
math.floor((features.size(3) + 2 * pad_w -
(kernel_h - 1) - 1) / stride_w + 1))
mask_inds = torch.nonzero(mask[0] > 0, as_tuple=False)
output = features.new_zeros(batch_size, out_channel, out_h, out_w)
if mask_inds.numel() > 0:
mask_h_idx = mask_inds[:, 0].contiguous()
mask_w_idx = mask_inds[:, 1].contiguous()
data_col = features.new_zeros(in_channel * kernel_h * kernel_w,
mask_inds.size(0))
ext_module.masked_im2col_forward(
features,
mask_h_idx,
mask_w_idx,
data_col,
kernel_h=kernel_h,
kernel_w=kernel_w,
pad_h=pad_h,
pad_w=pad_w)
masked_output = torch.addmm(1, bias[:, None], 1,
weight.view(out_channel, -1), data_col)
ext_module.masked_col2im_forward(
masked_output,
mask_h_idx,
mask_w_idx,
output,
height=out_h,
width=out_w,
channels=out_channel)
return output
@staticmethod
@once_differentiable
def backward(ctx, grad_output):
return (None, ) * 5
masked_conv2d = MaskedConv2dFunction.apply
[docs]class MaskedConv2d(nn.Conv2d):
"""A MaskedConv2d which inherits the official Conv2d.
The masked forward doesn't implement the backward function and only
supports the stride parameter to be 1 currently.
"""
def __init__(self,
in_channels,
out_channels,
kernel_size,
stride=1,
padding=0,
dilation=1,
groups=1,
bias=True):
super(MaskedConv2d,
self).__init__(in_channels, out_channels, kernel_size, stride,
padding, dilation, groups, bias)
[docs] def forward(self, input, mask=None):
if mask is None: # fallback to the normal Conv2d
return super(MaskedConv2d, self).forward(input)
else:
return masked_conv2d(input, mask, self.weight, self.bias,
self.padding)