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import torch
import torch.nn as nn
import torch.nn.functional as F
from .utils import weight_reduce_loss
def cross_entropy(pred,
label,
weight=None,
reduction='mean',
avg_factor=None,
class_weight=None,
ignore_index=-100):
"""Calculate the CrossEntropy loss.
Args:
pred (torch.Tensor): The prediction with shape (N, C), C is the number
of classes.
label (torch.Tensor): The learning label of the prediction.
weight (torch.Tensor, optional): Sample-wise loss weight.
reduction (str, optional): The method used to reduce the loss.
avg_factor (int, optional): Average factor that is used to average
the loss. Defaults to None.
class_weight (list[float], optional): The weight for each class.
ignore_index (int | None): The label index to be ignored.
If None, it will be set to default value. Default: -100.
Returns:
torch.Tensor: The calculated loss
"""
# The default value of ignore_index is the same as F.cross_entropy
ignore_index = -100 if ignore_index is None else ignore_index
# element-wise losses
loss = F.cross_entropy(pred,
label,
weight=class_weight,
reduction='none',
ignore_index=ignore_index)
# apply weights and do the reduction
if weight is not None:
weight = weight.float()
loss = weight_reduce_loss(loss,
weight=weight,
reduction=reduction,
avg_factor=avg_factor)
return loss
def _expand_onehot_labels(labels, label_weights, label_channels, ignore_index):
"""Expand onehot labels to match the size of prediction."""
bin_labels = labels.new_full((labels.size(0), label_channels), 0)
valid_mask = (labels >= 0) & (labels != ignore_index)
inds = torch.nonzero(valid_mask & (labels < label_channels),
as_tuple=False)
if inds.numel() > 0:
bin_labels[inds, labels[inds]] = 1
valid_mask = valid_mask.view(-1, 1).expand(labels.size(0),
label_channels).float()
if label_weights is None:
bin_label_weights = valid_mask
else:
bin_label_weights = label_weights.view(-1, 1).repeat(1, label_channels)
bin_label_weights *= valid_mask
return bin_labels, bin_label_weights
def binary_cross_entropy(pred,
label,
weight=None,
reduction='mean',
avg_factor=None,
class_weight=None,
ignore_index=-100):
"""Calculate the binary CrossEntropy loss.
Args:
pred (torch.Tensor): The prediction with shape (N, 1).
label (torch.Tensor): The learning label of the prediction.
weight (torch.Tensor, optional): Sample-wise loss weight.
reduction (str, optional): The method used to reduce the loss.
Options are "none", "mean" and "sum".
avg_factor (int, optional): Average factor that is used to average
the loss. Defaults to None.
class_weight (list[float], optional): The weight for each class.
ignore_index (int | None): The label index to be ignored.
If None, it will be set to default value. Default: -100.
Returns:
torch.Tensor: The calculated loss.
"""
# The default value of ignore_index is the same as F.cross_entropy
ignore_index = -100 if ignore_index is None else ignore_index
if pred.dim() != label.dim():
label, weight = _expand_onehot_labels(label, weight, pred.size(-1),
ignore_index)
# weighted element-wise losses
if weight is not None:
weight = weight.float()
loss = F.binary_cross_entropy_with_logits(pred,
label.float(),
pos_weight=class_weight,
reduction='none')
# do the reduction for the weighted loss
loss = weight_reduce_loss(loss,
weight,
reduction=reduction,
avg_factor=avg_factor)
return loss
def mask_cross_entropy(pred,
target,
label,
reduction='mean',
avg_factor=None,
class_weight=None,
ignore_index=None):
"""Calculate the CrossEntropy loss for masks.
Args:
pred (torch.Tensor): The prediction with shape (N, C, *), C is the
number of classes. The trailing * indicates arbitrary shape.
target (torch.Tensor): The learning label of the prediction.
label (torch.Tensor): ``label`` indicates the class label of the mask
corresponding object. This will be used to select the mask in the
of the class which the object belongs to when the mask prediction
if not class-agnostic.
reduction (str, optional): The method used to reduce the loss.
