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# Original implementation: https://gist.github.com/rwightman/f2d3849281624be7c0f11c85c87c1598
import math
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.nn.modules.utils import _pair, _quadruple
class MedianPool2d(nn.Module):
""" Median pool (usable as median filter when stride=1) module.
Args:
kernel_size: size of pooling kernel, int or 2-tuple
stride: pool stride, int or 2-tuple
padding: pool padding, int or 4-tuple (l, r, t, b) as in pytorch F.pad
same: override padding and enforce same padding, boolean
"""
def __init__(self, kernel_size=3, stride=1, padding=0, same=False):
super(MedianPool2d, self).__init__()
self.k = _pair(kernel_size)
self.stride = _pair(stride)
self.padding = _quadruple(padding) # convert to l, r, t, b
self.same = same
def _padding(self, x):
if self.same:
ih, iw = x.size()[2:]
if ih % self.stride[0] == 0:
ph = max(self.k[0] - self.stride[0], 0)
else:
ph = max(self.k[0] - (ih % self.stride[0]), 0)
if iw % self.stride[1] == 0:
pw = max(self.k[1] - self.stride[1], 0)
else:
pw = max(self.k[1] - (iw % self.stride[1]), 0)
pl = pw // 2
pr = pw - pl
pt = ph // 2
pb = ph - pt
padding = (pl, pr, pt, pb)
else:
padding = self.padding
return padding
def forward(self, x):
# using existing pytorch functions and tensor ops so that we get autograd,
# would likely be more efficient to implement from scratch at C/Cuda level
x = F.pad(x, self._padding(x), mode='reflect')
x = x.unfold(2, self.k[0], self.stride[0]).unfold(3, self.k[1], self.stride[1])
x = x.contiguous().view(x.size()[:4] + (-1,)).median(dim=-1)[0]
return x |