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import numpy as np
import torch
from mmdet.core import bbox2roi
from mmdet.models.losses import SmoothL1Loss
from ..builder import HEADS
from .standard_roi_head import StandardRoIHead
EPS = 1e-15
@HEADS.register_module()
class DynamicRoIHead(StandardRoIHead):
"""RoI head for `Dynamic R-CNN <https://arxiv.org/abs/2004.06002>`_."""
def __init__(self, **kwargs):
super(DynamicRoIHead, self).__init__(**kwargs)
assert isinstance(self.bbox_head.loss_bbox, SmoothL1Loss)
# the IoU history of the past `update_iter_interval` iterations
self.iou_history = []
# the beta history of the past `update_iter_interval` iterations
self.beta_history = []
def forward_train(self,
x,
img_metas,
proposal_list,
gt_bboxes,
gt_labels,
gt_bboxes_ignore=None,
gt_masks=None):
"""Forward function for training.
Args:
x (list[Tensor]): list of multi-level img features.
img_metas (list[dict]): list of image info dict where each dict
has: 'img_shape', 'scale_factor', 'flip', and may also contain
'filename', 'ori_shape', 'pad_shape', and 'img_norm_cfg'.
For details on the values of these keys see
`mmdet/datasets/pipelines/formatting.py:Collect`.
proposals (list[Tensors]): list of region proposals.
gt_bboxes (list[Tensor]): each item are the truth boxes for each
image in [tl_x, tl_y, br_x, br_y] format.
gt_labels (list[Tensor]): class indices corresponding to each box
gt_bboxes_ignore (None | list[Tensor]): specify which bounding
boxes can be ignored when computing the loss.
gt_masks (None | Tensor) : true segmentation masks for each box
used if the architecture supports a segmentation task.
Returns:
dict[str, Tensor]: a dictionary of loss components
"""
# assign gts and sample proposals
if self.with_bbox or self.with_mask:
num_imgs = len(img_metas)
if gt_bboxes_ignore is None:
gt_bboxes_ignore = [None for _ in range(num_imgs)]
sampling_results = []
cur_iou = []
for i in range(num_imgs):
assign_result = self.bbox_assigner.assign(
proposal_list[i], gt_bboxes[i], gt_bboxes_ignore[i],
gt_labels[i])
sampling_result = self.bbox_sampler.sample(
assign_result,
proposal_list[i],
gt_bboxes[i],
gt_labels[i],
feats=[lvl_feat[i][None] for lvl_feat in x])
# record the `iou_topk`-th largest IoU in an image
iou_topk = min(self.train_cfg.dynamic_rcnn.iou_topk,
len(assign_result.max_overlaps))
ious, _ = torch.topk(assign_result.max_overlaps, iou_topk)
cur_iou.append(ious[-1].item())
sampling_results.append(sampling_result)
# average the current IoUs over images
cur_iou = np.mean(cur_iou)
self.iou_history.append(cur_iou)
losses = dict()
# bbox head forward and loss
if self.with_bbox:
bbox_results = self._bbox_forward_train(x, sampling_results,
gt_bboxes, gt_labels,
img_metas)
losses.update(bbox_results['loss_bbox'])
# mask head forward and loss
if self.with_mask:
mask_results = self._mask_forward_train(x, sampling_results,
bbox_results['bbox_feats'],
gt_masks, img_metas)
losses.update(mask_results['loss_mask'])
# update IoU threshold and SmoothL1 beta
update_iter_interval = self.train_cfg.dynamic_rcnn.update_iter_interval
if len(self.iou_history) % update_iter_interval == 0:
new_iou_thr, new_beta = self.update_hyperparameters()
return losses
def _bbox_forward_train(self, x, sampling_results, gt_bboxes, gt_labels,
img_metas):
num_imgs = len(img_metas)
rois = bbox2roi([res.bboxes for res in sampling_results])
bbox_results = self._bbox_forward(x, rois)
bbox_targets = self.bbox_head.get_targets(sampling_results, gt_bboxes,
gt_labels, self.train_cfg)
# record the `beta_topk`-th smallest target
# `bbox_targets[2]` and `bbox_targets[3]` stand for bbox_targets
# and bbox_weights, respectively
pos_inds = bbox_targets[3][:, 0].nonzero().squeeze(1)
num_pos = len(pos_inds)
cur_target = bbox_targets[2][pos_inds, :2].abs().mean(dim=1)
beta_topk = min(self.train_cfg.dynamic_rcnn.beta_topk * num_imgs,
num_pos)
cur_target = torch.kthvalue(cur_target, beta_topk)[0].item()
self.beta_history.append(cur_target)
loss_bbox = self.bbox_head.loss(bbox_results['cls_score'],
bbox_results['bbox_pred'], rois,
*bbox_targets)
bbox_results.update(loss_bbox=loss_bbox)
return bbox_results
def update_hyperparameters(self):
"""Update hyperparameters like IoU thresholds for assigner and beta for
SmoothL1 loss based on the training statistics.
Returns:
tuple[float]: the updated ``iou_thr`` and ``beta``.
"""
new_iou_thr = max(self.train_cfg.dynamic_rcnn.initial_iou,
np.mean(self.iou_history))
self.iou_history = []
self.bbox_assigner.pos_iou_thr = new_iou_thr
self.bbox_assigner.neg_iou_thr = new_iou_thr
self.bbox_assigner.min_pos_iou = new_iou_thr
if (np.median(self.beta_history) < EPS):
# avoid 0 or too small value for new_beta
new_beta = self.bbox_head.loss_bbox.beta
else:
new_beta = min(self.train_cfg.dynamic_rcnn.initial_beta,
np.median(self.beta_history))
self.beta_history = []
self.bbox_head.loss_bbox.beta = new_beta
return new_iou_thr, new_beta
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