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# Ultralytics YOLO 🚀, AGPL-3.0 license
import torch
import torch.nn as nn
import torch.nn.functional as F
from .metrics import bbox_iou
from .tal import bbox2dist
class VarifocalLoss(nn.Module):
"""Varifocal loss by Zhang et al. https://arxiv.org/abs/2008.13367."""
def __init__(self):
super().__init__()
def forward(self, pred_score, gt_score, label, alpha=0.75, gamma=2.0):
weight = alpha * pred_score.sigmoid().pow(gamma) * (1 - label) + gt_score * label
with torch.cuda.amp.autocast(enabled=False):
loss = (F.binary_cross_entropy_with_logits(pred_score.float(), gt_score.float(), reduction='none') *
weight).sum()
return loss
class BboxLoss(nn.Module):
def __init__(self, reg_max, use_dfl=False):
super().__init__()
self.reg_max = reg_max
self.use_dfl = use_dfl
def forward(self, pred_dist, pred_bboxes, anchor_points, target_bboxes, target_scores, target_scores_sum, fg_mask):
"""IoU loss."""
weight = torch.masked_select(target_scores.sum(-1), fg_mask).unsqueeze(-1)
iou = bbox_iou(pred_bboxes[fg_mask], target_bboxes[fg_mask], xywh=False, CIoU=True)
loss_iou = ((1.0 - iou) * weight).sum() / target_scores_sum
# DFL loss
if self.use_dfl:
target_ltrb = bbox2dist(anchor_points, target_bboxes, self.reg_max)
loss_dfl = self._df_loss(pred_dist[fg_mask].view(-1, self.reg_max + 1), target_ltrb[fg_mask]) * weight
loss_dfl = loss_dfl.sum() / target_scores_sum
else:
loss_dfl = torch.tensor(0.0).to(pred_dist.device)
return loss_iou, loss_dfl
@staticmethod
def _df_loss(pred_dist, target):
"""Return sum of left and right DFL losses."""
# Distribution Focal Loss (DFL) proposed in Generalized Focal Loss https://ieeexplore.ieee.org/document/9792391
tl = target.long() # target left
tr = tl + 1 # target right
wl = tr - target # weight left
wr = 1 - wl # weight right
return (F.cross_entropy(pred_dist, tl.view(-1), reduction='none').view(tl.shape) * wl +
F.cross_entropy(pred_dist, tr.view(-1), reduction='none').view(tl.shape) * wr).mean(-1, keepdim=True)
class KeypointLoss(nn.Module):
def __init__(self, sigmas) -> None:
super().__init__()
self.sigmas = sigmas
def forward(self, pred_kpts, gt_kpts, kpt_mask, area):
d = (pred_kpts[..., 0] - gt_kpts[..., 0]) ** 2 + (pred_kpts[..., 1] - gt_kpts[..., 1]) ** 2
kpt_loss_factor = (torch.sum(kpt_mask != 0) + torch.sum(kpt_mask == 0)) / (torch.sum(kpt_mask != 0) + 1e-9)
# e = d / (2 * (area * self.sigmas) ** 2 + 1e-9) # from formula
e = d / (2 * self.sigmas) ** 2 / (area + 1e-9) / 2 # from cocoeval
return kpt_loss_factor * ((1 - torch.exp(-e)) * kpt_mask).mean()