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import mmcv
import torch.nn as nn
from ..builder import LOSSES
from .utils import weighted_loss
@mmcv.jit(derivate=True, coderize=True)
@weighted_loss
def gaussian_focal_loss(pred, gaussian_target, alpha=2.0, gamma=4.0):
"""`Focal Loss <https://arxiv.org/abs/1708.02002>`_ for targets in gaussian
distribution.
Args:
pred (torch.Tensor): The prediction.
gaussian_target (torch.Tensor): The learning target of the prediction
in gaussian distribution.
alpha (float, optional): A balanced form for Focal Loss.
Defaults to 2.0.
gamma (float, optional): The gamma for calculating the modulating
factor. Defaults to 4.0.
"""
eps = 1e-12
pos_weights = gaussian_target.eq(1)
neg_weights = (1 - gaussian_target).pow(gamma)
pos_loss = -(pred + eps).log() * (1 - pred).pow(alpha) * pos_weights
neg_loss = -(1 - pred + eps).log() * pred.pow(alpha) * neg_weights
return pos_loss + neg_loss
@LOSSES.register_module()
class GaussianFocalLoss(nn.Module):
"""GaussianFocalLoss is a variant of focal loss.
More details can be found in the `paper
<https://arxiv.org/abs/1808.01244>`_
Code is modified from `kp_utils.py
<https://github.com/princeton-vl/CornerNet/blob/master/models/py_utils/kp_utils.py#L152>`_ # noqa: E501
Please notice that the target in GaussianFocalLoss is a gaussian heatmap,
not 0/1 binary target.
Args:
alpha (float): Power of prediction.
gamma (float): Power of target for negative samples.
reduction (str): Options are "none", "mean" and "sum".
loss_weight (float): Loss weight of current loss.
"""
def __init__(self,
alpha=2.0,
gamma=4.0,
reduction='mean',
loss_weight=1.0):
super(GaussianFocalLoss, self).__init__()
self.alpha = alpha
self.gamma = gamma
self.reduction = reduction
self.loss_weight = loss_weight
def forward(self,
pred,
target,
weight=None,
avg_factor=None,
reduction_override=None):
"""Forward function.
Args:
pred (torch.Tensor): The prediction.
target (torch.Tensor): The learning target of the prediction
in gaussian distribution.
weight (torch.Tensor, optional): The weight of loss for each
prediction. Defaults to None.
avg_factor (int, optional): Average factor that is used to average
the loss. Defaults to None.
reduction_override (str, optional): The reduction method used to
override the original reduction method of the loss.
Defaults to None.
"""
assert reduction_override in (None, 'none', 'mean', 'sum')
reduction = (
reduction_override if reduction_override else self.reduction)
loss_reg = self.loss_weight * gaussian_focal_loss(
pred,
target,
weight,
alpha=self.alpha,
gamma=self.gamma,
reduction=reduction,
avg_factor=avg_factor)
return loss_reg
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