import os import torch import torch.nn as nn import torch.nn.functional as F from utils.general import xywh2xyxy from utils.metrics import bbox_iou from utils.tal.anchor_generator import dist2bbox, make_anchors, bbox2dist from utils.tal.assigner import TaskAlignedAssigner from utils.torch_utils import de_parallel def smooth_BCE(eps=0.1): # https://github.com/ultralytics/yolov3/issues/238#issuecomment-598028441 # return positive, negative label smoothing BCE targets return 1.0 - 0.5 * eps, 0.5 * eps 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 FocalLoss(nn.Module): # Wraps focal loss around existing loss_fcn(), i.e. criteria = FocalLoss(nn.BCEWithLogitsLoss(), gamma=1.5) def __init__(self, loss_fcn, gamma=1.5, alpha=0.25): super().__init__() self.loss_fcn = loss_fcn # must be nn.BCEWithLogitsLoss() self.gamma = gamma self.alpha = alpha self.reduction = loss_fcn.reduction self.loss_fcn.reduction = "none" # required to apply FL to each element def forward(self, pred, true): loss = self.loss_fcn(pred, true) # p_t = torch.exp(-loss) # loss *= self.alpha * (1.000001 - p_t) ** self.gamma # non-zero power for gradient stability # TF implementation https://github.com/tensorflow/addons/blob/v0.7.1/tensorflow_addons/losses/focal_loss.py pred_prob = torch.sigmoid(pred) # prob from logits p_t = true * pred_prob + (1 - true) * (1 - pred_prob) alpha_factor = true * self.alpha + (1 - true) * (1 - self.alpha) modulating_factor = (1.0 - p_t) ** self.gamma loss *= alpha_factor * modulating_factor if self.reduction == "mean": return loss.mean() elif self.reduction == "sum": return loss.sum() else: # 'none' 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 bbox_mask = fg_mask.unsqueeze(-1).repeat([1, 1, 4]) # (b, h*w, 4) pred_bboxes_pos = torch.masked_select(pred_bboxes, bbox_mask).view(-1, 4) target_bboxes_pos = torch.masked_select(target_bboxes, bbox_mask).view(-1, 4) bbox_weight = torch.masked_select(target_scores.sum(-1), fg_mask).unsqueeze(-1) iou = bbox_iou(pred_bboxes_pos, target_bboxes_pos, xywh=False, CIoU=True) loss_iou = 1.0 - iou loss_iou *= bbox_weight loss_iou = loss_iou.sum() / target_scores_sum # dfl loss if self.use_dfl: dist_mask = fg_mask.unsqueeze(-1).repeat([1, 1, (self.reg_max + 1) * 4]) pred_dist_pos = torch.masked_select(pred_dist, dist_mask).view(-1, 4, self.reg_max + 1) target_ltrb = bbox2dist(anchor_points, target_bboxes, self.reg_max) target_ltrb_pos = torch.masked_select(target_ltrb, bbox_mask).view(-1, 4) loss_dfl = self._df_loss(pred_dist_pos, target_ltrb_pos) * bbox_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, iou def _df_loss(self, pred_dist, target): target_left = target.to(torch.long) target_right = target_left + 1 weight_left = target_right.to(torch.float) - target weight_right = 1 - weight_left loss_left = F.cross_entropy(pred_dist.view(-1, self.reg_max + 1), target_left.view(-1), reduction="none").view( target_left.shape) * weight_left loss_right = F.cross_entropy(pred_dist.view(-1, self.reg_max + 1), target_right.view(-1), reduction="none").view(target_left.shape) * weight_right return (loss_left + loss_right).mean(-1, keepdim=True) class ComputeLoss: # Compute losses def __init__(self, model, use_dfl=True): device = next(model.parameters()).device # get model device h = model.hyp # hyperparameters # Define criteria BCEcls = nn.BCEWithLogitsLoss(pos_weight=torch.tensor([h["cls_pw"]], device=device), reduction='none') # Class label smoothing https://arxiv.org/pdf/1902.04103.pdf eqn 3 self.cp, self.cn = smooth_BCE(eps=h.get("label_smoothing", 