# Copyright (c) OpenMMLab. All rights reserved.
import torch
from mmcv.runner import force_fp32
from mmdet.core import bbox_overlaps, multi_apply
from ..builder import HEADS
from .paa_head import PAAHead, levels_to_images
@HEADS.register_module()
class LADHead(PAAHead):
"""Label Assignment Head from the paper: `Improving Object Detection by
Label Assignment Distillation <https://arxiv.org/pdf/2108.10520.pdf>`_"""
@force_fp32(apply_to=('cls_scores', 'bbox_preds', 'iou_preds'))
def get_label_assignment(self,
cls_scores,
bbox_preds,
iou_preds,
gt_bboxes,
gt_labels,
img_metas,
gt_bboxes_ignore=None):
"""Get label assignment (from teacher).
Args:
cls_scores (list[Tensor]): Box scores for each scale level.
Has shape (N, num_anchors * num_classes, H, W)
bbox_preds (list[Tensor]): Box energies / deltas for each scale
level with shape (N, num_anchors * 4, H, W)
iou_preds (list[Tensor]): iou_preds for each scale
level with shape (N, num_anchors * 1, H, W)
gt_bboxes (list[Tensor]): Ground truth bboxes for each image with
shape (num_gts, 4) in [tl_x, tl_y, br_x, br_y] format.
gt_labels (list[Tensor]): class indices corresponding to each box
img_metas (list[dict]): Meta information of each image, e.g.,
image size, scaling factor, etc.
gt_bboxes_ignore (list[Tensor] | None): Specify which bounding
boxes can be ignored when are computing the loss.
Returns:
tuple: Returns a tuple containing label assignment variables.
- labels (Tensor): Labels of all anchors, each with
shape (num_anchors,).
- labels_weight (Tensor): Label weights of all anchor.
each with shape (num_anchors,).
- bboxes_target (Tensor): BBox targets of all anchors.
each with shape (num_anchors, 4).
- bboxes_weight (Tensor): BBox weights of all anchors.
each with shape (num_anchors, 4).
- pos_inds_flatten (Tensor): Contains all index of positive
sample in all anchor.
- pos_anchors (Tensor): Positive anchors.
- num_pos (int): Number of positive anchors.
"""
featmap_sizes = [featmap.size()[-2:] for featmap in cls_scores]
assert len(featmap_sizes) == self.prior_generator.num_levels
device = cls_scores[0].device
anchor_list, valid_flag_list = self.get_anchors(
featmap_sizes, img_metas, device=device)
label_channels = self.cls_out_channels if self.use_sigmoid_cls else 1
cls_reg_targets = self.get_targets(
anchor_list,
valid_flag_list,
gt_bboxes,
img_metas,
gt_bboxes_ignore_list=gt_bboxes_ignore,
gt_labels_list=gt_labels,
label_channels=label_channels,
)
(labels, labels_weight, bboxes_target, bboxes_weight, pos_inds,
pos_gt_index) = cls_reg_targets
cls_scores = levels_to_images(cls_scores)
cls_scores = [
item.reshape(-1, self.cls_out_channels) for item in cls_scores
]
bbox_preds = levels_to_images(bbox_preds)
bbox_preds = [item.reshape(-1, 4) for item in bbox_preds]
pos_losses_list, = multi_apply(self.get_pos_loss, anchor_list,
cls_scores, bbox_preds, labels,
labels_weight, bboxes_target,
bboxes_weight, pos_inds)
with torch.no_grad():
reassign_labels, reassign_label_weight, \
reassign_bbox_weights, num_pos = multi_apply(
self.paa_reassign,
pos_losses_list,
labels,
labels_weight,
bboxes_weight,
pos_inds,
pos_gt_index,
anchor_list)
num_pos = sum(num_pos)
# convert all tensor list to a flatten tensor
labels = torch.cat(reassign_labels, 0).view(-1)
flatten_anchors = torch.cat(
[torch.cat(item, 0) for item in anchor_list])
labels_weight = torch.cat(reassign_label_weight, 0).view(-1)
bboxes_target = torch.cat(bboxes_target,
0).view(-1, bboxes_target[0].size(-1))
pos_inds_flatten = ((labels >= 0)
&
(labels < self.num_classes)).nonzero().reshape(-1)
if num_pos:
pos_anchors = flatten_anchors[pos_inds_flatten]
else:
pos_anchors = None
label_assignment_results = (labels, labels_weight, bboxes_target,
bboxes_weight, pos_inds_flatten,
pos_anchors, num_pos)
return label_assignment_results
def forward_train(self,
x,
label_assignment_results,
img_metas,
gt_bboxes,
gt_labels=None,
gt_bboxes_ignore=None,
**kwargs):
"""Forward train with the available label assignment (student receives
from teacher).
