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# Copyright (c) OpenMMLab. All rights reserved.
from typing import List, Optional, Tuple
import torch
from mmengine.structures import InstanceData
from torch import Tensor
from mmdet.registry import TASK_UTILS
from ..prior_generators import anchor_inside_flags
from .assign_result import AssignResult
from .base_assigner import BaseAssigner
def calc_region(
bbox: Tensor,
ratio: float,
stride: int,
featmap_size: Optional[Tuple[int, int]] = None) -> Tuple[Tensor]:
"""Calculate region of the box defined by the ratio, the ratio is from the
center of the box to every edge."""
# project bbox on the feature
f_bbox = bbox / stride
x1 = torch.round((1 - ratio) * f_bbox[0] + ratio * f_bbox[2])
y1 = torch.round((1 - ratio) * f_bbox[1] + ratio * f_bbox[3])
x2 = torch.round(ratio * f_bbox[0] + (1 - ratio) * f_bbox[2])
y2 = torch.round(ratio * f_bbox[1] + (1 - ratio) * f_bbox[3])
if featmap_size is not None:
x1 = x1.clamp(min=0, max=featmap_size[1])
y1 = y1.clamp(min=0, max=featmap_size[0])
x2 = x2.clamp(min=0, max=featmap_size[1])
y2 = y2.clamp(min=0, max=featmap_size[0])
return (x1, y1, x2, y2)
def anchor_ctr_inside_region_flags(anchors: Tensor, stride: int,
region: Tuple[Tensor]) -> Tensor:
"""Get the flag indicate whether anchor centers are inside regions."""
x1, y1, x2, y2 = region
f_anchors = anchors / stride
x = (f_anchors[:, 0] + f_anchors[:, 2]) * 0.5
y = (f_anchors[:, 1] + f_anchors[:, 3]) * 0.5
flags = (x >= x1) & (x <= x2) & (y >= y1) & (y <= y2)
return flags
@TASK_UTILS.register_module()
class RegionAssigner(BaseAssigner):
"""Assign a corresponding gt bbox or background to each bbox.
Each proposals will be assigned with `-1`, `0`, or a positive integer
indicating the ground truth index.
- -1: don't care
- 0: negative sample, no assigned gt
- positive integer: positive sample, index (1-based) of assigned gt
Args:
center_ratio (float): ratio of the region in the center of the bbox to
define positive sample.
ignore_ratio (float): ratio of the region to define ignore samples.
"""
def __init__(self,
center_ratio: float = 0.2,
ignore_ratio: float = 0.5) -> None:
self.center_ratio = center_ratio
self.ignore_ratio = ignore_ratio
def assign(self,
pred_instances: InstanceData,
gt_instances: InstanceData,
img_meta: dict,
featmap_sizes: List[Tuple[int, int]],
num_level_anchors: List[int],
anchor_scale: int,
anchor_strides: List[int],
gt_instances_ignore: Optional[InstanceData] = None,
allowed_border: int = 0) -> AssignResult:
"""Assign gt to anchors.
This method assign a gt bbox to every bbox (proposal/anchor), each bbox
will be assigned with -1, 0, or a positive number. -1 means don't care,
0 means negative sample, positive number is the index (1-based) of
assigned gt.
The assignment is done in following steps, and the order matters.
1. Assign every anchor to 0 (negative)
2. (For each gt_bboxes) Compute ignore flags based on ignore_region
then assign -1 to anchors w.r.t. ignore flags
3. (For each gt_bboxes) Compute pos flags based on center_region then
assign gt_bboxes to anchors w.r.t. pos flags
4. (For each gt_bboxes) Compute ignore flags based on adjacent anchor
level then assign -1 to anchors w.r.t. ignore flags
5. Assign anchor outside of image to -1
Args:
pred_instances (:obj:`InstanceData`): Instances of model
predictions. It includes ``priors``, and the priors can
be anchors or points, or the bboxes predicted by the
previous stage, has shape (n, 4). The bboxes predicted by
the current model or stage will be named ``bboxes``,
``labels``, and ``scores``, the same as the ``InstanceData``
in other places.
gt_instances (:obj:`InstanceData`): Ground truth of instance
annotations. It usually includes ``bboxes``, with shape (k, 4),
and ``labels``, with shape (k, ).
img_meta (dict): Meta info of image.
featmap_sizes (list[tuple[int, int]]): Feature map size each level.
num_level_anchors (list[int]): The number of anchors in each level.
anchor_scale (int): Scale of the anchor.
anchor_strides (list[int]): Stride of the anchor.
gt_instances_ignore (:obj:`InstanceData`, optional): Instances
to be ignored during training. It includes ``bboxes``
attribute data that is ignored during training and testing.
Defaults to None.
allowed_border (int, optional): The border to allow the valid
anchor. Defaults to 0.
Returns:
:obj:`AssignResult`: The assign result.