0.0)) # positive, negative BCE targets # Focal loss g = h["fl_gamma"] # focal loss gamma if g > 0: BCEcls = FocalLoss(BCEcls, g) m = de_parallel(model).model[-1] # Detect() module self.balance = {3: [4.0, 1.0, 0.4]}.get(m.nl, [4.0, 1.0, 0.25, 0.06, 0.02]) # P3-P7 self.BCEcls = BCEcls self.hyp = h self.stride = m.stride # model strides self.nc = m.nc # number of classes self.nl = m.nl # number of layers self.no = m.no self.reg_max = m.reg_max self.device = device self.assigner = TaskAlignedAssigner(topk=int(os.getenv('YOLOM', 10)), num_classes=self.nc, alpha=float(os.getenv('YOLOA', 0.5)), beta=float(os.getenv('YOLOB', 6.0))) self.bbox_loss = BboxLoss(m.reg_max - 1, use_dfl=use_dfl).to(device) self.proj = torch.arange(m.reg_max).float().to(device) # / 120.0 self.use_dfl = use_dfl def preprocess(self, targets, batch_size, scale_tensor): if targets.shape[0] == 0: out = torch.zeros(batch_size, 0, 5, device=self.device) else: i = targets[:, 0] # image index _, counts = i.unique(return_counts=True) out = torch.zeros(batch_size, counts.max(), 5, device=self.device) for j in range(batch_size): matches = i == j n = matches.sum() if n: out[j, :n] = targets[matches, 1:] out[..., 1:5] = xywh2xyxy(out[..., 1:5].mul_(scale_tensor)) return out def bbox_decode(self, anchor_points, pred_dist): if self.use_dfl: b, a, c = pred_dist.shape # batch, anchors, channels pred_dist = pred_dist.view(b, a, 4, c // 4).softmax(3).matmul(self.proj.type(pred_dist.dtype)) # pred_dist = pred_dist.view(b, a, c // 4, 4).transpose(2,3).softmax(3).matmul(self.proj.type(pred_dist.dtype)) # pred_dist = (pred_dist.view(b, a, c // 4, 4).softmax(2) * self.proj.type(pred_dist.dtype).view(1, 1, -1, 1)).sum(2) return dist2bbox(pred_dist, anchor_points, xywh=False) def __call__(self, p, targets, img=None, epoch=0): loss = torch.zeros(3, device=self.device) # box, cls, dfl feats = p[1] if isinstance(p, tuple) else p pred_distri, pred_scores = torch.cat([xi.view(feats[0].shape[0], self.no, -1) for xi in feats], 2).split( (self.reg_max * 4, self.nc), 1) pred_scores = pred_scores.permute(0, 2, 1).contiguous() pred_distri = pred_distri.permute(0, 2, 1).contiguous() dtype = pred_scores.dtype batch_size, grid_size = pred_scores.shape[:2] imgsz = torch.tensor(feats[0].shape[2:], device=self.device, dtype=dtype) * self.stride[0] # image size (h,w) anchor_points, stride_tensor = make_anchors(feats, self.stride, 0.5) # targets targets = self.preprocess(targets, batch_size, scale_tensor=imgsz[[1, 0, 1, 0]]) gt_labels, gt_bboxes = targets.split((1, 4), 2) # cls, xyxy mask_gt = gt_bboxes.sum(2, keepdim=True).gt_(0) # pboxes pred_bboxes = self.bbox_decode(anchor_points, pred_distri) # xyxy, (b, h*w, 4) target_labels, target_bboxes, target_scores, fg_mask = self.assigner( pred_scores.detach().sigmoid(), (pred_bboxes.detach() * stride_tensor).type(gt_bboxes.dtype), anchor_points * stride_tensor, gt_labels, gt_bboxes, mask_gt) target_bboxes /= stride_tensor target_scores_sum = max(target_scores.sum(), 1) # cls loss # loss[1] = self.varifocal_loss(pred_scores, target_scores, target_labels) / target_scores_sum # VFL way loss[1] = self.BCEcls(pred_scores, target_scores.to(dtype)).sum() / target_scores_sum # BCE # bbox loss if fg_mask.sum(): loss[0], loss[2], iou = self.bbox_loss(pred_distri, pred_bboxes, anchor_points, target_bboxes, target_scores, target_scores_sum, fg_mask) loss[0] *= 7.5 # box gain loss[1] *= 0.5 # cls gain loss[2] *= 1.5 # dfl gain return loss.sum() * batch_size, loss.detach() # loss(box, cls, dfl)