Options are "none", "mean" and "sum".
avg_factor (int, optional): Average factor that is used to average
the loss. Defaults to None.
class_weight (list[float], optional): The weight for each class.
ignore_index (None): Placeholder, to be consistent with other loss.
Default: None.
Returns:
torch.Tensor: The calculated loss
Example:
>>> N, C = 3, 11
>>> H, W = 2, 2
>>> pred = torch.randn(N, C, H, W) * 1000
>>> target = torch.rand(N, H, W)
>>> label = torch.randint(0, C, size=(N,))
>>> reduction = 'mean'
>>> avg_factor = None
>>> class_weights = None
>>> loss = mask_cross_entropy(pred, target, label, reduction,
>>> avg_factor, class_weights)
>>> assert loss.shape == (1,)
"""
assert ignore_index is None, 'BCE loss does not support ignore_index'
# TODO: handle these two reserved arguments
assert reduction == 'mean' and avg_factor is None
num_rois = pred.size()[0]
inds = torch.arange(0, num_rois, dtype=torch.long, device=pred.device)
pred_slice = pred[inds, label].squeeze(1)
return F.binary_cross_entropy_with_logits(pred_slice,
target,
weight=class_weight,
reduction='mean')[None]
class CrossEntropyLoss(nn.Module):
def __init__(self,
use_sigmoid=False,
use_mask=False,
reduction='mean',
class_weight=None,
ignore_index=None,
loss_weight=1.0):
"""CrossEntropyLoss.
Args:
use_sigmoid (bool, optional): Whether the prediction uses sigmoid
of softmax. Defaults to False.
use_mask (bool, optional): Whether to use mask cross entropy loss.
Defaults to False.
reduction (str, optional): . Defaults to 'mean'.
Options are "none", "mean" and "sum".
class_weight (list[float], optional): Weight of each class.
Defaults to None.
ignore_index (int | None): The label index to be ignored.
Defaults to None.
loss_weight (float, optional): Weight of the loss. Defaults to 1.0.
"""
super(CrossEntropyLoss, self).__init__()
assert (use_sigmoid is False) or (use_mask is False)
self.use_sigmoid = use_sigmoid
self.use_mask = use_mask
self.reduction = reduction
self.loss_weight = loss_weight
self.class_weight = class_weight
self.ignore_index = ignore_index
if self.use_sigmoid:
self.cls_criterion = binary_cross_entropy
elif self.use_mask:
self.cls_criterion = mask_cross_entropy
else:
self.cls_criterion = cross_entropy
def forward(self,
cls_score,
label,
weight=None,
avg_factor=None,
reduction_override=None,
ignore_index=None,
**kwargs):
"""Forward function.
Args:
cls_score (torch.Tensor): The prediction.
label (torch.Tensor): The learning label of the prediction.
weight (torch.Tensor, optional): Sample-wise loss weight.
avg_factor (int, optional): Average factor that is used to average
the loss. Defaults to None.
reduction_override (str, optional): The method used to reduce the
loss. Options are "none", "mean" and "sum".
ignore_index (int | None): The label index to be ignored.
If not None, it will override the default value. Default: None.
Returns:
torch.Tensor: The calculated loss.
"""
assert reduction_override in (None, 'none', 'mean', 'sum')
reduction = (reduction_override
if reduction_override else self.reduction)
if ignore_index is None:
ignore_index = self.ignore_index
if self.class_weight is not None:
class_weight = cls_score.new_tensor(self.class_weight,
device=cls_score.device)
else:
class_weight = None
loss_cls = self.loss_weight * self.cls_criterion(
cls_score,
label,
weight,
class_weight=class_weight,
reduction=reduction,
avg_factor=avg_factor,
ignore_index=ignore_index,
**kwargs)
return loss_cls
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