Args:
x (list[Tensor]): Features from FPN.
label_assignment_results (tuple): As the outputs defined in the
function `self.get_label_assignment`.
img_metas (list[dict]): Meta information of each image, e.g.,
image size, scaling factor, etc.
gt_bboxes (Tensor): Ground truth bboxes of the image,
shape (num_gts, 4).
gt_labels (Tensor): Ground truth labels of each box,
shape (num_gts,).
gt_bboxes_ignore (Tensor): Ground truth bboxes to be
ignored, shape (num_ignored_gts, 4).
Returns:
losses: (dict[str, Tensor]): A dictionary of loss components.
"""
outs = self(x)
if gt_labels is None:
loss_inputs = outs + (gt_bboxes, img_metas)
else:
loss_inputs = outs + (gt_bboxes, gt_labels, img_metas)
losses = self.loss(
*loss_inputs,
gt_bboxes_ignore=gt_bboxes_ignore,
label_assignment_results=label_assignment_results)
return losses
@force_fp32(apply_to=('cls_scores', 'bbox_preds', 'iou_preds'))
def loss(self,
cls_scores,
bbox_preds,
iou_preds,
gt_bboxes,
gt_labels,
img_metas,
gt_bboxes_ignore=None,
label_assignment_results=None):
"""Compute losses of the head.
Args:
cls_scores (list[Tensor]): Box scores for each scale level
Has shape (N, num_anchors * num_classes, H, W)
bbox_preds (list[Tensor]): Box energies / deltas for each scale
level with shape (N, num_anchors * 4, H, W)
iou_preds (list[Tensor]): iou_preds for each scale
level with shape (N, num_anchors * 1, H, W)
gt_bboxes (list[Tensor]): Ground truth bboxes for each image with
shape (num_gts, 4) in [tl_x, tl_y, br_x, br_y] format.
gt_labels (list[Tensor]): class indices corresponding to each box
img_metas (list[dict]): Meta information of each image, e.g.,
image size, scaling factor, etc.
gt_bboxes_ignore (list[Tensor] | None): Specify which bounding
boxes can be ignored when are computing the loss.
label_assignment_results (tuple): As the outputs defined in the
function `self.get_label_assignment`.
Returns:
dict[str, Tensor]: A dictionary of loss gmm_assignment.
"""
(labels, labels_weight, bboxes_target, bboxes_weight, pos_inds_flatten,
pos_anchors, num_pos) = label_assignment_results
cls_scores = levels_to_images(cls_scores)
cls_scores = [
item.reshape(-1, self.cls_out_channels) for item in cls_scores
]
bbox_preds = levels_to_images(bbox_preds)
bbox_preds = [item.reshape(-1, 4) for item in bbox_preds]
iou_preds = levels_to_images(iou_preds)
iou_preds = [item.reshape(-1, 1) for item in iou_preds]
# convert all tensor list to a flatten tensor
cls_scores = torch.cat(cls_scores, 0).view(-1, cls_scores[0].size(-1))
bbox_preds = torch.cat(bbox_preds, 0).view(-1, bbox_preds[0].size(-1))
iou_preds = torch.cat(iou_preds, 0).view(-1, iou_preds[0].size(-1))
losses_cls = self.loss_cls(
cls_scores,
labels,
labels_weight,
avg_factor=max(num_pos, len(img_metas))) # avoid num_pos=0
if num_pos:
pos_bbox_pred = self.bbox_coder.decode(
pos_anchors, bbox_preds[pos_inds_flatten])
pos_bbox_target = bboxes_target[pos_inds_flatten]
iou_target = bbox_overlaps(
pos_bbox_pred.detach(), pos_bbox_target, is_aligned=True)
losses_iou = self.loss_centerness(
iou_preds[pos_inds_flatten],
iou_target.unsqueeze(-1),
avg_factor=num_pos)
losses_bbox = self.loss_bbox(
pos_bbox_pred, pos_bbox_target, avg_factor=num_pos)
else:
losses_iou = iou_preds.sum() * 0
losses_bbox = bbox_preds.sum() * 0
return dict(
loss_cls=losses_cls, loss_bbox=losses_bbox, loss_iou=losses_iou)