"""
if gt_instances_ignore is not None:
raise NotImplementedError
num_gts = len(gt_instances)
num_bboxes = len(pred_instances)
gt_bboxes = gt_instances.bboxes
gt_labels = gt_instances.labels
flat_anchors = pred_instances.priors
flat_valid_flags = pred_instances.valid_flags
mlvl_anchors = torch.split(flat_anchors, num_level_anchors)
if num_gts == 0 or num_bboxes == 0:
# No ground truth or boxes, return empty assignment
max_overlaps = gt_bboxes.new_zeros((num_bboxes, ))
assigned_gt_inds = gt_bboxes.new_zeros((num_bboxes, ),
dtype=torch.long)
assigned_labels = gt_bboxes.new_full((num_bboxes, ),
-1,
dtype=torch.long)
return AssignResult(
num_gts=num_gts,
gt_inds=assigned_gt_inds,
max_overlaps=max_overlaps,
labels=assigned_labels)
num_lvls = len(mlvl_anchors)
r1 = (1 - self.center_ratio) / 2
r2 = (1 - self.ignore_ratio) / 2
scale = torch.sqrt((gt_bboxes[:, 2] - gt_bboxes[:, 0]) *
(gt_bboxes[:, 3] - gt_bboxes[:, 1]))
min_anchor_size = scale.new_full(
(1, ), float(anchor_scale * anchor_strides[0]))
target_lvls = torch.floor(
torch.log2(scale) - torch.log2(min_anchor_size) + 0.5)
target_lvls = target_lvls.clamp(min=0, max=num_lvls - 1).long()
# 1. assign 0 (negative) by default
mlvl_assigned_gt_inds = []
mlvl_ignore_flags = []
for lvl in range(num_lvls):
assigned_gt_inds = gt_bboxes.new_full((num_level_anchors[lvl], ),
0,
dtype=torch.long)
ignore_flags = torch.zeros_like(assigned_gt_inds)
mlvl_assigned_gt_inds.append(assigned_gt_inds)
mlvl_ignore_flags.append(ignore_flags)
for gt_id in range(num_gts):
lvl = target_lvls[gt_id].item()
featmap_size = featmap_sizes[lvl]
stride = anchor_strides[lvl]
anchors = mlvl_anchors[lvl]
gt_bbox = gt_bboxes[gt_id, :4]
# Compute regions
ignore_region = calc_region(gt_bbox, r2, stride, featmap_size)
ctr_region = calc_region(gt_bbox, r1, stride, featmap_size)
# 2. Assign -1 to ignore flags
ignore_flags = anchor_ctr_inside_region_flags(
anchors, stride, ignore_region)
mlvl_assigned_gt_inds[lvl][ignore_flags] = -1
# 3. Assign gt_bboxes to pos flags
pos_flags = anchor_ctr_inside_region_flags(anchors, stride,
ctr_region)
mlvl_assigned_gt_inds[lvl][pos_flags] = gt_id + 1
# 4. Assign -1 to ignore adjacent lvl
if lvl > 0:
d_lvl = lvl - 1
d_anchors = mlvl_anchors[d_lvl]
d_featmap_size = featmap_sizes[d_lvl]
d_stride = anchor_strides[d_lvl]
d_ignore_region = calc_region(gt_bbox, r2, d_stride,
d_featmap_size)
ignore_flags = anchor_ctr_inside_region_flags(
d_anchors, d_stride, d_ignore_region)
mlvl_ignore_flags[d_lvl][ignore_flags] = 1
if lvl < num_lvls - 1:
u_lvl = lvl + 1
u_anchors = mlvl_anchors[u_lvl]
u_featmap_size = featmap_sizes[u_lvl]
u_stride = anchor_strides[u_lvl]
u_ignore_region = calc_region(gt_bbox, r2, u_stride,
u_featmap_size)
ignore_flags = anchor_ctr_inside_region_flags(
u_anchors, u_stride, u_ignore_region)
mlvl_ignore_flags[u_lvl][ignore_flags] = 1
# 4. (cont.) Assign -1 to ignore adjacent lvl
for lvl in range(num_lvls):
ignore_flags = mlvl_ignore_flags[lvl]
mlvl_assigned_gt_inds[lvl][ignore_flags == 1] = -1
# 5. Assign -1 to anchor outside of image
flat_assigned_gt_inds = torch.cat(mlvl_assigned_gt_inds)
assert (flat_assigned_gt_inds.shape[0] == flat_anchors.shape[0] ==
flat_valid_flags.shape[0])
inside_flags = anchor_inside_flags(flat_anchors, flat_valid_flags,
img_meta['img_shape'],
allowed_border)
outside_flags = ~inside_flags
flat_assigned_gt_inds[outside_flags] = -1
assigned_labels = torch.zeros_like(flat_assigned_gt_inds)
pos_flags = flat_assigned_gt_inds > 0
assigned_labels[pos_flags] = gt_labels[flat_assigned_gt_inds[pos_flags]
- 1]
return AssignResult(
num_gts=num_gts,
gt_inds=flat_assigned_gt_inds,
max_overlaps=None,
labels=assigned_labels)
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