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"""Modified from https://github.com/LikeLy-Journey/SegmenTron/blob/master/
segmentron/solver/loss.py (Apache-2.0 License)"""
import torch
import torch.nn as nn
import torch.nn.functional as F
from ..builder import LOSSES
from .utils import get_class_weight, weighted_loss
@weighted_loss
def dice_loss(pred,
target,
valid_mask,
smooth=1,
exponent=2,
class_weight=None,
ignore_index=255):
assert pred.shape[0] == target.shape[0]
total_loss = 0
num_classes = pred.shape[1]
for i in range(num_classes):
if i != ignore_index:
dice_loss = binary_dice_loss(
pred[:, i],
target[..., i],
valid_mask=valid_mask,
smooth=smooth,
exponent=exponent)
if class_weight is not None:
dice_loss *= class_weight[i]
total_loss += dice_loss
return total_loss / num_classes
@weighted_loss
def binary_dice_loss(pred, target, valid_mask, smooth=1, exponent=2, **kwards):
assert pred.shape[0] == target.shape[0]
pred = pred.reshape(pred.shape[0], -1)
target = target.reshape(target.shape[0], -1)
valid_mask = valid_mask.reshape(valid_mask.shape[0], -1)
num = torch.sum(torch.mul(pred, target) * valid_mask, dim=1) * 2 + smooth
den = torch.sum(pred.pow(exponent) + target.pow(exponent), dim=1) + smooth
return 1 - num / den
@LOSSES.register_module()
class DiceLoss(nn.Module):
"""DiceLoss.
This loss is proposed in `V-Net: Fully Convolutional Neural Networks for
Volumetric Medical Image Segmentation <https://arxiv.org/abs/1606.04797>`_.
Args:
loss_type (str, optional): Binary or multi-class loss.
Default: 'multi_class'. Options are "binary" and "multi_class".
smooth (float): A float number to smooth loss, and avoid NaN error.
Default: 1
exponent (float): An float number to calculate denominator
value: \\sum{x^exponent} + \\sum{y^exponent}. Default: 2.
reduction (str, optional): The method used to reduce the loss. Options
are "none", "mean" and "sum". This parameter only works when
per_image is True. Default: 'mean'.
class_weight (list[float] | str, optional): Weight of each class. If in
str format, read them from a file. Defaults to None.
loss_weight (float, optional): Weight of the loss. Default to 1.0.
ignore_index (int | None): The label index to be ignored. Default: 255.
"""
def __init__(self,
smooth=1,
exponent=2,
reduction='mean',
class_weight=None,
loss_weight=1.0,
ignore_index=255,
**kwards):
super(DiceLoss, self).__init__()
self.smooth = smooth
self.exponent = exponent
self.reduction = reduction
self.class_weight = get_class_weight(class_weight)
self.loss_weight = loss_weight
self.ignore_index = ignore_index
def forward(self,
pred,
target,
avg_factor=None,
reduction_override=None,
**kwards):
assert reduction_override in (None, 'none', 'mean', 'sum')
reduction = (
reduction_override if reduction_override else self.reduction)
if self.class_weight is not None:
class_weight = pred.new_tensor(self.class_weight)
else:
class_weight = None
pred = F.softmax(pred, dim=1)
num_classes = pred.shape[1]
one_hot_target = F.one_hot(
torch.clamp(target.long(), 0, num_classes - 1),
num_classes=num_classes)
valid_mask = (target != self.ignore_index).long()
loss = self.loss_weight * dice_loss(
pred,
one_hot_target,
valid_mask=valid_mask,
reduction=reduction,
avg_factor=avg_factor,
smooth=self.smooth,
exponent=self.exponent,
class_weight=class_weight,
ignore_index=self.ignore_index)
return loss
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