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import torch
import torch.nn as nn
import torch.nn.functional as F
from ..builder import LOSSES
def _expand_onehot_labels(labels, label_weights, label_channels):
bin_labels = labels.new_full((labels.size(0), label_channels), 0)
inds = torch.nonzero(
(labels >= 0) & (labels < label_channels), as_tuple=False).squeeze()
if inds.numel() > 0:
bin_labels[inds, labels[inds]] = 1
bin_label_weights = label_weights.view(-1, 1).expand(
label_weights.size(0), label_channels)
return bin_labels, bin_label_weights
# TODO: code refactoring to make it consistent with other losses
@LOSSES.register_module()
class GHMC(nn.Module):
"""GHM Classification Loss.
Details of the theorem can be viewed in the paper
`Gradient Harmonized Single-stage Detector
<https://arxiv.org/abs/1811.05181>`_.
Args:
bins (int): Number of the unit regions for distribution calculation.
momentum (float): The parameter for moving average.
use_sigmoid (bool): Can only be true for BCE based loss now.
loss_weight (float): The weight of the total GHM-C loss.
"""
def __init__(self, bins=10, momentum=0, use_sigmoid=True, loss_weight=1.0):
super(GHMC, self).__init__()
self.bins = bins
self.momentum = momentum
edges = torch.arange(bins + 1).float() / bins
self.register_buffer('edges', edges)
self.edges[-1] += 1e-6
if momentum > 0:
acc_sum = torch.zeros(bins)
self.register_buffer('acc_sum', acc_sum)
self.use_sigmoid = use_sigmoid
if not self.use_sigmoid:
raise NotImplementedError
self.loss_weight = loss_weight
def forward(self, pred, target, label_weight, *args, **kwargs):
"""Calculate the GHM-C loss.
Args:
pred (float tensor of size [batch_num, class_num]):
The direct prediction of classification fc layer.
target (float tensor of size [batch_num, class_num]):
Binary class target for each sample.
label_weight (float tensor of size [batch_num, class_num]):
the value is 1 if the sample is valid and 0 if ignored.
Returns:
The gradient harmonized loss.
"""
# the target should be binary class label
if pred.dim() != target.dim():
target, label_weight = _expand_onehot_labels(
target, label_weight, pred.size(-1))
target, label_weight = target.float(), label_weight.float()
edges = self.edges
mmt = self.momentum
weights = torch.zeros_like(pred)
# gradient length
g = torch.abs(pred.sigmoid().detach() - target)
valid = label_weight > 0
tot = max(valid.float().sum().item(), 1.0)
n = 0 # n valid bins
for i in range(self.bins):
inds = (g >= edges[i]) & (g < edges[i + 1]) & valid
num_in_bin = inds.sum().item()
if num_in_bin > 0:
if mmt > 0:
self.acc_sum[i] = mmt * self.acc_sum[i] \
+ (1 - mmt) * num_in_bin
weights[inds] = tot / self.acc_sum[i]
else:
weights[inds] = tot / num_in_bin
n += 1
if n > 0:
weights = weights / n
loss = F.binary_cross_entropy_with_logits(
pred, target, weights, reduction='sum') / tot
return loss * self.loss_weight
# TODO: code refactoring to make it consistent with other losses
@LOSSES.register_module()
class GHMR(nn.Module):
"""GHM Regression Loss.
Details of the theorem can be viewed in the paper
`Gradient Harmonized Single-stage Detector
<https://arxiv.org/abs/1811.05181>`_.
Args:
mu (float): The parameter for the Authentic Smooth L1 loss.
bins (int): Number of the unit regions for distribution calculation.
momentum (float): The parameter for moving average.
loss_weight (float): The weight of the total GHM-R loss.
"""
def __init__(self, mu=0.02, bins=10, momentum=0, loss_weight=1.0):
super(GHMR, self).__init__()
self.mu = mu
self.bins = bins
edges = torch.arange(bins + 1).float() / bins
self.register_buffer('edges', edges)
self.edges[-1] = 1e3
self.momentum = momentum
if momentum > 0:
acc_sum = torch.zeros(bins)
self.register_buffer('acc_sum', acc_sum)
self.loss_weight = loss_weight
# TODO: support reduction parameter
def forward(self, pred, target, label_weight, avg_factor=None):
"""Calculate the GHM-R loss.
Args:
pred (float tensor of size [batch_num, 4 (* class_num)]):
The prediction of box regression layer. Channel number can be 4
or 4 * class_num depending on whether it is class-agnostic.
target (float tensor of size [batch_num, 4 (* class_num)]):
The target regression values with the same size of pred.
label_weight (float tensor of size [batch_num, 4 (* class_num)]):
The weight of each sample, 0 if ignored.
Returns:
The gradient harmonized loss.
"""
mu = self.mu
edges = self.edges
mmt = self.momentum
# ASL1 loss
diff = pred - target
loss = torch.sqrt(diff * diff + mu * mu) - mu
# gradient length
g = torch.abs(diff / torch.sqrt(mu * mu + diff * diff)).detach()
weights = torch.zeros_like(g)
valid = label_weight > 0
tot = max(label_weight.float().sum().item(), 1.0)
n = 0 # n: valid bins
for i in range(self.bins):
inds = (g >= edges[i]) & (g < edges[i + 1]) & valid
num_in_bin = inds.sum().item()
if num_in_bin > 0:
n += 1
if mmt > 0:
self.acc_sum[i] = mmt * self.acc_sum[i] \
+ (1 - mmt) * num_in_bin
weights[inds] = tot / self.acc_sum[i]
else:
weights[inds] = tot / num_in_bin
if n > 0:
weights /= n
loss = loss * weights
loss = loss.sum() / tot
return loss * self.loss_weight
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